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Measurement of the isotope ratio of acetic acid in vinegar by HS-SPME-GC-TC/C-IRMS
Abstract
Acetic acid is the main ingredient of vinegar, and the worth of vinegar often depends on the fermentation of raw materials. In this study, we have developed a simple and rapid method for discriminating the fermentation of the raw materials of vinegar by measuring the hydrogen and carbon isotope ratio of acetic acid using head space solid-phase microextraction (HS-SPME) combined with gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS). The measurement of acetic acid in vinegar by this method was possible with repeatabilities (1sigma) of +/-5.0 per thousand for hydrogen and +/-0.4 per thousand for carbon, which are sufficient to discriminate the origin of acetic acid. The fermentation of raw materials of several vinegars was evaluated by this method.
... [64] Hydrogen and carbon isotope ratios were determined as effective parameters to discriminate the botanical origins of the acetic acid. The difference between C3 and C4 plants was [62] Determination of carbon isotope distribution in vinegar acetic acid Commercial Japanese vinegars Targeted Improved gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) Low concentrations of acetic acid in complex media such as food products were measurable by the SPME technique [63] Discrimination of raw materials used in fermentation Rice vinegar, tomato vinegar, apple vinegar, pineapple vinegar, lychee vinegar, grain vinegar, wheat vinegar Targeted Head space solid-phase microextraction (HS-SPME) combined with gas chromatographyhigh temperature conversion or combustionisotope ratio mass spectrometry (GC-TC /C-IRMS) ...
... Following this study, same sample composition was also used to determine δ 13 C values of methyl and carboxyl carbons of acetic acid with gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) since each carbon isotope ratios of methyl and carboxyl groups in acetic molecules could be indicators of the origin. [63] Therefore, findings of this study were expected to assist in the determination of indigenously and exogenously produced sources of acetic acid. Stable isotope methods using hydrogen, carbon and oxygen isotope analyses by isotope ratio mass and H-2-NMR spectrometry were also proposed to check the authenticity of balsamic vinegar. ...
... Stable isotope methods using hydrogen, carbon and oxygen isotope analyses by isotope ratio mass and H-2-NMR spectrometry were also proposed to check the authenticity of balsamic vinegar. [63,68] Scatter plot of δ 13 C versus δ 2 H values of acetic acid (calcium acetate) from balsamic vinegar demonstrated successful visual discrimination of pure wine acetic acid, C4 plant acetic acid added samples, and C3 plant acetic acid added samples. δ 18 O analysis of water with isotope ratio mass spectrometer was used to determine the production of wine vinegar through fermentation of dried gapes and dilution with tap water which is against the EU regulation (EU Regulation 555/2008). ...
There has been a growing interest in vinegar, especially after the increasing reports about its beneficial health effects. Bioactive compounds of vinegar are associated with its antimicrobial, antioxidant, antidiabetic, antitumor, and anti-obesity types of activities. Quality of vinegar is related with the authenticity of the product besides the amounts of bioactive compounds in its composition. Addition of cheaper substitutes to higher quality vinegars and false labeling are some common authentication problems for this product. There are various examples of the use of targeted and untargeted methods in authentication studies for vinegars. Specific constituents and properties of vinegars such as molecular isotope ratios and individual volatile compounds were used to detect adulteration with targeted methods. On the other hand, untargeted methods, mostly in the form of the application of spectroscopic techniques, such as infrared and fluorescence spectroscopy in combination with chemometrics, provide an overall measurement. This review mainly focuses on adulteration types and elaborates on different targeted and non-targeted methods used to authenticate vinegars.
... Fractionation also describes variations in the stable isotope ratios of carbon brought about by non-natural causes (laboratoryinduced fractionation) [17]. Irreproducible isotopic fractionation can vary depending on fibre placement (immersion or headspace), fibre type, temperature, time, and the physicochemical properties of the analytes [18]. ...
... carbon) itself may not provide the discriminatory power required to determine authenticity, which means that the characterisation of an additional element, such as hydrogen could be beneficial. Previously, however, only a few studies have included hydrogen isotope measurements, and only Perini et al. (2019) [16] and Hattori et al. (2010) [18] combine SPME with gas-chromatography-high temperature conversion-specific isotope ratio mass spectrometry (GC-HTC-IRMS), to study vanillin and acetic acid, respectively [8]. ...
... carbon) itself may not provide the discriminatory power required to determine authenticity, which means that the characterisation of an additional element, such as hydrogen could be beneficial. Previously, however, only a few studies have included hydrogen isotope measurements, and only Perini et al. (2019) [16] and Hattori et al. (2010) [18] combine SPME with gas-chromatography-high temperature conversion-specific isotope ratio mass spectrometry (GC-HTC-IRMS), to study vanillin and acetic acid, respectively [8]. ...
Natural flavouring materials are in high demand, and a premium price is paid for all-natural flavourings, making them vulnerable to fraud. At present, compound-specific isotope analysis (CSIA) is perhaps the most sophisticated tool for determining flavour authenticity. Despite promising results, the method is not widely used, and the results are limited to the most common volatile organic compounds (VOCs). This paper describes a robust protocol for on-line measurements of δ¹³C and δ²H using HS-SPME coupled with GC-C-IRMS and GC--HTC-IRMS for common fruit. To achieve reproducible and accurate results, a combination of a peak size/linearity correction with drift correction were used. Finally, the results were normalised by multiple point linear regression using the known and measured values for reference materials. Special care was taken to avoid irreproducible isotopic fractionation and the effects of equilibration, adsorption, desorption times and temperatures on δ¹³C or δ²H values were examined. Method validation was performed, and the average combined measurement uncertainty (MU) was 0.42‰. All the δ¹³CVPDB values were below ±3*MU, regardless of analytical conditions. In contrast, for δ²HVSMOW-SLAP values, only low temperature (30 °C) with equilibration time (15 min) and shorter adsorption time (between 10 and 20 min) can produce an isotopic difference of <10‰. Therefore, method optimisation can minimise MU, and data normalisation and method validation are essential for obtaining meaningful data for use in flavour authenticity studies.
... Furthermore, it is prone to introduce isotope fractionation. More recently, limited degradation coupled with on-line pyrolysis and GC separation of fragments (Py-GC-irm-MS) has been developed [8], but at present this is limited to small molecules such as acetic acid, lactic acid or ethanol [9][10][11][12][13]. ...
... It has been shown by Py-GC-irm-MS that the d 13 C values of the methyl group (d 13 C CH 3 ) and of the carboxylic function (d 13 C COOH ) of acetic acid can vary considerably according to the origin (botanical, metabolic pathway, synthetic, physical transformation) even when the d 13 C g value remains nearly identical [11,12]. Taking into account the industrial and biological importance of this molecule, it is thus a prime target for iq-13 C NMR. Therefore, it is a useful objective to establish whether the same values of trueness, intra-and interinstrument variability defined for ethanol can be applied for acetic acid. ...
... But as mentioned in Section 1, the intramolecular composition is not accessible for most molecules by irm-MS. The combination of a pyrolysis module to a GC-irm-MS (Py-GC-irm-MS) allows the determination of the position-specific d 13 C i in a number of small molecules, including ethanol [20,24] and acetic acid [11,12]. When this technique is applied to the same samples of acetic acid as studied by iq-13 C NMR, there is a good agreement between the values of d 13 C CH 3 and d 13 C COOH from MS and the NMR spectrometer 400B ( Table 2). ...
A stable isotopic composition in materials has provided useful information concerning their origins and histories. For a carbon isotopic measurement of a single organic molecule, the total organic carbon contained in the molecule should be converted quantitatively to carbon dioxide. Therefore, the carbon isotopic composition represents an average value for the molecules. In principle, information concerning the origins and histories of organic molecules exists at the specific position of the molecule. To retrieve diverse, complex, and specific information of their origins and histories from organic molecules, a measurement of the position-specific carbon isotopic composition is required. So far, a difficult measurement have prevented any development for the position-specific isotopic measurement. Here, we describe recent advances in analytical instrumentation concerning a position-specific carbon isotopic measurement for organic molecules using gas chromatography-combustion-isotope ratio mass spectrometry combined with an on-line pyrolysis technique.
... Furthermore, it is prone to introduce isotope fractionation. More recently, limited degradation coupled with on-line pyrolysis and GC separation of fragments (Py-GC-irm-MS) has been developed [8], but at present this is limited to small molecules such as acetic acid, lactic acid or ethanol [9][10][11][12][13]. ...
... It has been shown by Py-GC-irm-MS that the d 13 C values of the methyl group (d 13 C CH 3 ) and of the carboxylic function (d 13 C COOH ) of acetic acid can vary considerably according to the origin (botanical, metabolic pathway, synthetic, physical transformation) even when the d 13 C g value remains nearly identical [11,12]. Taking into account the industrial and biological importance of this molecule, it is thus a prime target for iq-13 C NMR. Therefore, it is a useful objective to establish whether the same values of trueness, intra-and interinstrument variability defined for ethanol can be applied for acetic acid. ...
... But as mentioned in Section 1, the intramolecular composition is not accessible for most molecules by irm-MS. The combination of a pyrolysis module to a GC-irm-MS (Py-GC-irm-MS) allows the determination of the position-specific d 13 C i in a number of small molecules, including ethanol [20,24] and acetic acid [11,12]. When this technique is applied to the same samples of acetic acid as studied by iq-13 C NMR, there is a good agreement between the values of d 13 C CH 3 and d 13 C COOH from MS and the NMR spectrometer 400B ( Table 2). ...
... The methyl-group hydrogens on MPn are ultimately derived from the water in which MPn is biosynthesized, offset by an unknown isotope effect. The hydrogen isotope fractionation between methyl-group hydrogens and water in more thoroughly studied processes, such as acetogenesis, show offsets from bulk water dD of hundreds of permil (Hattori et al., 2010). Here we utilized synthetic MPn with an average dD value distinct from all medium waters utilized (see Results). ...
... Indeed, the other canonical microbial pathways of methane formation, methylotrophic or acetotrophic, are clear analogs to the C-P lyase pathway, in that different D/H pools are accessed in the form of water and preexisting methyl groups, suggesting that exogenous combinatorial effects are at play. This is especially true given the likelihood for large D/H fractionations between water and C-H bearing organic sources of H in nature (Hattori et al., 2010), without which reservoir (exogenous) combinatorial effects are unlikely. More work is required to understand whether or not differences in D 12 CH 2 D 2 val-ues among different methanogenesis pathways (Giunta et al., 2019;Young et al., 2017) could in part reflect the different magnitudes of endogenous and exogenous combinatorial effects. ...
Methane generated by microorganisms is most often depleted in the doubly substituted isotopologue ¹²CH2D2 relative to the stochastic reference distribution. To constrain the controls on depleted Δ¹²CH2D2 values, we experimentally isolated the root cause with microorganisms that produce methane from methylphosphonate via the C-P lyase pathway. This mechanism of methane production preserves the three hydrogens from methylphosphonate and adds one hydrogen from water. When maintaining the same methylphosphonate source, but varying the D/H composition of growth medium water, we observed significant shifts in methane Δ¹²CH2D2 values, but little to no change in values. We reproduced these observations with a model that considers only the combinatorial isotope effect. The variation in Δ¹²CH2D2 values of product methane resulted from the differences in D/H between reactants water and methylphosphonate. This work validates the hypothesis that combinatorial effects can strongly influence methane Δ¹²CH2D2 values, and must be considered for low temperature, abiotic or biotic systems where methane hydrogen is derived from multiple reservoirs.
... Hattori et al. [34] developed a simple and rapid method able to discriminate among the fermentation of the raw materials employed in vinegar by measuring the hydrogen and carbon isotope ratio of acetic acid using head space solid-phase microextraction (HS-SPME) combined with gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS). A GC-conversion interface was used for hydrogen measurements, and a GC-combustion interface was used for carbon measurements. ...
... δD and δ13 C values of acetic acid in vinegars of different raw materials. Reprinted with permission of reference[34]. Copyright (2010) American Chemical Society. ...
Food adulteration practices are potentially harmful to human health and so food safety and authenticity constitute an important issue in food chemistry. The chemical composition of foodstuffs is an excellent indicator of quality, origin, authenticity and/or adulteration. In general, food adulteration is carried out to increase volume, to mask the presence of inferior quality components, and to replace the authentic substances for the seller’s economic gain. For instance, a common fraud is the employment of a cheaper similar ingredient, which the consumer has difficulty recognizing and which is difficult to detect by current analytical methodologies. For example, fruit-processed products are common adulterated by addition of water, sugars, fruits of inferior commercial values, secondary extracts of fruits and colors, etc. In other cases, the fraud is related to an incorrect labelling of the food product, for example, when refined or lower quality olive oils are labeled as extra-virgin olive oils. Thus, the development of analytical methodologies to achieve food authentication and to identify food frauds is required.
Gas chromatography coupled to mass spectrometry (GC-MS) is nowadays one of the most employed techniques to address food authenticity issues especially by the non-targeted fingerprinting of the food volatolome (volatile metabolites present in the foodstuffs). Targeted strategies by focusing either in the determination of specific food biomarkers or by the profiling of selected families of chemical compounds such as fatty acids are also employed within GC methodologies for authentication purposes. Compound-specific isotope analysis by isotope ratio mass spectrometry (IRMS) following the on-line combustion of compounds separated by GC has also become a method of choice in the authenticity control of foodstuffs based on the measurement of the isotope distribution at natural abundance level. In addition, multidimensional gas chromatography coupled with mass spectrometry has become also a powerful tool in food analysis, being also employed in food authentication problems. In this chapter, the role of GC-MS techniques for food authentication and the identification and prevention of frauds will be addressed. Coverage of all kind of applications is beyond the scope of the present contribution, so the present chapter will focus on the most relevant applications published in the last years.
... The ratios of 2 H/ 1 H range from 90 to 110 ppm for authentic vinegar (depending on botanical origin) and from 120 to 140 ppm for synthetic acetic acid; the values of δ 13 C range from −30 to −10 ‰ for authentic vinegar and from −40 to −30 ‰ for synthetic acetic acid; it is obvious that it is necessary to determine both isotope ratios to determine sample origin reliably [6,7,11]. In agreement with the literature, the isotope ratios for the authentic vinegars from the Czech marked ranged from 90.30 to 109.60 ppm ( 2 H/ 1 H) and from −12.30 to −28.80 ‰ ( 13 C/ 12 C); for the synthetic acetic acids, they ranged from 114.20 to 124.90 ppm ( 2 H/ 1 H) and from −32.50 to −42.40 ‰ ( 13 C/ 12 C) [12]. ...
... The final suggested sample preparation procedure, given in the Materials and methods section, was used to analyse both the real and the model pickles. In agreement with the literature [6,7,11], the measured ratios of 2 H/ 1 H and 13 C/ 12 C (δ 13 C) for the samples which had been proved to be authentic pickled cucumbers ranged from 89.4 to 107.0 ppm and from −28.7 to −15.6 ‰, respectively. For the model pickles, the mixtures of vinegar and synthetic acetic acid (including both models in 8:2 and 7.5:2.5 ratios), they ranged from 101.1 to 111.5 ppm and −28.2 to −19.1 ‰, respectively. ...
Possible adulteration of canned products containing spirit vinegar pickle by adding synthetic acetic acid is a significant problem of the food industry. Isotope analyses, which determine botanical origin of acetic acid and also can detect synthetic acid, were applied to detect undeclared addition of synthetic acetic acid to canned products. The aim of the study was to improve the extraction technique for the SNIF-NMR (2H/1H; site-specific natural isotopic fractionation-nuclear magnetic resonance) and IRMS (13C/12C; isotope ratio mass spectrometry) isotope methods and for an atypical matrix and to determine isotope ratios in canned vegetables pickle to prove their adulteration or authenticity. The following set of canned products was analysed: pickled cucumbers (n = 16) and one vinegar pickle purchased in the Czech market and six model (cucumber) pickles. The determined ratios of 2H/1H and 13C/12C for the pickled cucumbers proved to be authentic ranged from 89.4 to 107.0 ppm and from −28.7 to −15.6 ‰, respectively; for the synthetic acetic acids diluted with water they ranged from 114.2 to 129.0 ppm and from −44.9 to −33.4 ‰, respectively. Isotope analyses were confirmed as a reliable tool for assessing authenticity of canned products. The method enables detection of synthetic acetic acid addition into vinegars and canned vegetables containing vinegar pickle up from 20 % (of total acidity).
... Polyethylene glycol stationary phases are commonly used in GC/IRMS analyses for their selectivity in separating polar compounds such as ethanol and acetic acid. [5][6][7][8]11,26] In our study, water was used as the GC/IRMS injection solvent. For aqueous injections, a relatively high maximum GC column temperature should be employed for a relatively long time (typically higher than 200°C for at least 5 min) to remove traces of water retained in the GC/IRMS system in every run. ...
... He also found identical chromatographic performance after 2000 injections of a water sample on a polyethylene glycol column. [28] Following the publication of a LC/IRMS method for the isotope ratio analysis of methanol, ethanol and acetic acid in aqueous solutions, [12] several methods for the GC/IRMS analysis of aqueous ethanol [6] and acetic acid [7,8] have been reported. The GC-Isolink interface has a high resolution capacity and high sensitivity, is easy to operate and is readily available. ...
Rationale:
Methanol, ethanol, and acetic acid are not easily extracted from aqueous samples and are susceptible to isotope fractionation in gas chromatography/isotope ratio mass spectrometry (GC/IRMS) analysis. Developing a direct dilution GC/IRMS method for aqueous samples, by adjusting the sample concentrations in common solvents to be similar to each other and using a fixed GC split ratio, is very convenient and important because any linearity effects caused by amount-dependent isotope fractionation can be avoided.
Methods:
The suitability of acetonitrile and acetone solvents for the GC/IRMS analysis of pure methanol, ethanol and acetic acid, and commercial liquor and vinegar samples was evaluated using n-hexane and water as control solvents. All the solvents including water were separated from the analyte on a HP-INNOWAX column and were diverted away from the combustion interface. The influence of liquor matrix on the ethanol GC/IRMS analyses was evaluated by adding pure ethanol to liquor samples.
Results:
Acetonitrile and acetone gave similar δ(13) C values for pure ethanol and pure acetic acid to those obtained in water and n-hexane, and also gave similar δ(13) C values of ethanol in liquor and acetic acid in white vinegar to that obtained in water. For methanol analysis, acetonitrile and refined acetone gave similar δ(13) C values to that obtained in water, but n-hexane was not a suitable solvent. In addition, isotopic fractionation caused by solvent and solute interactions was observed.
Conclusions:
We recommend using acetonitrile for the GC/IRMS analysis of aqueous alcoholic samples, and acetone for the analysis of aqueous acetic acid samples. This direct dilution method can provide high accurate and precise GC/IRMS analysis of the relative changes in δ(13) C values of methanol, ethanol, and acetic acid.
... Geographical indications (GIs) are lace-based names that convey the geographical origin, as well as the cultural and historical identity, of agricultural products. The vinegar originating from C3 or C4 plants, and also nd whether or not industrial acetic acid is added to the vinegar product (Hattori et al. 2010). By using the total carbon isotope ratio, the carbon isotope ratio of acetic acids, and organic acids(Gregrova et al. 2012) detected by IRMS, authenticity identi cation of vinegar can be achieved preliminary. ...
Shanxi extra-aged vinegar (SX) and Zhenjiang vinegar (ZJ) are two kinds of well-known vinegar in China, always counterfeited in the market due to their geographical indication labels. The carbon isotope ratio data ( δ ¹³ C) measured by elementary analyzer isotope ratio mass spectrometer (EA-IRMS), were used to distinguish two geographical indications of vinegar (SX and ZJ) from other vinegar samples with different producing regions. The δ ¹³ C value data of vinegar, the protein extracted from vinegar, and the sugar extracted from vinegar were measured separately. It was found that using each of the three kinds of δ ¹³ C value as a single parameter to vinegar distinguishment is not practicable. Hence, the linear discriminant analysis (LDA) discriminant analysis model was established for vinegar distinguishment by using all three kinds of δ ¹³ C data as multi-indicators. The results indicated 24 SX and 35 ZJ vinegar samples could be obviously discriminated from the other 26 vinegar samples in this distinguishment model. This data suggested that EA-IRMS coupled with LDA could be used as a further tool for vinegar traceability and geographical indications protection.
... SPME is a solvent-free, inexpensive, and sensitive method, as reported by Pawliszyn [29] and Pawliszyn [30]. Some studies of carbon stable isotope analysis using SPME have been conducted previously [e.g., [31][32][33][34][35][36][37][38], but the target media in all of these studies were aqueous rather than air samples. In addition, some reports have indicated that the achievable fractionation in δ 13 C using SPME/GC/C/IRMS is very small [33]. ...
The isotopic analysis of atmospheric volatile organic compounds (VOCs), and in particular their carbon isotope ratio (δ¹³C), has the potential to be an effective tool for clearly identifying sources of these pollutants. However, to date, there have been very few such analyses. In the work described herein, we have attempted to analyze the δ¹³C values of VOCs using solid-phase micro-extraction (SPME) coupled with chromatography, combustion, and isotope ratio mass spectrometry (SPME-GC/C/IRMS). The collection and equilibration of VOCs on an SPME fiber required approximately 700−800 min. Although this sample acquisition time is relatively long, extraction and analysis could be achieved reasonably rapidly. The δ¹³C values of benzene, trichloroethylene, toluene, tetrachloroethylene, ethylbenzene, m,p-xylenes, styrene, and o-xylene in a 200 ppb standard gas determined by SPME-GC/C/IRMS ranged from − 29.7‰ to − 22.9‰. The standard deviations ranged from ± 0.4 to ± 1.6‰, and were thus very reasonable compared to those in other studies. In addition, we tested air samples with concentrations ranging from 5 to 500 ppb. In general, because the reasonable precision of GC/C/IRMS is < 0.2‰, the required area of SPME-GC/C/IRMS ranged from 12 Vs (o-xylene) to 50 Vs (m,p-xylenes). The δ¹³C values of benzene for vehicle exhaust and in the vicinity of a gas station were − 25.3 ± 1.0‰ and − 26.2 ± 0.7‰, respectively. Compared with other references, the data in this study were reasonable. The detected differences between gasoline and vehicle emissions were similar to those in previous research. Our δ¹³C value of benzene for vehicle exhaust closely resembled values in the vicinity of a gas station. This narrow range may have been because vehicle exhaust samples in this research were collected in cold start mode rather than hot mode. Benzene in gasoline can be emitted through the tail pipe due to inactivity of the catalyst in cold mode.
... erefore, stable isotope detection technology combined with mineral element content analysis is the most effective method to trace the origin of agricultural products [5]. At present, this technology has been widely used in the origin traceability of wine [6], beer [7], spring water [8], tea [9], coffee [10], rice [11], lamb [12], beef [13], poultry meat [14], edible vinegar [15], wheat [16], and cocoa [17]. It has provided strong technical support for the protection of geographical indications of world-renowned agricultural products and processed products. ...
The primary aim of this paper was to identifying the geographical origin of tobacco leaves based on stable isotopic and mineral elemental fingerprint. We collected eighty-one tobacco leaf samples from Argentina, Brazil, Zimbabwe, the U.S., Zambia, and China. And nine mineral element contents and four strontium and lead isotope ratios of the tobacco leaves were determined by thermal ionization mass spectrometry (TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). After variance and stepwise discriminant analysis, the discriminant functions of the tobacco leaf’s geographical origin were established. The results indicate that: (1) the contents of six mineral elements including Cu, Zn, Cr, Ni, Cd, and Pb, together with four strontium and lead isotope ratios containing 87Sr/86Sr, 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb, were significantly different among six countries. (2) Different countries presented some characteristic mineral elemental and isotopic fingerprint. The even contents of mineral elements from Zambian tobacco leaf were much lower than the other countries, among which four elements consisting of Zn, Cr, As, and Cd were not detected. The three average lead isotope ratios including 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb from Zimbabwe tobacco leaves were far higher than the other countries, and the range of which was unoverlapped. (3) The effective identification of the geographical origin of tobacco leaf was accomplished by Fisher stepwise discriminant analysis and the characteristic tracing elements consisted of Cu, Zn, Cr, Ni, Cd, Pb, 87Sr/86Sr, 207Pb/204Pb, and 206Pb/204Pb. Based on the established discriminant functions, the original and cross-validation accuracy towards different geographical origins of tobacco leaves were 98.8% and 95.1%, respectively. The study shows that the strontium and lead isotopic with mineral elemental fingerprints is a potential effective method to identify the geographical origin of tobacco leaves from different countries.
... Then the analytical gases evolved from the sample are delivered to a mass spectrometer, and the stable isotopic ratios of the sample are determined. Some past studies have applied these techniques to vinegar for tracing the source of raw materials used in production [11,12]. ...
Rice vinegar plays an important role in daily life. However, some unscrupulous manufacturers may deliberately add synthetic acetic acid in vinegar products to reduce fermentation time and save production costs. To protect the rights and health of consumers, vinegar authenticity must be controlled. The rice vinegar protein was used as an intrinsic reference and its stable carbon isotope ratio (δ13Cprotein) was analyzed by elemental analyzer-isotope ratio mass spectrometry. The stable carbon isotope ratio difference between the acetic acid and the rice vinegar protein (Δδ13Cacetic acid-protein) was calculated to evaluate vinegar authenticity. Sixteen rice vinegar samples were analyzed and a stable carbon isotopic pattern of rice vinegar was established by the 95% confidence interval for Δδ13Cacetic acid-protein (0.27‰-2.10‰). An acetic acid adulteration curve of Δδ13Cacetic acid-protein was also assumed according to the data from rice vinegar samples, and its validity was confirmed by rice vinegar deliberately blended with acetic acid at different ratios (25, 50, and 75%). The Δδ13Cacetic acid-protein values of the adulterated vinegars decreased with increasing amounts blended acetic acid, but the δ13Cprotein values did not, showing that rice vinegar protein could be used as an intrinsic reference for identifying the adulterated rice vinegar. The rice vinegar adulterated with acetic acid at higher than approximately 10% could be detected.
... There are several studies regarding the detection of acetic acid and spirit vinegar added to vinegars with various techniques in the literature. δ 13 C values originating from methyl and carboxyl groups in acetic acid were determined with head space-solid phase micro extraction (HS-SPME) combined with gas chromatography pyrolysis gas chromatography combustion isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) technique and used successfully in detecting the addition of low levels of acetic acid to commercial Japanese vinegars (Hattori et al., 2010). In another study, determination of acetic acid added to balsamic vinegar was aimed and it was investigated to build a multi-step method including GC-IRMS measurement which was validated with 1H NMR spectroscopic technique (Werner and Roßmann, 2015). ...
Vinegar is one of the commonly adulterated food products, and variations in product and adulterant spectrum make the detection of adulteration a challenging task. This study aims to determine adulteration of grape vinegars with spirit vinegar and synthetic acetic acid using different spectroscopic methods. For this purpose, grape vinegars were mixed separately with spirit vinegar and diluted synthetic acetic acid (4%) at 1-50% (v/v) ratios. Spectra of vinegars and mixtures were obtained with UV-visible and Fourier-transform infrared (FTIR) spectrometers. Data were evaluated with various chemometric methods and artificial neural networks (ANN). Correct classification rates of at least 94.3% and higher values were obtained by the evaluation of both spectroscopic data along with their combination with chemometric methods and ANN for discrimination of non-adulterated and adulterated vinegars. UV-vis and FTIR spectroscopy can be rapid and accurate ways of detecting adulteration in vinegars regardless of adulterant type.
... Hydrogenation reactions, hydrogen release, and H 2 purification have led to new potential roles for formic acid [13]. Similarly, acetic acid is usually produced by the fermentation of grapes along with wheat, corn, wine, and sugars derived from sugar cane and fruits [14]. In order to understand the constituents which make up vinegar, it is necessary to have a good understanding of the upstream production process. ...
Concerns over the potential adulteration of commercially produced foods give rise to a requirement for a simple and fast analytical method capable of quantifying potential adulterants. This work demonstrates a simple HPLC method tailored to detect major organic acids and furans within ingredients in commercial food products, for example, pomegranate molasses, balsamic vinegar, and apple cider vinegar. The relative importance of this method is in its simplicity and its use of an environmentally friendly aqueous mobile phase under isocratic conditions, providing results in a less than 20 min runtime. The chromatographic separation was achieved using an Acclaim® OA, 5 µm, 120 Å (4.0 × 250 mm) column; a UV-DAD detector set at 210 nm; and a 200 mM Na2SO4 mobile phase with 0.55 mL/L methanosulfonic acid as a pH modifier. The method was then validated by quantifying the concentration of acetic acid, formic acid, citric acid, and hydroxymethyl furfural (HMF) in pomegranate molasses, balsamic vinegar, and apple cider vinegar commercial products. The concentration of acetic acid and HMF in balsamic vinegar was 80.380 mg/mL (±1.272 mg/mL) and 2.153 mg/mL (±0.021 mg/mL), respectively. The apple cider vinegar was composed only of acetic acid with a concentration of 44.139 mg/mL (±0.053 mg/mL). The concentrations of citric acid and HMF were 123.425 mg/mL (±2.502 mg/mL) and 11.382 mg/mL (±0.582 mg/mL), respectively, in pomegranate molasses. Furthermore, this method is also capable of determining various organic acids and furans in biomass: levulinic acid, formic acid, furfurals, diformylfuran, and gamma-valerolactone.
... Other technological advances for vinegar authentication, especially for high-value premium vinegars, include the use of site-specific natural isotopic fractionation by nuclear magnetic resonance (SNIF-NMR) (Consonni et al., 2008;Gregrova et al., 2012;Hsieh et al., 2013) and gas chromatography equipped with isotope ratio mass spectrometry (GC-IRMS) (Hattori et al., 2010;Gregrova et al., 2012). The isotope ratio of a compound of a product from a different geographical origin differs, even for the same product. ...
... Previous studies have shown that C and H stable isotope ratios have a marked capacity to distinguish C3-and C4-derived products, allowing the adulteration of must with raw fermentation materials cheaper than those declared on the label to be detected. [26][27][28][29][30] Natural ratios of 13 Our study confirms the ability of isotopic analysis to detect the fraudulent addition of beet and cane sugar, either added to or in place of the must used to produce ABMs. As shown in Figure For an ABM residue after acetic acid extraction, which can be assimilated to a must, this general reference can be adopted. ...
‘Aceto Balsamico di Modena’ (ABM) is a PGI (Protected Geographical Indication) salad dressing obtained from cooked and/or concentrated grape must, with the addition of wine vinegar and a maximum of 2% caramel (EU Reg. 583/2009).
In this study we investigated whether the combination of ¹³C/¹²C of ethanol using Isotope Ratio Mass Spectrometry with ²H‐site‐specific Natural Isotope Fractionation ‐ Nuclear Magnetic Resonance, and minor sugars using Ion Chromatography with Pulse Amperometric and Charged Aerosol Detection, is able to improve detection of sugar addition to ABM must.
A large selection of authentic Italian grape musts and different samples of balsamic vinegar with an increasing percentage of added beet, cane and sugar syrups were considered.
The possible degradation of sugars in the ABM matrix during shelf life was also investigated.
While stable isotope ratios analysis remains the favoured method for determining cane and beet sugar addition, dosage of minor sugar (in particular maltose) proved to be very useful for detecting the addition of sugar syrup.
Thanks to this innovative approach, 3 out of 27 commercial ABMs were identified as adulterated.
A combination of stable isotope ratio and IC‐PAD‐CAD analysis can be therefore proposed as a suitable tool for detecting the authenticity of ABM must.
... The most plausible reason for this behavior could be deviation from the traditional preparation of this cask series in terms of raw material, such as the use of mixtures of concentrated musts and wine vinegars of different geographical origins and/or varietals. This consideration is also supported by the evidence that the upper interquartile limit lies outside the above mentioned interval for vine plants, highlighting the hypothesis that some glycerol is derived from sugars of exogenous origin (Hattori et al., 2010). ...
The gas chromatographic-combustion-isotopic ratio mass spectrometry (GC-C-IRMS) approach was applied to determine the compound-specific ¹³C/¹²C isotopic ratio of glycerol in balsamic vinegars of Modena (Italy). In particular, Italian Protected Designation of Origin and Protected Geographical Indication balsamic vinegars, namely the traditionally made Aceto Balsamico Tradizionale di Modena (ABTM) and the industrial Aceto Balsamico di Modena (ABM) products, were analyzed and a first attempt at classification was carried out. The carbon isotopic ratio of the glycerol polyalcohol varies on the basis of origin, varietal or provenance; therefore the discriminating potentiality of this species might be useful to elucidate the balsamic vinegar production process. To do this, a preliminary study was conducted and several marketable products, ABTM and ABM type, were subjected to measurements in addition to samples coming from three ABTM cask series (batteria). Experimental results highlighted the peculiarities of the two different production processes, suggesting the use of the carbon isotopic ratio of glycerol as an additional tool for balsamic vinegar authentication.
... Oliveira [38] 测定巴西的鸡胸脯肉和鸡腿肉的 δ 13 C 值和 [39] 采用 13 C 和 14 N 作为内标标 记化合物[1, 2-13 C, 14 N]-SEM 研究出检测鸡蛋中的呋 喃西林代谢物的方法。 董丹 [40] 等以稳定碳同位素 ( 13 C- [54] 用 SCIRA 测定 122 种烈酒和其中 9 种 发酵底物的 δ 13 C 值，建立了根据酒的 δ 13 C 值推断发 酵底物来源的方法：δ 13 C 值范围在-23.4‰ ~ -26.0‰ 则发酵底物为 C3 植物，在-10.3‰ ~ -11.8‰则发酵底 物为 C4 植物。同时得出稳定碳同位素可应用于检测 威士忌是否有外源糖浆或葡萄酒的掺杂。钟其顶 [55] 通 过 GC-C-IRMS 方法测定 43 个固态法白酒(从白酒厂 获得的传统工艺白酒)和 24 个流通领域白酒(从市场 购买的疑似采用固液法新工艺生产的白酒)中的一些 组分的 δ 13 C 值，发现这两类样品中乙醇、异戊醇和乙 酸乙酯的 δ 13 C 存在显著差异， 并且在后续的添加玉米 酒精模拟试验中，验证了该方法的可行性。程涛 [56] 等 利用 EA-IRMS 测定梨白兰地原料中糖的 δ 13 C 值，发 酵后用 GC-C-IRMS 分析乙醇中 δ 13 C 值。结果显示糖 与乙醇的 δ 13 C 值具有良好的线性正相关关系。 模拟实 验表明， 乙醇 δ 13 C 值与玉米酒精含量和蔗糖含量成正 相关关系，因此碳稳定同位素技术可作为检测白兰地 中 C4 来源的酒精或发酵底物中 C4 糖掺假的鉴别手 段。 2.3.2 醋酸 醋酸根据其生产工艺可粗分为发酵醋酸和合成 醋酸。C4 植物来源的醋酸 δ 13 C 值为-11‰ [57] ，而化学 合成的醋酸 δ 13 C 值为-34‰。Hattori [58] 使用顶空-固相 萃取(HS-SPMES)与二维气相色谱-同位素比质谱仪 (GC-Py-GC-C-IRMS)测定了日本的 14 种食醋中醋 酸的 δ 13 C 值。他发现以植物为生产原料的发酵食醋 中，同一醋酸分子中甲基碳原子的 13 C 比羰基碳原子 的 13 C 更容易发生分馏，并且 Δδ 13 C 羰基 -甲基的数值分布 在 0.3~18.2‰的范围，其中来源于 C3 植物为 2.1‰ ~ 6.7‰，来源于 C4 植物为 11.6‰，来源于 CAM 植物 为 18.2‰。 2.3.3 商品油 SCIRA 作为一种强有力的工具在油脂掺假检测 中得到了广泛运用。Woodbury [59] 证明了可通过稳定碳 同位素技术检测玉米(C4 植物)油的掺杂，并建立了 多种植物油掺杂的稳定碳同位素指标。 Kelly [60] 多种纯 植物油进行研究，通过内部参考(in-house reference materials)和内标法监测其 δ 13 C 值，发现两种方法的 检测结果一致： C3 植物油的脂肪酸 δ 13 C 值落在-27.6‰ ~ -32.1‰区间，并建立了产自欧洲的常见植物油稳定 碳同位素判识标准。Woodbury [61] 利用 GC-C-IRMS 测 定了部分市售植物油中主要脂肪酸的 δ 13 C，发现脂肪 酸的 δ 13 C 值也可应用于植物油溯源， 并且， 全油的 δ 13 C 值与脂肪酸的 δ 13 C 值之间有细微的差别， 他们进一步 用胰脂肪酶水解并纯化回收三酰甘油的脂肪酸，分别 对 1、3 位和 2 位脂肪酸的 δ 13 C 进行测定，发现三酰 甘油所有位置上的脂肪酸 δ 13 C 值完全一样。并且，可 通过量化 2 位上的脂肪酸并结合全油和主要脂肪酸的 δ 13 C 值对油的品质进行有效评估。Angerasa [62] 建立了 产自地中海沿岸的橄榄油稳定碳同位素判识标准， Portarena [63] 进一步测定了意大利不同产地的 387 份橄 榄油 δ 13 C 值和 δ 18 O 值，发现这两组数值呈显著正相 关，并且都随着纬度和降水量呈负相关，和温度呈正 相关，δ 13 C 值还和经度呈正相关。他们推测，由于气 孔的开合程度影响大气中二氧化碳的固定和水的蒸 发，进而影响 13 C 的光合作用歧化和 18 O 的富集分馏。 在纬度高的北方，降雨大温度低，所以气孔关闭，所 以 δ 13 C 值和 δ 18 O 值偏低。因而可考虑综合利用 δ 13 C 值和 δ 18 O 值对橄榄油进行溯源。 因植物油的 δ 13 C 值受地区因素的影响， 国外数据 [64] 不能直接套用于我国，我国学者也运用稳定碳同位 素技术对各类食用油进行了研究：郭莲仙 [65][66] 对中国 大陆灵芝孢子油和 12 种植物油的脂肪酸和稳定碳同 位素比值做了系统的研究，建立了中国部分食用油的 脂肪酸和稳定碳同位素判识标志；金青哲 [67] 提出可利 用花生油和玉米油之间三种脂肪酸(C 16:0 , C 18:1 , C 18:2 ) δ 13 C 值的差异去检测花生油的掺杂情况。同样，他们 还测定了棕榈油的脂肪酸，获得其 δ 13 C 值以鉴别掺 杂。 Liu [68] 通过测定 C3 植物油， 动物油和泔水油的 δ 13 C 值和 C 14 /C 18 脂肪酸的比值，发现他们的 δ 13 C 值存在 显著差异： C3 植物油的 δ 13 C 值落在-37.7‰ ~ -27.0‰， 动物油的 δ 13 C 值落在-28.3‰ ~ -14.3‰， 泔水油的 δ 13 C 值落在-25.9‰ ~ -24.1‰。 并且， 联合 δ 13 C 值和 C 14 /C 18 脂肪酸的比值作散点图可区分清洁商品油和泔水油。 2.4 功能性食品 在我国，稳定碳同位素技术逐渐渗透到功能性食 品的掺杂和溯源检测中。 郭莲仙 [69] 通过 EA-IRMS 对 8 种冬虫夏草替代品和冬虫夏草子座样品的 δ 13 C 值进 行了测定，发现不同冬虫夏草替代品和冬虫夏草样品 的 δ 13 C 值存在明显差异。Li [70] 通过 EA-IRMS 等测定 了产自中国 7 个省份的 96 份五味子的 δ 13 C 值，发现 可根据该数值将产地划分为两大块，并且五味子 δ 13 C 值随着纬度的增加而增加， 他们还提出 δ 13 C 值可联合 微量元素或其他同位素将有可能可以作为溯源的指 标。Zhang [71] 利用 EA-IRMS 测定了产自中国 7 个省份 的 49 份茶叶的 δ 13 C 和 δ 15 N 值， 发现 δ 13 C 值随着不同 地区的变化，另外联合应用 δ 13 C 值、δ 15 N 值、微量元 素或其他同位素将有可能茶叶原产地进行溯源。洗燕 萍 [72] ...
Due to the fractionation of stable carbon isotopes in plant photosynthesis, stable carbon isotope ratio analysis (SCIRA) can be used to detect food adulteration during different photosynthetic pathways. Meanwhile, climatic or geographic factors also affect stable carbon isotope fractionation, and can therefore be explored as individual traceability indicators or in combination with other factors. Fractionation patterns of stable carbon isotopes within the same molecule can be produced via different decomposition reactions, which can be measured using specific natural isotope fractionation of nuclear magnetic resonance (SNIF-NMR). In addition, stable carbon isotopes can be used as a marker to determine the veterinary drug residues by isotope dilution mass spectrometry (IDMS). Thus, stable carbon isotope technique can be effectively used in the detection of food adulteration and food traceability. Here, current status of research regarding stable carbon isotopes in the detection of food adulteration and traceability was reviewed, highlighting potential applications of this technique to help improve the current food detection techniques in China. © 2016, Editorial Board of Modern Food Science and Technology. All right reserved.
... The HS-SPME-GC-C-IRMS procedure for the determination of δ 13 C Bulk values is described elsewhere. [19] Briefly, an aliquot of acetic acid or sodium acetate was diluted with saturated saline water to about 0.2 mmol/L and adjusted using HCl to a pH of 2, checked using a pH meter (TPX-90i, Tokyo Chemical Laboratories Co., Ltd, Tokyo, Japan). The 10 mL solutions were enclosed in 20 mL SPME vials (Gerstel GmbH and Co. KG, Mülheim, Germany). ...
RATIONALERecent advances in analytical techniques for the intramolecular carbon isotopic ratio measurement of some organic compounds have provided important information on carbon cycles in biochemistry, organic geochemistry and food chemistry. These advances have made it necessary to prepare intramolecular isotopic reference materials (RMs) to use for inter-laboratory calibration and/or inter-calibration among different analytical methods.METHODS
We evaluated the feasibility of preparing RMs using commercially available reagents for intramolecular carbon isotopic ratio measurement of acetic acid. The intramolecular carbon isotopic distribution of nine acetic acid and four sodium acetate reagents was determined with high precision using off-line pyrolysis combined with gas chromatography–combustion–isotope ratio mass spectrometry (GC-C-IRMS). We also evaluated the potential alteration in the isotopic signature of acetic acid reagents by evaporation.RESULTSThe intramolecular carbon isotopic distributions for the acetic acid and sodium acetate reagents were determined with a precision of better than 0.45‰. We found that the isotopic values of these reagents spanned the carbon isotopic range of acetic acid in biological and environmental samples. We also found that the isotope fractionation associated with the evaporation of acetic acid occurs solely on the methyl position, the carboxyl position being unaffected.CONCLUSIONS
These commercially available reagents will be used as RMs in the future for inter-laboratory calibration and/or inter-calibration with another intramolecular isotopic measurement technique, namely quantitative 13C NMR. In cases where acetic acid is being used as a RM, its storage must be carefully controlled to prevent evaporation. Copyright © 2014 John Wiley & Sons, Ltd.
... To verify it we measured d 13 C in obtained CO 2 from two other vinegars and we obtained the following values: À21.46‰, À19.45‰. Those results are in good agreement with d 13 C values measured in vinegars by Hattori et al. (2010). Therefore, from the point of view of 14 C measurements the fractionation does not cause significant error. ...
This article presents a method of carbon extraction from vinegar used in preparation of liquid scintillation counting cocktails for measurements of low (14)C radioactivity. The presented method is relatively fast and can be used to produce liquid scintillation cocktails e.g., via benzene synthesis. In this work we present specific radiocarbon radioactivity determinations and based on them estimation of bio product content for five commercially available vinegars. All investigated vinegars are likely produced from plants in fermentation process.
... The applications of stable isotope analysis to this kind of product have mainly concerned the use of SNIFeNMR (Site-specific Natural Isotopic FractionationeNuclear Magnetic Resonance), much of the time in combination with 13 C-IRMS (Isotope Ratio Mass Spectrometry) (Boffo & Ferreira, 2006;Krueger, 1991;Remaud, Guillou, Vallet, & Martin, 1992;Thomas & Jamin, 2009). More recently, Hattori et al. (2010) developed a method for measuring the hydrogen and carbon isotope ratio of acetic acid using head space solid-phase microextraction (HS-SPME) combined with gas chromatographyehigh temperature conversion or combustion-isotope ratio mass spectrometry (GCeTC/C-IRMS). In all these studies, carbon and hydrogen isotopic parameters have shown a marked capacity to identify synthetic vinegars and distinguish C3 and C4 derived products, allowing detection of vinegars adulterated with raw fermentation materials cheaper than those declared on the label. ...
Production of wine vinegar by fermenting dried grapes and rehydrating with tap water is not allowed by European Regulations. In this study we proved experimentally that δ18O analysis of beverage water, officially used to detect the watering of wine and rehydration of concentrated fruit juice, can also be applied to vinegar to detect this kind of fraud. We considered fourteen production chains from wine to the corresponding raw vinegar and diluted vinegar (6% of acidity), and the official European wine databank established according to EU Reg. 555/2008. δ18O limit values of −2‰ and −5‰ were defined for raw and diluted vinegars produced from fresh grapes. Values lower than these limits indicate a significant addition of water to a starting matrix with a sugar concentration much higher than fresh grapes. On this basis, more than 60% of 92 suspicious wine vinegars imported to the Italian market were shown not to be authentic, but rather obtained by diluting a concentrated source such as dried grapes with water.
... These include paleoclimate and paleoenvironmental research, [2][3][4][5] biogeochemistry, [6][7][8][9] environmental research, including hydrogen compound specific isotope analysis of n-alkanes in petroleum crudes, hydrogen isotopic fractionation due to evaporation, degradation, GC oven programs, [10][11][12][13][14][15][16] atmospheric chemistry, [17,18] and food research. [19][20][21] Due to the very low abundance of 2 H (0.015%) in nature, high accuracy and precision are necessary for highresolution research and routine isotopic analysis. ...
The condition of the pyrolysis reactor is very important for obtaining stable, precise hydrogen isotopic ratios using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC/TC/IRMS). However, few studies of the conditioning process have been conducted, and little is known about the best methods for high-precision hydrogen isotope analysis.
We investigated δ(2) H variations and observed the changes in carbon coating using six different conditioning methods for the pyrolysis alumina tube: (i) no treatment; (ii) conditioning with 4 μL hexane; (iii) conditioning with 2 μL hexane; (iv) conditioning with 2 μL hexane followed by backflushing overnight; (v) conditioning with 10 s of backflushing with methane; (vi) conditioning with 3 s of backflushing with methane.
Conditioning the alumina tube can improve the pyrolysis efficiency of organic compounds because a moderate amount of carbon acts as a catalyst in high-temperature regions of the alumina tube. Carbon actually flows in the tube and is difficult to confine to the high-temperature region. Insufficient amounts of carbon in the high-temperature regions lead to incomplete pyrolysis of organic compounds and lower δ(2) H values due to kinetic fractionation of hydrogen isotopes. In contrast, excess hexane or methane can lead to higher δ(2) H values, probably due to enrichment of deuterium in the hydrocarbon residue.
The δ(2) H values obtained by Method 6 are closest to the TC/EA δ(2) H values and are more precise than those obtained by other methods, perhaps because this method introduces a moderate, consistent amount of carbon with each sample injection. Copyright © 2012 John Wiley & Sons, Ltd.
... Methane and acetate were determined by gas chromatograph GC-14B (Shimadzu) and 2 was determined by gas chromatograph GC-14C (Shimadzu) [8,40]. The stable isotope composition was determined by Trace GC/IsoLink/Delta V Advantage GC/IRMS (Thermo Fisher Scientific, Bremen, Germany) [41,42]. Table S1 The primers used in this study. ...
In this work, we report the complete genome sequence of an obligate aceticlastic methanogen, Methanosaeta harundinacea 6Ac. Genome comparison indicated that the three cultured Methanosaeta spp., M. thermophila, M. concilii and M. harundinacea 6Ac, each carry an entire suite of genes encoding the proteins involved in the methyl-group oxidation pathway, a pathway whose function is not well documented in the obligately aceticlastic methanogens. Phylogenetic analysis showed that the methyl-group oxidation-involving proteins, Fwd, Mtd, Mch, and Mer from Methanosaeta strains cluster with the methylotrophic methanogens, and were not closely related to those from the hydrogenotrophic methanogens. Quantitative PCR detected the expression of all genes for this pathway, albeit ten times lower than the genes for aceticlastic methanogenesis in strain 6Ac. Western blots also revealed the expression of fwd and mch, genes involved in methyl-group oxidation. Moreover, (13)C-labeling experiments suggested that the Methanosaeta strains might use the pathway as a methyl oxidation shunt during the aceticlastic metabolism. Because the mch mutants of Methanosarcina barkeri or M. acetivorans failed to grow on acetate, we suggest that Methanosaeta may use methyl-group oxidation pathway to generate reducing equivalents, possibly for biomass synthesis. An fpo operon, which encodes an electron transport complex for the reduction of CoM-CoB heterodisulfide, was found in the three genomes of the Methanosaeta strains. However, an incomplete protein complex lacking the FpoF subunit was predicted, as the gene for this protein was absent. Thus, F(420)H(2) was predicted not to serve as the electron donor. In addition, two gene clusters encoding the two types of heterodisulfide reductase (Hdr), hdrABC, and hdrED, respectively, were found in the three Methanosaeta genomes. Quantitative PCR determined that the expression of hdrED was about ten times higher than hdrABC, suggesting that hdrED plays a major role in aceticlastic methanogenesis.
Rationale
Vinegar is an everyday condiment made from fermented grains or fruits. It contains acetic acid which is the main organic material produced by fermentation. Vinegar suffers from the authenticity problem of exogenous adulteration due to the indistinguishability of low‐cost chemical sources of synthetic acetic acid from acetic acid produced by fermentation. It is necessary to establish a simple and rapid measurement technique.
Methods
Determination was according to the total acid content of vinegar diluted with acetone to a certain concentration. Online separation and determination of acetic acid δD in vinegar were carried out using gas chromatography–pyrolysis–isotope ratio mass spectrometry.
Results
An HP‐Plot/U column was selected for online separation of acetic acid and water with molecular sieve characteristics. At the same time, combined with the instrument blowback function to remove water. Dilute solvent acetone was treated with a molecular sieve to remove trace water. The reproducibility of this method is less than 3‰. The long‐term stability is within a reasonable error range. The accuracy correlation coefficient is greater than 0.99. The δD values of acetic acid in vinegar (−264.5 ± 20.3‰) and from chemical sources (−30.5 ± 90.8‰) were obtained.
Conclusions
A rapid method was developed for identification of different sources of acetic acid. These different sources of acetic acid exhibited significant hydrogen isotope distribution characteristics. Additionally, it was observed that the carboxyl hydrogen of acetic acid exhibited facile exchange with water. In future investigations, we aim to mitigate this interference.
E-150d caramel, known as grape-must caramel in the vinegar industry, may be added legally and without restriction to balsamic vinegar to improve the final color. Although its quantification in vinegar was studied with other techniques, a straightforward and quick method is lacking. Hence, the inner filter effect (IFE) was proposed to be mediated by concentration-dependent Laser-induced fluorescence (LIF) intensity and could be used to quantify caramel in balsamic vinegar.
Vinegar is a very popular condiment with different species and aroma profiles. Eighty-three volatile odor compounds (VOCs) were identified from European vinegar using ultra-fast gas chromatographic electronic nose (UFGC E-nose), of which there were 61 VOCs with odor activity value (OAV) ≥1. Among the 61 VOCs, acetic acid, ethyl isovalerate, propionaldehyde, butanoic acid, ethyl cinnamate, and guaiacol contributed significantly to the aroma property and type of European vinegar. There were obvious clustering trends of apple vinegar, wine vinegar, and balsam vinegar in principal component analysis (PCA). The clustering of the vinegar-like groups was more obvious in orthogonal partial least squares discriminant analysis (OPLS-DA). The volatile markers discriminating vinegar, including acetic acid, propionic acid, pyrazine, furfural, isopropyl alcohol, and so on, were screened out by variable importance for the projection (VIP). These results demonstrated that UFGC E-nose is a novel, rapid and non-destructive analytical tool and can also be used for identifying aroma compounds and tracing the food species.
La datation par la méthode du radiocarbone fait partie des méthodes d’analyse utilisées en archéologie et histoire de l’art pour déterminer l’âge d’un objet constitué de matériaux issus d’organismes vivants. Aujourd’hui, dans le domaine des arts, et en particulier dans celui de la peinture, les constituants d’une œuvre peinte accessibles à cette technique sont les supports en bois, en toile ou papier et, depuis peu, les liants d’origine végétale ou animale. Cependant, le résultat provenant des supports ne reflète pas toujours la date de réalisation de l’œuvre en raison du réemploi habituel de ces matériaux. Le liant n’est, quant à lui, pas toujours organique ni présent en quantité suffisante. Trouver d’autres matériaux du peintre datables par 14C est donc d’importance pour authentifier une œuvre picturale. À l’exception du noir de carbone issu du charbon de bois ou d’os, la plupart des autres constituants des couches de peintures semblent inappropriés car il s’agit, généralement, de pigments inorganiques extraits de minerais naturels et dépourvus en 14C.Le blanc de plomb est un pigment qui a été très largement utilisé de l’Antiquité jusqu’au tout début du 20ème siècle. L’étude des mécanismes de sa synthèse a récemment mis en évidence le rôle du dioxyde de carbone dans la formation des deux carbonates de plomb (cérusite et hydrocérusite) qui le compose. Ainsi, l’incorporation de carbone lors de la production du blanc de plomb fait de lui un potentiel candidat pour la datation radiocarbone et pour l’authentification des œuvres peintes.Ce travail de thèse a consisté à mettre en place les protocoles expérimentaux pour la mesure des isotopes du carbone (13C et 14C) dans les pigments et peintures à base de blanc de plomb afin de tester cette hypothèse. Un protocole d’extraction du carbone des carbonates de plomb a été développé et adapté à la nature et à la complexité des matériaux étudiés, pigment brut ou chargé et peinture. L’étude s’appuie sur les propriétés de décomposition thermique des carbonates de plomb et permet de déterminer les meilleures conditions d’extraction du carbone. La méthode a ensuite été éprouvée et validée sur un large panel d’échantillons modèles et d’échantillons historiques d’âge connu. De plus, les données isotopiques du carbone ont été mises en relation avec les recettes historiques et ont permis de discriminer les différents procédés de production du blanc de plomb.Cette thèse a permis de démontrer que le blanc de plomb est un pigment inorganique datable par la méthode du radiocarbone : la mesure 14C fournit alors sa date de fabrication. La démarche et les protocoles présentés pour cette étude pourraient également être adaptés à d’autres pigments inorganiques de peinture contenant du carbone organique, augmentant ainsi le nombre de matériaux disponibles pour la datation et l’authentification du patrimoine pictural.
In this study, we developed a method to simultaneously measure the stable carbon isotope ratio for acetic acid (δ 13Cacetic acid) and acetoin (δ13Cacetoin) in rice vinegar by gas chromatography-combustion-isotope ratio mass spectrometry. The method showed good precision and accuracy. With this method, data from 16 brewed rice vinegars and 10 acetic acid samples were used to evaluate the feasibility of adulteration detection. On the basis that all δ13Cacetoin values of brewed rice vinegars are nearly constant, a characteristic pattern of the stable carbon isotope in rice vinegar was built with the 95% confidence intervals for δ13Cacetic acid (-26.97 to -25.38‰), δ13Cacetoin (-28.14 to -27.09‰), and Δδ13C (0.61 to 2.27‰). An adulteration detection curve of Δδ13C was proposed based on the results of vinegar and acetic acid samples and confirmed by vinegar spiked with different amounts of acetic acid. This method could be useful in estimating the blending ratio of adulterated rice vinegar products. Products containing more than 10% of synthetic acetic acid could be possibly identified.
A holistic and comparative quality assessment of vinegars from different countries is needed with international trade of vinegar become frequent. In this study, compounds characterization and comparison of commercial-grade Chinese cereal and European grape vinegars were performed using 1H NMR spectroscopy coupled with principal component analysis (PCA) and orthogonal projection to latent structures discriminate analysis (OPLS-DA). The results showed that Balsamic vinegars of Modena were clearly discriminated by higher amount of fructose and glucose, while Chinese aromatic vinegar and aged vinegars were characterized by higher amount of amino acids, volatile compounds, succinate and betaine. On the other hand, flavoring compounds in Chinese rice vinegar and European wine vinegars are less than the others. These characteristic components are associated with the special raw materials and producing process of each types of vinegar and endow them special flavor. The results obtained in this study provide a global insight into vinegar through a 1H NMR based compounds analysis that allows a holistic quality assessment and comparison of vinegars from different manufacture origins.
There were evaluated potentialities of sensory analysis, analysis of the profile and content of volatile compounds and isotopic analysis of the ratios of 13C/12C a 2H/1H to prove the spirit vinegars adulteration realized by adding synthetic acetic acid. A set of 14 samples of spirit vinegars produced by Central European producers and synthetic acetic acids was analysed. Sensory evaluation and content determination of characteristic volatile markers of fermentation (ethanol and ethylacetate) allowed us to distinguish spirit vinegar and synthetic acetic acid solutions; but in the case of mixtures neither of the methods provided statistically significant results. Isotope analysis has been confirmed as a suitable tool for assessing the authenticity of vinegar, but it is relatively expensive and instrumentally demanding technique which enables reliable detection of synthetic acetic acid addition into the spirit vinegars above 15 %.There were evaluated potentialities of sensory analysis, analysis of the profile and content of volatile compounds and isotopic analysis of the ratios of 13C/12C a 2H/1H to prove the spirit vinegars adulteration realized by adding synthetic acetic acid. A set of 14 samples of spirit vinegars produced by Central European producers and synthetic acetic acids was analysed. Sensory evaluation and content determination of characteristic volatile markers of fermentation (ethanol and ethylacetate) allowed us to distinguish spirit vinegar and synthetic acetic acid solutions; but in the case of mixtures neither of the methods provided statistically significant results. Isotope analysis has been confirmed as a suitable tool for assessing the authenticity of vinegar, but it is relatively expensive and instrumentally demanding technique which enables reliable detection of synthetic acetic acid addition into the spirit vinegars above 15 %.
The natural carbon isotopic composition of acetone in urine was measured in healthy subjects using gas chromatography–combustion–isotope ratio mass spectrometry combined with headspace solid-phase microextraction (HS-SPME–GC–C–IRMS). Before applying the technique to a urine sample, we optimized the measurement conditions of HS-SPME–GC–C–IRMS using aqueous solutions of commercial acetone reagents. The optimization enabled us to determine the carbon isotopic compositions within ±0.2 ‰ of precision and ±0.3‰ of error using 0.05 or 0.2 mL of aqueous solutions with acetone concentrations of 0.3–121 mg/L. For several days, we monitored the carbon isotopic compositions and concentrations of acetone in urine from three subjects who lived a daily life with no restrictions. We also monitored one subject for 3 days including a fasting period of 24 h. These results suggest that changes in the availability of glucose in the liver are reflected in changes in the carbon isotopic compositions of urine acetone. Results demonstrate that carbon isotopic measurement of metabolites in human biological samples at natural abundance levels has great potential as a tool for detecting metabolic changes caused by changes in physiological states and disease.
Graphical abstract
The natural carbon isotopic composition of acetone in urine can be determined using HS-SPME-GCC-IRMS and can provide information on changes in the availability of glucose in the liver.
RationaleHeadspace solid-phase microextraction (HS-SPME) combined with gas chromatography/pyrolysis-gas chromatography/combustion-isotope ratio mass spectrometry (GC/Py-GC/C-IRMS) was developed for the simultaneous determination of the intramolecular and molecular carbon-isotopic composition (C-13 value) of acetic acid. Methods
The C-13 values of carboxyl and methyl carbon were standardized using calibration curves constructed from the regression between the measured C-13 values and the C-13 values of working standards determined in a previous study. We applied this developed HS-SPME-GC/Py-GC/C-IRMS technique to commercial vinegars. ResultsIn one injection analysis, the bulk and intramolecular C-13 values of pure acetic acid standards can be obtained. The repeatability (1 sigma) of the bulk C-13 values is within 0.4 parts per thousand, and that of the C-13(carboxyl) and C-13(methyl) values is within +/- 0.6 parts per thousand. The intramolecular C-13 values of acetic acid in vinegars exhibit a similar pattern. The average value (C-13(COOH) - C-13(CH3)) is 4.3 +/- 2.0 parts per thousand. Conclusions
The approach presented herein for the molecular and intramolecular C-13 determination of acetic acid avoids switching between configuration systems and thereby reduces systematic errors. It is expected to be useful for examining isotope fractionation associated with processes related to organic acid (bio)transformations. Copyright (c) 2015 John Wiley & Sons, Ltd.
Stable carbon isotope composition (δ13C) of acetic acid is a valuable character as tracer for raw fermentation material of vinegar, however, the analytical technique still remains be estimated. Now, a rapid method for the determination of δ13C of acetic acid in vinegar by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) coupled with a capillary column was developed. Results demonstrate that the method above is stable with a standard deviation (1σ) lower than 0.15‰ (n=16) with which other organic compounds in vinegar can be ignored, and the variation of δ13C determination is very small while acetic acid range from 2% to 99.9%. We take participant in a FIT Proficiency Testing Scheme for an inter-laboratory comparison study of carbon isotopic methods of acetic acid, and the difference is 0.17‰ between the measurement and the mean value of 5 laboratories. This method has an advantage of easy and rapid operating, and which is applicable for δ13C analysis of acetic acid for vinegar authenticity control. ©, 2014, Journal of Chinese Mass Spectrometry Society. All right reserved.
The natural xanthines caffeine, theobromine and theophylline are of major commercial importance as flavor constituents in coffee, cocoa, tea and a number of other beverages. However, their exploitation for authenticity-a requirement in these commodities that have a large origin-based price-range-by the standard method of isotope ratio monitoring by mass spectrometry (irm-MS) is limited. We have now developed a methodology that overcomes this deficit that exploits the power of isotopic quantitative 13C nuclear magnetic resonance (NMR) spectrometry combined with chemical modification of the xanthines to enable the determination of positional intramolecular 13C/12C ratios (δ13Ci) with high precision. However, only caffeine is amenable to analysis: theobromine and theophylline present substantial difficulties due to their poor solubility. However, their N-methylation to caffeine makes spectral acquisition feasible. The method is confirmed as robust, with good repeatability of the δ13Ci values in caffeine appropriate for isotope fractionation measurements at natural abundance. It is shown that there is negligible isotope fractionation during the chemical N-methylation procedure. Thus, the method preserves the original positional δ13Ci values. The method has been applied to measure the position-specific variation of the 13C/12C distribution in caffeine. Not only is a clear difference between caffeine isolated from different sources observed, but theobromine from cocoa is found to show a 13C pattern distinct from that of caffeine.
抄録
The elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) has become increasingly important as a potential powerful tool for food authenticity. However, the lack of a reliable technique for the isotope ratio measurement, and limited availability of adequate international references are significantly regrettable, and should be improved immediately. Here we present results of an inter-laboratory test on the EA-IRMS determination of stable carbon, nitrogen and oxygen isotopic compositions (δ¹³C, δ¹⁵N and δ¹⁸O) in organic compounds. Three organic compounds (L-alanine for δ¹³C and δ¹⁵N, and 1,2,3,4,6-penta-O-acetyl-α-D-glucopyranose and Dimethyl aminoterephthalate for δ¹⁸O) were distributed and analyzed by a total of 25 laboratories. The results show that the 1σ standard deviation among laboratories is −11.9 ± 0.2 ‰ (for δ¹³C), −2.6 ± 0.3‰ (for δ¹⁵N), +32.3 ± 1.0‰ (for δ¹⁸O of the glucopyranose derivative), and +25.9 ± 2.3‰ (for δ¹⁸O of Dimethyl aminoterephthalate). Although the variations of the standard deviations for δ¹³C, δ¹⁵N and δ¹⁸O (glucopyranose derivative) among laboratories are not so large compared to the instrument uncertainties, δ¹⁸O of Dimethyl aminoterephthalate, which contains nitrogen, shows a large variation among laboratories. This may have been caused by much contamination of N2 to the CO peak on the EA-IRMS chromatogram, and may be improved by using a longer GC column (1.0∼1.5 m) for chromatographic separation.
As consumers demand more certainty over where their food and beverages originate from and the genuineness of ingredients, there is a need for analytical techniques that are able to provide data on issues such as traceability, authenticity, and origin of foods and beverages. One such technique that shows enormous promise in this area is gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). As will be demonstrated in this review, GC-C-IRMS is able to be applied to a wide array of foods and beverages generating data on key food components such as aroma compounds, sugars, amino acids, and carbon dioxide (in carbonated beverages). Such data can be used to determine synthetic and natural ingredients; substitution of 1 ingredient for another (such as apple for pear); the use of synthetic or organic fertilizers; and origin of foods and food ingredients, including carbon dioxide. Therefore, GC-C-IRMS is one of the most powerful techniques available to detect fraudulent, illegal, or unsafe practices in the food and beverages industries and its increasing use will ensure that consumers may have confidence in buying authentic products of known origin.
Traditional Taiwanese rice spirits were made from rice, which is their only ingredient and ethanol source. Site-specific natural isotopic fractionation by nuclear magnetic resonance (SNIF-NMR) methods were used to investigate molasses spirits usually mixed in rice spirits. The mean ratios for the parameters in five rice spirits labeled as Taikeng 8, Taikeng 9, Taichung sen 10, Tainan 11, and Tainung 71 were (D/H)I, 99.0–100.3 ppm; (D/H)II, 121.3–123.0 ppm; whereas for molasses spirits labeled as MS, the mean ratios were 108.7 ppm and 126.8 ppm, respectively. A close and reproducible correlation was found for (D/H)I values of the mixtures in which MS was mixed with authentic rice spirit samples. The 3.62% MS mixed in Tainung 71 was detected through calculation, whereas the detectable limit for MS mixed in other rice spirits ranged from 8.20% to 11.73%. The SNIF-NMR analysis provides a powerful method for the detection of rice spirits adulteration and can determine the extent to which the rice spirit product is mixed with MS.
Formic and acetic acid are ubiquitous in the environment and many biological processes. Analysis of the stable carbon isotope composition (δ(13)C) is important to understanding their biogeochemical cycles. It has been, however, faced with poor accuracy and high detection limit due to their low carbon number, high hydrophilicity and semi-volatility. Here we developed an analytical technique by needle trap and gas chromatography-isotope ratio mass spectrometry (GC-IRMS). The organic acids in aqueous solution were extracted using a NeedlEx through purge-and-trap and analyzed by GC-IRMS for δ(13)C. The procedures incur no isotope fractionation. Defined as the point at which the mean δ(13)C is statistically the same as the given value and the analytical error starts rising, the method's detection limit is 200 mg/L and 100 mg/L for formic and acetic, respectively, with an uncertainty about 0.5‰ in direct extraction and analysis. They were lowered to 1 mg/L with precision 0.9‰ after samples were subjected to pre-concentration. The method was successfully applied to natural samples as diverse as precipitation, vinegars, ant plasma and vehicle exhaust, which vary considerably in concentration and matrix of the organic acids. It is applicable to the organic acids in not only aqueous solution but also gaseous phase.
Isotopic (13)C NMR is a relatively recent technique which allows the determination of intramolecular (13)C isotope composition at natural abundance. It has been used in various scientific fields such as authentication, counterfeiting or plant metabolism. Although its precision has already been evaluated, the determination of its trueness remains still challenging. To deal with that issue, a comparison with another normalized technique must be achieved. In this work, we compare the intramolecular (13)C isotope distribution of ethanol from different origins obtained using both Isotope Ratio Mass Spectrometry (IRMS) and Nuclear Magnetic Resonance (NMR) spectrometry techniques. The IRMS approach consists of the oxidation of ethanol to acetic acid followed by the degradation of the latter for the analysis of each fragments formed. We show here that the oxidation of ethanol to acetic acid does not bring any significant error on the determination of the site-specific δ(13)C (δ(13)C(i)) of ethanol using the IRMS approach. The difference between the data obtained for 16 samples from different origins using IRMS and NMR approaches is not statistically significant and remains below 0.3‰. These results are encouraging for the future studies using isotopic NMR, especially in combination with the IRMS approach.
Compound-specific carbon isotope analysis of acetic acid is useful for origin discrimination and quality control of vinegar. Intramolecular carbon isotope distributions, which are each carbon isotope ratios of the methyl and carboxyl carbons in the acetic acid molecule, may be required to obtain more detailed information to discriminate such origin. In this study, improved gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) was used to measure the intramolecular carbon isotope distributions of acetic acid in 14 Japanese vinegars. The results demonstrated that the methyl carbons of acetic acid molecules in vinegars produced from plants were mostly isotopically depleted in (13)C relative to the carboxyl carbon. Moreover, isotopic differences (δ(13)C(carboxyl) - δ(13)C(methyl)) had a wide range from -0.3 to 18.2‰, and these values differed among botanical origins, C3, C4, and CAM plants.
The natural site-specific deuterium content and the overall 13C content of acetic acids, extracted from vinegars or obtained by chemical synthesis, were determined by NMR and mass spectrometries. The isotope ratios (D/H)CH3 and the 13C deviation of these samples were compared to those of a series of ethanols of the same natural or synthetic origins. The different groups of natural and fossil acetic acids are represented in the 2H/13C isotopic plane and the discriminant function, which enables unknown samples to be assigned to a given group, is computed. A careful analysis of the repeatability of the entire analytical procedure and a study of known mixtures of natural and synthetic acids show that as low as 5% synthetic acid in a natural vinegar can be detected in a comparative analysis. A sensitivity level of 15% may be expected on an absolute basis when no information on the origin of the precursors is available, providing that a determination of the botanical family of the natural component can be carried out beforehand.
A pilot study was conducted to evaluate the suitability of multi-element isotope ratio analysis for determining the origin of cows’ milk produced within Australasia. A milk sample from pasture-fed cows was obtained from seven dairying regions in Australia and New Zealand and analysed for the ratios of 13C/12C, 15N/14N, 18O/16O, 34S/32S, and 87Sr/86Sr. Each milk sample displayed a distinct isotopic fingerprint. Isotope ratios for 18O/16O and 13C/12C, in particular, conformed to predicted isotope fractionation patterns based on the latitude and climate of each region. Relative to skim milk, casein was enriched in 13C and 15N, and depleted of 34S, whereas, predictably, 87Sr/86Sr ratios remained equivalent in both skim milk and casein. The milk samples from Australasia were considerably enriched in 18O and 34S compared with reported values for most European dairy products. Overall, multi-element isotopic analysis has good potential for determining the geographic origin of dairy products produced within Australasia.
BSE, first identified in the UK in 1986 is thought to have arisen from feeding scrapie infected Meat and Bone Meal (MBM), produced under sub-optimal conditions, to cattle. For quality and safety reasons there is a requirement for a good analytical test for the surveillance of processed MBM. This study describes species-specific PCR assays for the identification of ovine, porcine and poultry species in MBM. A comparison between two distinct DNA extraction methods, i.e. the silicaguanidiumthiocyanate DNA isolation procedure and a commercial DNA extraction kit, is also presented. Application of this technology to species identification in industrial MBM was investigates as part of this study.
The isotopic investigation of vanillin has been extended to the new sources of natural precursors of vanillin recently introduced with a view of obtaining natural vanillin by biotechnological processes. To check the consistency of the isotopic composition of vanillin with that of the corresponding aromatic fragment, a selective degradation reaction into guaiacol was carried out. The reaction was shown to proceed without significant isotopic fractionation at the sites of interest, and an optimized procedure was defined from the results of an experimental design involving the quantity of reagent and the temperature and duration of the experiment. Guaiacol, which can be easily obtained in a reasonable time, is an interesting isotopic probe for carbon- and oxygen-isotope ratio mass spectrometry (IRMS) determinations. It provides (13)C information specific to the aromatic fragment and, combined with delta(13)C values measured on vanillin itself, it improves the authentication potential of carbon-IRMS. Thus, the natural status of ferulic acid may be characterized by significant (13)C depletion at the formyl site. Similarly, the oxygen-18 content of guaiacol is a better authentication tool than delta(18)O of vanillin because it does not suffer the drawback of being altered by chemical exchange of the sp(2) oxygen atom with water in industrial or laboratory procedures. Although collaborative studies are still necessary to improve the interlaboratory reproducibility of the delta(18)O parameters, consistent results can be obtained in an intralaboratory context. It is shown in particular that chemical oxidation of ferulic acid is characterized by a relative enrichment of the aromatic moiety of vanillin.
Three stable isotope ratios, D/H, (13)C/(12)C and (18)O/(16)O, are measurable in ethanol, an important organic compound that is used as a material for food and beverages, fuel and chemical feedstock, and as a substance related to metabolism. We developed a simple and rapid method of measurement of three isotope ratios of ethanol in aqueous solution at millimole levels using gas chromatography-high-temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) combined with solid-phase microextraction (SPME). Using this method, the delta value for ethanol was determined in 30 min for deltaD and delta(13)C, and in 75 min for delta(18)O with precisions of +/-9 per thousand, +/-0.3 per thousand and +/-0.7 per thousand, respectively, for deltaD, delta(13)C, and delta(18)O. An advantage of this process is that it requires no distillation for ethanol purification. The method is useful for small quantities of analyte with low ethanol concentrations, which is expected for environmental and metabolic studies.
Stable isotope ratio analysis of wine by 2H-SNIF®-NMR, 13C-, and 18O-isotope ratio mass spectrometry are official methods in the European Union for the proof of chaptalization, addition of water, sweetening with sugar, and authentication of geographic origin and year of harvest. By evaluation of stable isotope data of authentic reference wines from the German wine-growing regions Franconia and Lake Constance, Hungary, and Croatia as well as wines which were on the German market, the influence of geographical origin, climate, year and date of vintage, and viticultural aspects (soil water status, water stress, irrigation) on isotope fractionation of 13C, 2H, and 18O in water, sugar, and alcohol are discussed.
A straightforward way of isolating acetic acid from vinegars and pickled preserves and measuring its D/H ratio employing a combination of natural abundance deuterium- and proton NMR-spectroscopy is described. Additionally, an approach for referencing the isotopic ratios to a certified standard material is given. Some results on pickled preserves are presented.
¹³C/¹²C ratios have been determined for plant tissue from 104 species representing 60 families. Higher plants fall into two categories, those with low δPDBI¹³C values (—24 to —34‰) and those with high δ ¹³C values (—6 to —19‰). Algae have δ ¹³C values of —12 to —23‰. Photosynthetic fractionation leading to such values is discussed.
A preliminary study to classify tea by geographical origin using trace metal concentrations was made. Fifteen types of tea from ten different countries were digested using nitric acid. The digests were then analysed for their trace metal contents using either inductively coupled plasma-atomic emission spectrometry for the more concentrated analytes (Al, Ba, Ca, Cu, Fe, La, Mg, Mn, Sr, Ti and Zn) or inductively coupled plasma mass spectrometry for the less concentrated analytes (Cd, Co, Cr, Cs, Hg, La, Li, Nd, Ni, Ph, Pr, Ph, Se, Sn, Ti, V and Zr), The data obtained from these results were then analysed using UNSCRAMBLE, a chemometrics package that incorporates principal component analysis, and by using Matlab 4.2cl High Performance Numeric Computation and Visualisation software. The results of the chemometrics analysis indicated that a distinction between African and Asian and between Chinese and other Asian teas could be made.
Site-specific natural isotope fractionation measured by deuterium NMR (SNIF-NMR) was used for investigating the deuterium transfers occurring in the fermentation of sugars into ethanol. In contrast to carbon-13, which is usually assumed to be randomly distributed within the glucose skeleton, very large deviations with respect to a statistical repartition are determined for deuterium. By transforming glucose samples from different origins into acetates and nitrates, the absolute values of the D/H ratios in the nonexchangeable sites were obtained. The hydroxyl sites were considered to contribute to the isotope content of the starting water medium. The site-specific isotope parameters were determined for more than 50 ethanol samples obtained by fermenting glucose samples issued from different starches and sucroses in water media with different isotope ratios. Several concentrations of sugar, several strains of the same yeast, and different temperatures of fermentation were considered. The whole set of isotope parameters characterizing the nonexchangeable sites of glucose, the starting and end water media, and the methyl and methylene sites of ethanol was submitted to factor analysis. The results are satisfactorily reproduced on the basis of two main factors which may be associated with the independent contributions of the isotope ratios of glucose and water. The isotope parameters of the end products and of the starting materials were then considered to be related by a set of linear equations and the coefficients of the redistribution matrix were calculated by multidimensional analysis. Thus the isotope ratio of the methyl site of ethanol exhibits a strong sensitivity toward the nonexchangeable sites of glucose and depends to a lesser extent on the isotope content of the starting water medium. By contrast, no direct connection is found between glucose and the methylene site which is only sensitive, with a strong discriminating effect against deuterium to the isotope content of water. A redistribution coefficient slightly less than unity (0.96 for a concentration of sugar of 100 g L-1) is found between the isotope ratio of the end and starting water media. Although the bioconversion of glucose into ethanol occurs with high fractionation effects which are the source of high deuterium depletions in the methyl and methylene sites of ethanol as compared to glucose, constant redistribution parameters can be obtained in appropriate conditions and the isotope parameters measured in alcohols may be used as a fingerprint for characterizing the sugar and aqueous juice from which they have been produced. The site-specific natural isotope parameters of ethanol therefore constitute a faithful and powerful probe for investigating the physiological biochemical and climatological effects which have governed the photosynthesis of sugars in natural conditions.
Various chemical methods used to detect contamination in food, and monitoring food quality are presented. The technical improvements in stable isotope-ratio mass spectrometry (IRMS) has led to reduced measurement time, with various results and a number of applications. IRMS provides high reproducibilty, if the samples are converted into simple gases such as hydrogen, carbon dioxide, carbon monoxide, nitrogen, oxygen or sulfur dioxide. High temperature furnaces above 1500°C improve the measurement of organically bound hydrogen and oxygen by using new materials such as silicon carbide. Various sophisticated techniques such as Gas chromatography is used to separate compounds and determine the 13C/12C and 15N/ 14N ratios. Application of nuclear magnetic resonance (NMR) and laser techniques make use of differences between the resonances of the stable isotopes within the molecule.
Solid-phase microextraction (SPME) was used to facilitate the measurement of stable carbon isotope compositions (at natural abundance) of six organic compounds representing four compound classes in aqueous solution. Toluene, methylcyclohexane, hexanol, and acetic, propionic, and valeric acids were extracted from aqueous solutions with appropriate SPME phases and thermally desorbed into the split/splitless inlet of an isotope ratio monitoring gas chromatograph/mass spectrometer (irmGC/MS). Hydrophobic compounds (toluene, methylcyclohexane, hexanol) extracted by a nonpolar SPME phase were slightly (≤0.5‰) enriched in (13)C while organic acids extracted with a polar phase were depleted in (13)C to a somewhat greater degree (≤1.5‰) relative to material remaining in the aqueous phase. Isotopic fractionation was not observed to vary systematically as a function of equilibration time or solute concentration. Further, isotope fractionation did not vary consistently with the partition coefficient (K(fw)). However, both salinity and cosolvent effects, which altered the partition coefficients of the solutes, also yielded a reduction in the magnitude of isotopic fractionation (to ≤0.4‰ for the hydrocarbons, ≤0.5‰ for the organic acids). We conclude that fractionations are most likely associated with the interactions of organic compounds with the organic phase coating SPME fibers and are specifically due to mass-dependent energy shifts upon solution of each analyte into the organic phase. In addition, fractionations are also influenced by energy shifts associated with electrostatic forces acting on the analyte in the water phase during the partitioning process. The magnitude of isotopic fractionations can be minimized under conditions appropriate for the analysis of natural waters, and with careful calibration, SPME and irmGC/MS should be a valuable means for isotopic analyses for a wide range of organic constituents in aqueous samples.
The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages.
The objective of this research was to demonstrate the feasibility of this method to differentiate the geographical growing regions of coffee beans. Elemental analysis (K, Mg, Ca, Na, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, S, Cd, Pb, and P) of coffee bean samples was performed using ICPAES. There were 160 coffee samples analyzed from the three major coffee-growing regions: Indonesia, East Africa, and Central/South America. A computational evaluation of the data sets was carried out using statistical pattern recognition methods including principal component analysis, discriminant function analysis, and neural network modeling. This paper reports the development of a method combining elemental analysis and classification techniques that may be widely applied to the determination of the geographical origin of foods.
Compound-specific carbon isotope analysis (CSIA) has become an important tool in biological, archeological, and geological studies as well as in forensics, food sciences, and organic chemistry. If sensitivity could be enhanced, CSIA would further have an improved potential for environmental applications such as, for example, in situ remediation studies to assess contaminated environments, identification of pollutant degradation pathways and kinetics, distinction between degradation/formation mechanisms, or, verification of contaminant sources. With this goal in mind, we have developed methods to determine delta13C values of commonly reported groundwater contaminants in low-microgram per liter concentrations. Several injection and preconcentration techniques were evaluated for this purpose, i.e., on-column injection, split/ splitless injection, solid-phase microextraction (SPME), and purge and trap (P&T) in combination with gas chromatography-isotope ratio mass spectrometry. The delta13C values of the target compounds were determined by liquid injections of the analytes dissolved in diethyl ether or, in the case of P&T and SPME, by extraction from water spiked with the analytes. P&T extraction was the most efficient preconcentration technique reaching method detection limits (MDLs) from 0.25 to 5.0 microg/L. These are the lowest MDLs reported so far for continuous-flow isotope ratio determinations, using a commercially available and fully automated system. Isotopic fractionation resulting from preconcentration and injection was investigated and quantified for the priority groundwater pollutants methyl tert-butyl ether (MTBE), chloroform, tetrachloromethane, chlorinated ethylenes, benzene, and toluene. The isotopic fractionations caused by the extraction techniques were small but highly reproducible and could therefore be corrected for. P&T was characterized by a higher reproducibility and smaller isotopic fractionations than SPME. Among the liquid injection techniques, cold on-column injection resulted in slightly better precision compared to split/splitless injection. However, the MDLs determined for liquid injections were 4-6 orders of magnitude higher (i.e., 9.5-2800 mg/L) than for P&T and SPME. Since both of the latter methods are solventless, a better chromatographic resolution was obtained than for the liquid injection techniques. The P&T and SPME methods described here are also applicable for CSIA of D/H ratios, which require 10-20 times higher analyte concentrations than 13C/12C analysis. Finally, the applicability of the described methods is demonstrated for pollutant concentrations of only 5-60 microg/L in environmental samples.
Wines from three important wine-producing regions, Stellenbosch, Robertson, and Swartland, in the Western Cape Province of South Africa, were analyzed by ICP-MS and the elemental composition used in multivariate statistical analysis to classify the wines according to geographical origin. The method is based on the assumption that the provenance soil is an important contributor to the trace element composition of a wine. A total of 40 elements were determined in 40 wines. Of these, 20 elements: Li, B, Mg, Al, Si, Cl, Sc, Mn, Ni, Ga, Se, Rb, Sr, Nb, Cs, Ba, La, W, Tl, and U showed differences in their means across the three areas. In a stepwise discriminant analysis procedure, functions based on linear combinations of the log-transformed element concentrations of Al, Mn, Rb, Ba, W, and Tl were generated to correctly classify wines from each region. In an alternative approach, a pairwise discriminant analysis procedure, not previously used in wine provenance studies, was tested. In this procedure, the classification was done in three steps, with each step classifying a wine as coming from a certain region or not. The combination of elements characterizing wines from a particular region was different in each region. The discriminant functions were based on the following elements: Al, Mn, Rb, Ba, and W for Stellenbosch; Se, Rb, Cs, and Tl for Robertson; and Al, Mn, Rb, Sr, Ba, and Tl for Swartland. After this procedure, the classification of the wines into one of the groups was 100% successful.
C scale.Four laboratories (Centrum voor Isotopen Onderzoek,Groningen, The Netherlands; Max-Planck-Institute forBiogeochemistry, Jena, Germany; UFZ Leipzig-Halle, Leipzig,Germany; US Geological Survey, Reston, VA, USA) per-formed analytical measurements. Participants at the USNational Institute of Science and Technology (NIST) headedthe task to estimate consensus means and uncertainties usingmultivariate Bayesian techniques. Collectively, the labora-tories performed 1055 state-of-the-art continuous-flowelemental-analyzer mass spectrometry measurements usingthe general method of Qi et al.
Template DNAs were extracted from wine and purified for use as samples for PCR to differentiate grape cultivars. It has been pointed out that the authentication of grape material by PCR using wine as a material is very difficult. The problems are (1) decomposition of DNAs during fermentation; (2) contamination of DNAs from microorganisms such as yeast; (3) interference of DNA extraction by polysaccharides and polypeptides in the beverages; and (4) coexistence of PCR inhibitors, such as polyphenols. For this study was developed a novel preparation method of template DNA from wine to differentiate grape cultivars using PCR by (1) lyophilizing and pulverizing the fermented beverage to concentrate the DNAs; (2) decomposition of polysaccharides and proteins so as not to inhibit DNA extraction using heat-resistant amylase and proteinase K without DNA damage by endogenous DNase; and (3) separation of the template DNAs for PCR from PCR inhibitors, such as polyphenols, by purification using 70% EtOH extraction and isopropyl alcohol precipitation. To prevent the amplification of microorganisms' DNAs during PCR, suitable PCR primers closely related to the specific plant DNAs, such as chloroplast DNA and mitochondrial DNA, were selected. The sequences of the amplified DNAs by PCR were ascertained to be the same as those of grape materials.
the predominant raw material of vinegar F was an apple juice, the δ LITERATURE CITED (1) Anderson, K. A.; Smith, B. W. Chemical profiling to differentiate geographic growing origins of coffee
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If, for example, the predominant raw material of vinegar F was an apple juice, the δ LITERATURE CITED (1) Anderson, K. A.; Smith, B. W. Chemical profiling to differentiate geographic growing origins of coffee. J. Agric. Food Chem. 2002, 50, 2068.
Determining the geographical origin of milk in Australasia using multi-element stable isotope ratio analysis) F€ orstel, H. The natural fingerprint of stable isotopes-use of IRMS to test food authenticity
- R Stockmann
Stockmann, R. Determining the geographical origin of milk in Australasia using multi-element stable isotope ratio analysis. Int. Dairy J. 2007, 17, 421. (8) F€ orstel, H. The natural fingerprint of stable isotopes-use of IRMS to test food authenticity. Anal. Bioanal. Chem. 2007, 388, 541.
Hattori et al. plants (which vary from about -22 to -35%) are lower than those of C 4 plants (which vary from about -8 to -20%)
- However
However, when the extraction time exceeded 20 min, the δ 7118 J. Agric. Food Chem., Vol. 58, No. 12, 2010 Hattori et al. plants (which vary from about -22 to -35%) are lower than those of C 4 plants (which vary from about -8 to -20%) (19, 20).
Deuterium transfer in the bioconversion of glucose to ethanol studies by specific isotope labeling at the natural abundance level Received for review
- M L Martin
Martin, M. L. Deuterium transfer in the bioconversion of glucose to ethanol studies by specific isotope labeling at the natural abundance level. J. Am. Chem. Soc. 1986, 108, 5116. Received for review February 1, 2010. Revised manuscript received May 14, 2010. Accepted May 20, 2010.
carbon and nitrogen isotopic analysis of natural and synthetic caffeines. Authen-tication of coffees and coffee extracts Authentication of natural vanilla flavorings: Isotopic characterization using degrada-tion of vanillin into guaiacol
- D Danho
- N Naulet
- G J Martin
- Deuterium
- F F Bensaid
- K Wietzerbin
- G J Martin
- H W Krueger
Danho, D.; Naulet, N.; Martin, G. J. Deuterium, carbon and nitrogen isotopic analysis of natural and synthetic caffeines. Authen-tication of coffees and coffee extracts. Analysis 1992, 20, 179. (10) Bensaid, F. F.; Wietzerbin, K.; Martin, G. J. Authentication of natural vanilla flavorings: Isotopic characterization using degrada-tion of vanillin into guaiacol. J. Agric. Food Chem. 2002, 50, 6271. (11) Krueger, H. W.;