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Analysis of beverages by capillary electrophoresis

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Abstract

Rapid analysis of carbonated beverages by capillary electrophoresis (CE) allows the simultaneous determination of aspartame, benzoic acid and caffeine in 2 min using 20 mM glycine buffer at pH 9.0 and direct detection at 215 nm. The rapid determination of these compounds with minimal sample preparation offers an excellent method for evaluating stability and shelf-life of commercial products. This method is easily adapted to the analysis of these substances in other aqueous-based consumer products.

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... Surveys on the presence of benzoic acid in soft drinks in two different studies, conducted by Walker, Zaugg, and Walker (1997) and Tyler (1984), in USA, revealed that the ranges found were higher than those reported in the present study. However, those found in Spain are similar (Suárez, Masferrer, Vázquez, & Centrich, 1997). ...
... The results found for saccharin in the present study are similar to those found in Spain by Suárez et al. (1997), lower than those found in USA by Tyler (1984), and higher than those observed in Denmark (Leth et al., 2007). The levels found for caffeine in USA (Tyler, 1984;Walker et al., 1997) and in Spain (Suárez et al., 1997) are higher. The caffeine concentrations found in diet cola drinks analysed between 1995 and 2004, in Portugal, ranged from 81.5 to 124 mg/L, reflecting the differences observed in caffeine content for different brands (Pena et al., 2005) (Table 4). ...
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A reliable method for the determination of benzoic and sorbic acids, caffeine and saccharin in soft drink and nectars using high performance liquid chromatography and UV detection was validated. The chromatographic separation was achieved with a C18 column (250 × 4.6 mm) and one buffered mobile phase, KH2PO4 0.02 M/ACN (90:10)/phosphoric acid at pH 4.2. The effluent was monitored at 220 nm.Benzoic acid was detected in 19 soft drinks, being 11 traditional soft drinks and 8 based on mineral water, with mean concentrations of 158 and 148 mg/L, respectively. Fifteen samples, 7 traditional and 8 based on mineral water, contained sorbic acid, with mean concentrations of 172 and 188 mg/L, respectively.Saccharin and caffeine were not detected in soft drinks based on mineral waters. In contrast, 6 samples of traditional drinks contained both additives, with mean levels of 75 and 97 mg/L, respectively. The four additives were not detected in nectar samples.According to European Union and Portuguese legislation, the maximum permitted level (MPL) for benzoic acid was exceeded in 10 soft drinks, and the MPL for sorbic acid overlapped in 3 samples of the referred samples. Two samples exceeded the MPL for the sum of both preservatives, and in 1 sample the MPL for saccharin was overlapped.The estimated daily intakes (EDI) of benzoic, sorbic acid, and saccharin for the average consumer were below the acceptable daily intakes (ADIs). For benzoic acid, the EDIs were 0.25 and 0.32 mg/kg b.w./day, representing 4.9%, and 6.4% of the ADI, respectively for traditional soft drinks and soft drinks based on mineral water. A similar situation was observed for sorbic acid. In this way, the EDIs were 0.17 and 0.41 mg/kg b.w./day, representing only 0.68% and 1.6% of the ADI for the same kind of drinks. For saccharin, the EDI represents 1.28% of the ADI. The EDI for caffeine was 0.08 mg/kg b.w./day.
... A previous study in Portugal on the presence of BA and SA in soft drinks, performed by Lino and Pena (2010), showed a similar high number of positive samples for both preservatives with similar concentration ranges and mean concentrations. Survey on presence of BA in soft drinks in USA, conducted by Walker et al. (1997), revealed that the range found was higher than those reported in the present study. However, studies in Spain (Suárez et al., 1997), and China 288.9 ± 98.6 2 a Only one sample presented BA + SA with 224.5 mg/L. ...
... In this study, caffeine occurred in a larger number of samples, when compared with the results reported by Lino and Pena (2010), but in similar concentrations. The levels for caffeine in USA (Walker et al., 1997) and in Spain (Suárez et al., 1997) are higher. ...
... Similar situation is in other countries around the world, where the main dietary source of benzoic (11). The analytical results of the current study showed that mean levels of benzoic acid in non alcoholic beverages were lower than those found in most of other studies from Portugal (12), Brazil (13), Belgium (14), United Kingdom (15) and USA (16). In the study from Korea (17) benzoic acid was not detected in carbonated beverages and in our study in some samples of cola beverages. ...
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The aim of this study is to estimate dietary intake of benzoic acid and its salts through food additives in adult population of South East Serbia. Information on dietary intake among 620 adults (aged 18-65) was collected using a food frequency questionnaire, and 748 food samples were analyzed. The mean estimated intake of benzoic acid -0.32 mg/kg of body weight (bw) per day was below acceptable daily intake (ADI). Dietary exposure to benzoic acid (0.36 mg/kg of bw/day; 7.2% ADI) (consumer only), also did not exceed ADI. The main contributors of benzoic acid to dietary intake were non alcoholic beverages (43.1%), ketchup and tomato products (36.1%), and domestic pickled vegetables (19.4%). The results of this study indicate that dietary exposure to benzoic acid and its salts through food preservatives does not represent a public health risk for the adult population of South East Serbia.
... Despite these restrictions, the growing use of aspartame in the food industry warrants a simple, reliable, and rapid method for its determination. Various methods such as capillary electrophoresis (Pesek and Matyska 1997;Walker et al. 1997), spectrophotometry (Vesely et al. 1980;Prasad et al. 1988;Fatibello-Filho et al. 1999), and high-performance liquid chromatography (HPLC) Gibbs et al. 1996;Demiralay et al. 2006) were proposed for the determination of aspartame. In recent years the use of high-performance liquid chromatography (HPLC) has become the method of choice for aspartame analysis because it is relatively simple while providing generally good qualitative and quantitative R. A. Medeiros et al. 3196 results for many types of samples. ...
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The use of square‐wave voltammetry in conjunction with a cathodically pretreated boron‐doped diamond electrode for the analytical determination of aspartame in dietary products is described. In this determination, the samples were analyzed without previous treatment in a 0.5 mol l H2SO4 solution. A single oxidation peak at a potential of 1.6 V vs. Ag/AgCl (3.0 mol l KCl) with the characteristics of an irreversible reaction was obtained. The analytical curve was linear in the aspartame concentration range 9.9×10 to 5.2×10 mol l with a detection limit of 2.3×10 mol l. The relative standard deviation (n=5) obtained was smaller than 0.2% for the 1.0×10 mol l aspartame solution. The proposed method was applied with success to the determination of aspartame in several dietary products and the results were similar to those obtained using an HPLC method at 95% confidence level.
... Caffeine has been determined in drinks by different analytical techniques, such as UV-vis spectrophotometry [2], potentiometry [3] or amperometry [4] and most frequently by using separation methods like liquid chromatography (LC) [5], ion chromatography [6], high performance thin layer chromatography (HPTLC) [7], capillary electrophoresis [8], micellar capillary electrophoresis [9] as well as gas chromatography [10] and solid-phase microextraction gas chromatography [11]. ...
Article
A solid-phase vibrational spectrometry-based methodology (solid-phase Fourier transform-Raman spectrometry, SP-FT-Raman) has been developed for caffeine determination in commercial energy drink samples. The Raman spectra of caffeine, fixed on a C18 solid phase packed into a glass tube of 5 mm i.d., was obtained directly between 3500 and 70 cm−1. In order to quantify caffeine, Raman intensity between 573 and 542 cm−1 corrected using a baseline defined between 580 and 540 cm−1 was used. A repeatability of 3%, as relative standard deviation of five analysis of a 200 mg l−1 concentration, and a limit of detection of 18 mg l−1 were obtained. The SP-FT-Raman procedure provides a sampling frequency of 13.3 h−1, higher than that of liquid chromatography (LC), which was 7.0 h−1. The use of FT-Raman reduces the reagent consumption and waste generation, also minimizing the sample handling. Results obtained by the developed procedure were statistically comparable with those found by a reference LC method.
... According to previous investigations, the analysis of carbonated beverages by capillary electrophoresis (CE) enabled the simultaneous determination of aspartame, benzoic acid, and caffeine in 2 min with minimal sample preparation. 24 The LODs for caffeine, aspartame, and benzoic acid were 1.6, 18, and 4.0 mg/L, respectively. Another study compared UV spectrophotometry, liquid chromatography (LC), and CE for the quantification of caffeine, aspartame, and benzoic acid in soft drinks. ...
Article
¹H Nuclear magnetic resonance (NMR) spectroscopy (400 MHz) was used in the context of food surveillance to develop a reliable analytical tool to differentiate brands of cola beverages and to quantify selected constituents of the soft drinks. The preparation of the samples required only degassing and addition of 0.1% of TSP in D₂O for locking and referencing followed by adjustment of pH to 4.5. The NMR spectra obtained can be considered as "fingerprints" and were analyzed by principal component analysis (PCA). Clusters from colas of the same brand were observed, and significant differences between premium and discount brands were found. The quantification of caffeine, acesulfame-K, aspartame, cyclamate, benzoate, hydroxymethylfurfural (HMF), sulfite ammonia caramel (E 150D), and vanillin was simultaneously possible using external calibration curves and applying TSP as internal standard. Limits of detection for caffeine, aspartame, acesulfame-K, and benzoate were 1.7, 3.5, 0.8, and 1.0 mg/L, respectively. Hence, NMR spectroscopy combined with chemometrics is an efficient tool for simultaneous identification of soft drinks and quantification of selected constituents.
... At present, the most promising methods seem to be those based on separation approaches such as capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). Thus, the separation of some additives by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) has been described in several papers [15][16][17][18][19][20][21][22][23][24], but these techniques are affected by sensitivity problems as a result of small injection volumes. Similarly, several reversed-phase, ion-pair and anion-exchange HPLC methods have been developed [25][26][27][28][29][30], even though almost all of these methods are affected by some drawbacks, in that they enable the determination of only specific classes of additives and require frequently a lengthy extractive pre-treatment of the sample, usually with incomplete recovery of some of the searched species. ...
Article
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A reverse-phase HPLC method for the simultaneous determination of the main artificial sweeteners, preservatives and dyes present in soft drinks is proposed. It involves the use of a 10 μm LiChrosorb RP18 column and a binary eluent consisting of aqueous 0.1 M phosphate buffer (pH 4.0) added with methanol, according to a suitable gradient elution program. Good separations were obtained within less than 20-min run-time, with a satisfactory precision. The sensitivity of spectrophotometric detection was optimised by adopting a wavelength switching technique, thus achieving for all the additives considered detection limits ranging from 0.1 to 3.0 mg L−1, well below the maximum permitted levels. The method was applied to some commercial soft drinks, whose analysis required minimum pre-treatment before direct injection.
... Aspartame was analyzed by using thin layer chromatography (TLC) using ninhydrin as a visualization reagent [6]. Several capillary electrophoresis (CE) methods were reported for analysis of aspartame with UV detection at 254 nm [7][8][9]. Flow injection analysis (FIA) of aspartame was performed using ninhydrin as colorimetric reagent [10]. A bienzymatic electrode has been utilized for electrochemical analysis of aspartame [11]. ...
Article
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A new, simple normal phase high performance liquid chromatographic method was developed for the analysis of aspartame in tabletop sweeteners. The method is based on the derivatization of aspartame with 2, 4-dinitrofluorobenzene followed by detection at 332 nm. Separation was carried on silica column with hexane: ethyl acetate (60: 40, V/V) as mobile phase (pH was adjusted to 4.5 using 1% acetic acid) with a flow rate of 1 ml/min. The limit of detection (LOD) and limit of quantification (LOQ) of this method was found to be 1 ng and 4 ng respectively. The method was found to be linear in the concentration range of 20-180 ng. The recovery values of this method were found to be better than 97%.
... Analytical methods used for determination of benzoic acid include spectroscopic technique [11,12], gas chromatography (GC) [13,14], high performance liquid chromatography (HPLC) [15,16] or capillary electrophoresis [17]. All of them involve extensive extraction procedures which are timeconsuming and expensive. ...
Article
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Diureidocalix[4]arene have been applied as new ionophore in liquid membraneelectrode (ISE) sensitive towards un-dissociated benzoic acid. The electrode demonstratedresponse towards benzoic acid with the detection limit 2.0 x 10-4 M which is sufficient forthe determination of benzoic acid added to beverages as preservative in milimolarconcentration. The selectivity coefficients measured by the matched potential method(MPM) showed its good selectivity against common anions present in drink samples. Allmeasurements were made in presence of 1.0 x 10-2 M NaHSO4 pH 3.0 in order to reducethe influence of OH-. The applicability of diureidocalix[4]arene incorporated ISE has beenchecked by recovery test of benzoic acid in the presence of artificial drink matrix and bystandard addition method.
... Because of the importance of this anion, its detection has become an essential issue. Despite the availability of certain analytical methods based on chromatography [14,15] or capillary electrophoresis [16], it would be desirable to obtain synthetic receptors which could be applied to the sensing of benzoate by simple molecular recognition processes. ...
Article
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The indolo[2,3-a]carbazole scaffold is a fused polyheteroaromatic system bearing two NH groups which suitably converge as hydrogen bond donor sites for the recognition of anions. A simple derivatisation of the indolocarbazole system at positions 1 and 10 with different functional groups, namely alcohols and amides, has contributed to modulate the anion binding selectivity and sensibility. A particularly good response has been obtained for the benzoate anion.
... The major disadvantages are the high cost of both the basic equipment and its subsequent maintenance services. These limitations also apply to GLC, particularly when attached to mass spectrometry, as well as to capillary electrophoresis [37]. ...
Article
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The characteristics, performance, and application of an electrode, namely, Pt | Hg | Hg2(Bzt)2 | graphite, where Bzt stands for benzoate ion, are described. This electrode responds to Bzt with sensitivity of 57.7±1.0 mV/decade over the range 5×10−4–1×10−1 mol l−1 at pH 6.0–8.0 with a detection limit of 1.6×10−4 mol l−1. The electrode shows easy construction, fast response time (between 10–30 s), low-cost, and excellent response stability (lifetime>6 months, in continuous use). The proposed sensor displayed good selectivity for benzoate in the presence of several carboxylate and inorganic anions. It was used to determine benzoate in various beverages by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by the official AOAC spectrophotometric method and by a HPLC procedure as well.
... This method was tested to determine nanomolar concentration levels of sorbic and benzoic acids. These acids are common food additives where the preconcentration step prior to capillary zone electrophoresis is necessary for their determination [41][42][43][44][45][46][47][48]. A comparison of the proposed method with ITP/CZE and ITP/ITP is included. ...
Article
An on-line preconcentration capillary electrophoresis (CE) technique, which combines a large volume sample stacking with a dynamic pH junction technique, is introduced in this paper. This dynamic pH junction with co-electroosmotic migration is formed between sodium borate pH 9.5 and sodium phosphate pH 2.5 with 150 mM sodium dodecylsulfate (SDS). A full capillary based injection allows determination of weak acidic compounds at ppb concentration levels (achieved LOD for benzoic acid was 11 nmol L(-1)). The proposed preconcentration method was compared with ITP/ITP (LOD 120 nmol L(-1)), ITP/CZE (LOD 740 nmol L(-1)) and a simple CZE method (LOD 23,330 nmol L(-1)). The analytical potential of this method was assessed with juice test samples.
... Usando electroforesis capilar Walker et al. 24 , realizaron análisis en bebidas de cola, obteniendo cantidades superiores en la Coca-Cola light e inferiores en la Pepsi-cola normal (Tabla III). ...
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Introduction: soft drinks are becoming increasingly consumed by society. They are composed by a great variety of components, some of which can produce adverse effects if they are frequently consumed in high levels. Objectives: determine caffeine and quinine concentration to prove that those concentration levels are lower than the legal limits allowed and calculate the contribution to dietary intake to obtain the Estimated Daily Intake. Methods: levels of caffeine and quinine of the main brands of soft drinks were analyzed using High-Performance Liquid Chromatography technique. Results: concentrations were obtained for all brands, and the medium level was estimated. Conclusions: it has been observed that in any case the maximum concentration limits are exceeded and the contribution to dietary intake doesn't mean adverse reaction.
... To give an example, methods available for SAC in foodstuffs include spectrometry [7], differential pulse polarography [8], sublimation [9], potentiometry [10][11][12], micellar electrokinetic capillary chromatography [13] and high performance liquid chromatography (HPLC) [14][15][16][17]. Several papers have demonstrated the utility of capillary electrophoresis for the analysis of various artificial sweeteners [18][19][20]. As spectrophotometric, gravimetric or electrochemical methods are very often too time consuming, HPLC in combination with ultraviolet (UV) detection has very often become the method of choice for the determination of individual artificial sweeteners such as SAC, ASP, ACS and NHDC [21]. ...
Article
A high performance liquid chromatographic method with evaporative light scattering detection (HPLC-ELSD) has been developed for the simultaneous determination of multiple sweeteners, i.e., acesulfame-K, alitame, aspartame, cyclamic acid, dulcin, neotame, neohesperidine dihydrochalcone, saccharin and sucralose in carbonated and non-carbonated soft drinks, canned or bottled fruits and yoghurt. The procedure involves an extraction of the nine sweeteners with a buffer solution, sample clean-up using solid-phase extraction cartridges followed by an HPLC-ELSD analysis. The trueness of the method was satisfactory with recoveries ranging from 93 to 109% for concentration levels around the maximum usable dosages for authorised sweeteners and from 100 to 112% for unauthorised compounds at concentration levels close to the limit of quantification (LOQs). Precision measures showed mean repeatability values of <4% (expressed as relative standard deviation) for highly concentrated samples and <5% at concentration levels close to the LOQs. Intermediate precision was in most cases <8%. The limits of detection (LODs) were below 15 microg g(-1) and the LOQs below 30 microg g(-1) in all three matrices. Only dulcin showed slightly higher values, i.e., LODs around 30 microg g(-1) and LOQs around 50 microg g(-1)
... In the USA, the same sweetener was found by Tyler (1984) in two diet cola drinks at levels of 97 and 92 mg ml À1 . Also, Walker et al. (1997) detected aspartame in two soft drinks, one of diet cola with 206 mg and another of diet lemon carbonated soft drink with 185 mg, by a scan of 355 ml, corresponding to 580 and 521 mg l À1 , respectively. In China, Zhu et al. (2005) found levels of 7234.6 and 2826.3 mg l À1 in two samples of cola soft drinks. ...
Article
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In a survey of levels of acesulfame-K and aspartame in soft drinks and in light nectars, the intake of these intense sweeteners was estimated for a group of teenage students. Acesulfame-K was detected in 72% of the soft drinks, with a mean concentration of 72 mg l(-1) and aspartame was found in 92% of the samples with a mean concentration of 89 mg l(-1). When data on the content of these sweeteners in soft drinks were analysed according to flavour, cola drinks had the highest mean levels for both sweeteners with 98 and 103 mg l(-1) for acesulfame-K and aspartame, respectively. For soft drinks based on mineral water, aspartame was found in 62% of the samples, with a mean concentration of 82 mg l(-1) and acesulfame-K was found in 77%, with a mean level of 48 mg l(-1). All samples of nectars contained acesulfame-K, with a mean concentration of 128 mg l(-1) and aspartame was detected in 80% of the samples with a mean concentration of 73 mg l(-1). A frequency questionnaire, designed to identify adolescents having high consumption of these drinks, was completed by a randomly selected sample of teenagers (n = 65) living in the city of Coimbra, in 2007. The estimated daily intakes (EDI) of acesulfame-K and aspartame for the average consumer were below the acceptable daily intakes (ADIs). For acesulfame-K, the EDI was 0.7 mg kg(-1) bw day(-1) for soft drinks, 0.2 mg kg(-1) bw day(-1) for soft drinks based on mineral waters, and 0.5 mg kg(-1) bw day(-1) for nectars, representing 8.0%, 2.2%, and 5.8% of the ADI, respectively. A similar situation was observed for aspartame. In this way, the EDI for soft drinks was 1.1 mg kg(-1) day(-1), representing only 2.9% of the ADI. In respect of nectars, the EDI was 0.2 mg kg(-1) bw day(-1), representing 0.5% of the ADI. Soft drinks based on mineral waters showed the lowest EDI values of 0.3 mg kg(-1) bw day(-1), accounting for 0.7% of the ADI.
Article
Capillary electrophoresis (CE) offers the possibility of fast, cheap and reproducible separations for pharmaceutical preparations. Alkylxanthines make up a family of compounds that are used in the treatment and prevention of bronchi asthma and chronic pulmonary disease. The group of analysed compounds include caffeine, dyphylline, theophylline, theobromine and enprofylline. This paper shows a simple capillary zone electrophoretic (CZE) method for separation of this group of xanthines. Using 20 mM borate buffer at pH 9.4 as running buffer at 55 °C it was possible to complete a total separation of a sample in 2 min. Limits of detection in the range 1.9–2.5 mg l−1 were achieved with %R.S.D. of 0.06–0.22% (n = 5). The technique is applied to a range of samples containing the analytes, including tablets and chocolate. Reproducibility (%R.S.D.) of the chocolate analysis technique by CZE was less than 4.5%.
Article
A novel quantitative approach for the determination of sodium benzoate (SB) was proposed by the kinetic study about its competitive inhibitory efficiency to D-amino acid oxidase (DAAO) activity with a chiral ligand exchange capillary electrophoresis (CE) method, in which the Zn(II)-L-prolinamide complex was chosen as a novel chiral selector. After the optimization of buffer pH and the chiral selector concentration this chiral ligand exchange CE method was employed to determine labeled D,L-Serine with good linearity (r(2)≥0.995), efficient recovery (95.6-100.9%) and remarkable reproducibility (RSD≤1.2%). This chiral separation method was further used to observe DAAO activity through the determination of D-Serine concentration variation after being incubated with DAAO and obtain the sigmoidal inhibitory curve of SB to DAAO activity. The ascending part of this inhibitory curve was linearly fitted in a limited range for SB from 2.0 to 200 μM with an appropriate coefficient of determination (R(2)=0.990). The linearity was then validated to be a promising method for the analysis of SB with the standout merits of high selectivity and adjustable detection range. Furthermore, this proposed method was used for the pharmacokinetics study of SB.
Chapter
Introduction to sweeteners Properties of sweeteners Intense sweeteners in foods Bulk food sweeteners Quality assurance and quality control Analytical methods References Further reading
Article
An interlaboratory trial was conducted to validate an analytical method based on high-performance liquid chromatographic analysis with evaporative light-scattering detection for the simultaneous determination of 9 intense sweeteners, i.e., acesulfame-K, alitame, aspartame, cyclamic acid, dulcin, neotame, neohesperidine dihydrochalcone, saccharin, and sucralose in carbonated and noncarbonated soft drinks and canned or bottled fruits. Seven laboratories participated in the validation study. The majority of the samples fortified with levels close to the limit of quantification had relative standard deviation for reproducibility (RSDR) values <15%. In most cases, the recovery rates ranged between 90 and 105%, demonstrating satisfactory performance of the method. For samples fortified at levels comparable to the prescribed legal limits stipulated in the current European Union legislation, the method produces acceptably accurate, repeatable, and reproducible results. Trueness, expressed in terms of recovery rates, was demonstrated in most cases by values ranging from 90 to 108%. Comparability of results obtained by individual testing laboratories was good (RSDR values <10%) for the majority of results. Moreover, HorRat values of <1.1 suggested good performance of the method for all sweeteners and matrixes tested.
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This review deals with the determination of impurities in pharmaceuticals by electromigration methods in the capillary format. These separation methods are either based on the different effective mobility of the charged analytes (as in zone electrophoresis and isotachophoresis) or include hybrid methods such as micellar electrokinetic chromatography, microemulsion electrokinetic chromatography and electrochromatography. The pharmaceutically active compounds under consideration belong to chemotherapeutic agents, central nervous system drugs, histamine receptor drugs, cardiovascular drugs, anticancer drugs, anti-inflammatory drugs and some other drugs. The review discusses about 150 publications from the period between 1980 and 2007 with special emphasis on the recent trends and gives details about the experimental conditions applied for analyses and the obtained analytical performance parameters.
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A capillary electrophoretic method, for the determination of antioxidants present in food, has been developed using mixed micellar electrokinetic capillary chromatography. The buffer consists of sodium cholate (40 mM), sodium dodecyl sulfate (15 mM), 10% methanol, and 10 mM borate at pH 9.3. A separation was obtained for nine antioxidants (synthetic and natural) commonly found in food. High-performance liquid chromatography and capillary electrophoresis were applied to the analysis of sesame oil and wine. Ascorbic acid was identified in wine.
Article
Capillary electrophoresis (CE) offers the analyst a number of key advantages for the analysis of the components of foods. CE offers better resolution than, say, high-performance liquid chromatography (HPLC), and is more adept at the simultaneous separation of a number of components of different chemistries within a single matrix. In addition, CE requires less rigorous sample cleanup procedures than HPLC, while offering the same degree of automation. However, despite these advantages, CE remains under-utilized by food analysts. Therefore, this review consolidates and discusses the currently reported applications of CE that are relevant to the analysis of foods. Some discussion is also devoted to the development of these reported methods and to the advantages/disadvantages compared with the more usual methods for each particular analysis. It is the aim of this review to give practicing food analysts an overview of the current scope of CE.
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A review of the applications of electrophoresis to the determination of various compounds in beverage samples, namely beer, hard drinks, juice, milk, soft drinks, tea and wine, is presented.
Article
The application of capillary electrophoresis (CE) to the analysis of additives in food has been reviewed. Additives included in the review are preservatives, antioxidants, sweeteners, colourings, caffeine, niacin, choline, nitrate, and nitrite. The review highlights the versatility of CE in separating this often widely disparate group of compounds. The application of the methods to real food samples is also discussed.
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In this study the use of a single continuous-flow solid-phase UV spectrophotometric sensing system for determination of methylxanthines was evaluated. Two methods were developed to determine caffeine (CF) and theophylline (TP) in pharmaceuticals and CF and theobromine (TB) in food and beverages. The sensor is based on transient and sequential retention of the analytes on a hydrophobic sensing solid zone (octadecyl silane C18 gel) and detection of their intrinsic UV absorbance. Temporary sequencing of the arrival of the analytes at the sensing zone is achieved by on-line separation of one of the analytes using a pre-column of the same particulate material, placed just before the flow cell. After TB or TP had been carried toward the sensing zone (by the appropriate carrier solution), produced its transitory signal, and been eluted by the carrier, an appropriate eluting solution (25% MeOH) was used to elute CF, which was strongly retained on the minicolumn, so that its transient signal could be recorded. The sensing zone was completely regenerated with this eluting solution, and so was ready for analysis of another sample. After selecting the most suitable conditions, the sensing system was calibrated in the range 1-16 and 1-12 mg L(-1) for CF and TP-TB, respectively, giving detection limits below 0.1 mg L(-1) with RSD values less than 3%. The usefulness of this approach has been evaluated by applying it to the determination of caffeine, theobromine, and theophylline in different samples of food, beverages, and pharmaceutical formulations. The results were in satisfactory agreement with those obtained by use of an HPLC reference method.
Article
A simple, quick and organic solvent saving procedure has been developed for the GC/MS determination of caffeine in beverages. The procedure involves the mixing of 25 microL sample with 1 mL ethyl acetate, and a following simple desiccation procedure in a 1.5 mL autosampler vial. A linear calibration curve was generated with caffeine concentration ranging from 0.005 mg/L to 30.0mg/L. The procedure developed provides a 0.001 mg/L detection limit of caffeine in the final solution by injection of 1 microL solution and the relative standard deviation (RSD) was less than 2% for independent measurement. The total amount of organic solvent used for individual detection is 1 mL of nontoxic ethyl acetate. The developed method was repeatable and could be applied to determine trace amounts of caffeine in popular commercial beverages.
Article
The aim of this study was to develop a fast capillary electrophoresis method for the determination of benzoate and sorbate ions in commercial beverages. In the method development the pH and constituents of the background electrolyte were selected using the effective mobility versus pH curves. As the high resolution obtained experimentally for sorbate and benzoate in the studies presented in the literature is not in agreement with that expected from the ionic mobility values published, a procedure to determine these values was carried out. The salicylate ion was used as the internal standard. The background electrolyte was composed of 25 mmol L(-1) tris(hydroxymethyl)aminomethane and 12.5 mmol L(-1) 2-hydroxyisobutyric acid, at pH 8.1. Separation was conducted in a fused-silica capillary (32 cm total length and 8.5 cm effective length, 50 microm I.D.), with short-end injection configuration and direct UV detection at 200 nm for benzoate and salicylate and 254 nm for sorbate ions. The run time was only 28s. A few figures of merit of the proposed method include: good linearity (R(2)>0.999), limit of detection of 0.9 and 0.3 mg L(-1) for benzoate and sorbate, respectively, inter-day precision better than 2.7% (n=9) and recovery in the range 97.9-105%. Beverage samples were prepared by simple dilution with deionized water (1:11, v/v). Concentrations in the range of 197-401 mg L(-1) for benzoate and 28-144 mg L(-1) for sorbate were found in soft drinks and tea.
Article
Capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D) was used for simple, rapid, and simultaneous determination of aspartame, cyclamate, saccharin and acesulfame-K in commercial samples of soft drinks and tabletop sweetener formulations. A buffer solution containing 100 mmol L−1 tris(hydroxymethyl)aminomethane (TRIS) and 10 mmol L−1 histidine (His) was used as background electrolyte (BGE). A complete separation of the analytes could be attained in less than 6 min. The limits of detection (LOD) and quantification (LOQ) were considered better than those usually obtained by CE with photometric detection. Recoveries ranging from 94% to 108% were obtained for samples spiked with standard solutions of the sweeteners. The relative standard deviation (RSD) for the analysis of the samples with the CE-C4D method varied in the range of 1.5%–6.5%.
Article
A rapid capillary electrophoresis method was developed simultaneously to determine artificial sweeteners, preservatives and colours used as additives in carbonated soft drinks. Resolution between all additives occurring together in soft drinks was successfully achieved within a 15-min run-time by employing the micellar electrokinetic chromatography mode with a 20 mM carbonate buffer at pH 9.5 as the aqueous phase and 62 mM sodium dodecyl sulfate as the micellar phase. By using a diode-array detector to monitor the UV–visible range (190–600 nm), the identity of sample components, suggested by migration time, could be confirmed by spectral matching relative to standards.
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Caffeine and vitamins C, PP, and B6 have been determined in energy drinks by capillary electrophoresis. Its advantages and disadvantages over high-performance liquid chromatography have been considered and the influence of analysis conditions on the error of analysis and error sources in capillary electrophoresis have been estimated.
Article
A new, simple normal phase high performance liquid chromatographic method was developed for the analysis of aspartame in tabletop sweeteners. The method is based on the derivatization of aspartame with 2, 4-dinitrofluorobenzene followed by detection at 332 nm. Separation was carried on silica column with hexane: ethyl acetate (60: 40, V/V) as mobile phase (pH was adjusted to 4.5 using 1% acetic acid) with a flow rate of 1 ml/min. The limit of detection (LOD) and limit of quantification (LOQ) of this method was found to be 1 ng and 4 ng respectively. The method was found to be linear in the concentration range of 20-180 ng. The recovery values of this method were found to be better than 97%.
Article
A new chemiluminescence flow system has been developed for sequential determina-tion of benzoic acid based on the reaction of the compound with copper carbonate entrapped in a solid-phase reactor. It was found that the unsaturated complex of Cu(II) and benzoic acid (1:1) has strong catalytic effect on the luminol-H2O2 chemiluminescence reaction. The calibration graph is linear over the range of 0.025 ∼ 60 μg/mL of benzoic acid, with a relative standard deviation of less than 3.0 %, and the detection limit is 0.01μg·mL-1. The proposed method was applied to the determination of benzoic acid content in different pharmaceutical formulations.
Article
A rapid, accurate and organic solvent saving method has been developed for the ultraviolet spectrophotometric (UV) determination of caffeine in beverages. The centrifugal extraction procedure with large phase ratio was applied to sample micropreparation prior to instrumental analysis. The method involves the mixing of 100 μL sample with 2 mL chloroform and a 3-min centrifugal extraction procedure in a centrifugal tube. The clear solution obtained was directly determined by UV detection at wavelength of 278 nm. The manipulation was simple and repeatable, and the relative standard deviation of the method was less than 3 % for the independent measurement. When added different concentration of standard caffeine solution to three brand beverages, the recovery of the caffeine was in the range of 96.6%-106. 1%. A linear calibration curve was obtained with caffeine concentration ranging from 0.50-30 mg/L, giving the correlation coefficient as 0. 9999. The method provides a 0. 001 mg/L detection limit of caffeine. The developed method was applied to determine the caffeine content in commercial beverages with good results.
Article
A specific inhibition of 3′,5′-cyclic phosphodiesterase (CPDE) from bovine heart by methylxanthines was used in combination with a pH electrode to develop a new biosensing method for the detection of caffeine in coffee. The potential response changes of the sensor were proportional to the concentration of caffeine in the range 0–4 mg ml−1. The response time was about 2–4 min. The standard deviation of five measurements of a 0.2 mg ml−1 caffeine solution was ±7.1 µg ml−1. The electrode gave a detection limit of 0.6 mg l−1 caffeine. The concentration of caffeine in espresso coffee was analysed. This model gave excellent correlation between observed and predicted caffeine values. This electrode exhibits advantages such as fast response, short conditioning time and low cost of the instrumentation used. We also expected to be able to perform the detection of caffeine in food and clinical analysis.© 1999 Society of Chemical Industry
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Energy drinks are becoming popular in Brazil and in the world due to their stimulant properties. Caffeine is present in energy drinks with the aim of stimulating the central nervous system and intensifying brain activity. On the other hand, the ingestion of high doses of caffeine can cause undesirable symptoms such as anxiety and tachycardia. Therefore, it is necessary to monitor the caffeine content added to energy drinks to guarantee that the levels in the final product are in accordance with the labeling and within the legislation limits. The goal of this work was to validate a fast, efficient, and low-cost method for the determination of caffeine in energy drinks by micellar electrokinetic chromatography (MEKC). A total of seven brands were analyzed, each in three lots. The electrolyte was prepared with 50mmol.L-1 of sodium dodecyl sulfate (SDS) and 10mmol.L-1 of sodium carbonate (pH11.0). The mean concentration of caffeine ranged from 122.8 to 318.6mg.L-1. None of the brands had caffeine levels above the maximum limit. Considering the interval of confidence (95%), 72% of the samples had less caffeine than the amount informed on the product label.
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In this work, a rapid and simple method using capillary electrophoresis (CE) was developed for the determination of the benzoate, sorbate, methyl and propylparaben in foodstuffs. A running buffer consisting of 20 mmol L-1 (pH = 9.3) tetraborate enabled separation of the analytes in less than 5 min. The detector wavelength was set at 220 nm. The method was successfully applied to the analysis of sodas, sweeteners, sauces and juices. The range of preservatives found were from 478.5-466.6 mg kg-1 for methylparaben , 83.7-231.3 mg kg-1 for sorbate and 336.7-428.3 mg kg-1 for benzoate.
Book
The Chemistry of Food Additives and Preservatives is an up-to-date reference guide on the range of different types of additives (both natural and synthetic) used in the food industry today. It looks at the processes involved in inputting additives and preservatives to foods, and the mechanisms and methods used. The book contains full details about the chemistry of each major class of food additive, showing the reader not just what kind of additives are used and what their functions are, but also how they work and how they can have multiple functionalities. In addition, this book covers numerous new additives currently being introduced, and an explanation of how the quality of these is ascertained and how consumer safety is ensured.
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A two-dimensional capillary isotachophoretic method (cITP-cITP) using electrolyte system consisting of leading electrolytes (LE1): [10 mM HCl + β-alanine (pH 3.9) + 0.1% hydroxyethylcellulose (HEC)] and (LE2): [10 mM HCl + aminocaproic acid (pH 5.00) + 0.1% HEC], and 5 mM caproic acid as terminating electrolyte (TE) was studied. Two methods of detection, conductometric and UV-Vis, were applied to the determination of selected food preservatives and additives. Practical applicability was demonstrated by simultaneous determination of benzoates, sorbates, citrates and orthophosphates in 12 samples of beverages. The proposed method revealed linearity with R 2 between 0.9992 and 0.9999 for the concentration ranges: 10–100 mg/L (orthophosphate and citrate ions), 20–100 mg/L (sorbates) and 40–120 mg/L for benzoates. The detection limits for all studied ions were from 0.85 to 3.1 mg/L whereas the quantification ones were from 2.8 to 10 mg/L. The variation coefficients for five-fold analysis of all ions ranged between 0.4 and 9.1%. Obtained recoveries (from 97 to 104%) confirmed satisfactory accuracy of the proposed cITP-cITP method for the determination of tested food additives.
Article
Artificial high-intensity sweeteners are used increasingly frequently for food production. The food industry tends to highlight beneficial aspects of their use (e.g., tooth friendliness, increasing the quality of life of those suffering from different forms of diabetes and the possibility of weight control without anyone sacrificing their favorite “unhealthy” drinks or snacks). However, some consumers are deeply concerned about the safety of artificial sweeteners and claim that the food industry is replacing natural beet sugar or cane sugar for purely economic reasons.Most of these food additives have a maximum usable dose or a maximum allowable concentration specified for a given type of food. In order to assure consumer safety, it is necessary to control the content of sweeteners in foodstuffs. Analytical methods (including high-performance liquid chromatography, ion chromatography, thin-layer chromatography, gas chromatography, capillary electrophoresis, flow-injection analysis, electroanalysis and spectroscopy) can determine sweeteners individually and simultaneously in mixtures. This review focuses on the application of some popular analytical procedures for determination of artificial sweeteners in food.
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High-pressure liquid chromatography (HPLC) has established itself as a critically important analytical method for many research and commercial laboratories. Employers expect today’s chemistry graduates to have a working knowledge of liquid chromatography techniques including HPLC. In addition to HPLC, it is becoming more important to educate students about newer separation technologies such as ultra-high-pressure liquid chromatography (UHPLC). Unfortunately, these systems cost significantly more than traditional HPLC instruments, preventing their broad utilization in instrumental teaching laboratories. We have developed an ultra-fast isocratic separation method using traditional HPLC instrumentation that separates five compounds in 1 min. When utilized as a teaching activity, this ultra-fast separation allows students to develop an analytical method, generate standard calibration curves, and analyze unknown samples in a single teaching laboratory period. Furthermore, chromatograms obtained with this new method are similar to UHPLC, allowing students to experience separations similar to those obtained on newer UHPLC systems using a traditional HPLC.
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Non-alcoholic beverages, particularly, bottled water and fruit juices (carbonated and non-carbonated) are the most widespread food industries worldwide. The industry objective is to process at the lowest possible cost while maintaining the organoleptic stability and quality of the final product. The latter can be achieved through strict adherence to quality (ISO 9001/2) and safety (HACCP) management systems. The flow diagrams for the production of bottled water, several juices (orange, lemon, apple), carbonated drinks, coffee and tea are shown accompanied with a synoptical implementation of the HACCP system (critical control points, critical limits, preventive and corrective actions).
Article
The common sweeteners aspartame, cyclamate, saccharin and acesulfame K were determined by capillary electrophoresis with contactless conductivity detection. In order to obtain the best compromise between separation efficiency and analysis time hydrodynamic pumping was imposed during the electrophoresis run employing a sequential injection manifold based on a syringe pump. Band broadening was avoided by using capillaries of a narrow 10μm internal diameter. The analyses were carried out in an aqueous running buffer consisting of 150mM 2-(cyclohexylamino)ethanesulfonic acid and 400mM tris(hydroxymethyl)aminomethane at pH 9.1 in order to render all analytes in the fully deprotonated anionic form. The use of surface modification to eliminate or reverse the electroosmotic flow was not necessary due to the superimposed bulk flow. The use of hydrodynamic pumping allowed easy optimization, either for fast separations (80s) or low detection limits (6.5μmolL(-1), 5.0μmolL(-1), 4.0μmolL(-1) and 3.8μmolL(-1) for aspartame, cyclamate, saccharin and acesulfame K respectively, at a separation time of 190s). The conditions for fast separations not only led to higher limits of detection but also to a narrower dynamic range. However, the settings can be changed readily between separations if needed. The four compounds were determined successfully in food samples.
Article
The complex [TpPh,MeNi(Cl)PzPh,MeH] (I) [TpPh,Me=hydrotris(3-phenyl-5-methyl-pyrazol-1-yl)borate; PzPh,MeH=3-phenyl-5-methyl-pyrazole] has been synthesized and explored as ionophore for the preparation of a poly(vinyl chloride) (PVC) membrane sensor for benzoate anions. The formation constants for the interaction of complex I with different organic/inorganic anions in solution have also been studied by sandwich membrane method. PVC based membranes of I using tridodecylmethylammonium chloride (TDDMACl) as cation discriminator and o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), benzylacetate (BA) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as benzoate selective sensors. The best performance was shown by the membrane with composition (w/w) of I (5): PVC (150): NPOE (345): TDDMACl (0.3). The proposed sensor exhibits significantly enhanced selectivity toward benzoate ions over the concentration range 2.2×10−6–1.0×10−1 M with a lower detection limit of 1.4×10−6 M and a Nernstian slope of 59.2 mVdecade−1 of activity within a pH range of 4.5–8.5. The sensor has a response time of 12 s and can be used for at least 8 weeks without any considerable divergence in their potential response. The membrane sensor of complex I have been checked for reversible and accurate sensing of benzoate levels present in liquid food products.
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An alternative methodology for simultaneous analysis of aspartame (ASP), cyclamate (CYC), saccharin (SAC) and acesulfame-K (ACE) by capillary zone electrophoresis was developed and validated. Optimum separation conditions were achieved by evaluation of the effective mobility curve followed by background electrolyte (BGE) optimization through a full 32 factorial design. The optimized electrolyte composed of 20.0 mmol L−1 sodium tetraborate, 15.0 mmol L−1 Tris and 7.5 mmol L−1 benzoic acid (pH 9.15) was suitable for simultaneous direct (ASP, ACE and SAC) and indirect (CYC) UV detection at 215 nm. Method performance was evaluated for linearity (r > 0.992), precision (RSD%: <4.0%, ASP; <3.0%, CYC; <4.5%, SAC and <4.5%, ACE), accuracy (mean recovery range: 101.2%, ASP; 102.2%, CYC; 91.9%, SAC and 94.4%, ACE), detection limit (expressed in mg L−1: 6.80, ASP; 12.0, CYC; 0.50, SAC and 3.30, ACE) and quantification limit (expressed in mg L−1: 22.0, ASP; 40.0, CYC; 1.60, SAC and 10.0, ACE). Method applicability was demonstrated by analysis of lemon tea sachet samples containing ASP, CYC, SAC and ACE.
Article
The paper describes an optoelectronic device that has been designed and developed to measure the sulphite concentration in beverages for quality evaluation. A selective and sensitive method for determination of sulphite is based on the reaction with pararosaniline acid bleached dye and formaldehyde solution, which gives violet colored complex having absorption maxima at 560 nm. Lambert–Beer’s law is obeyed in the concentration range up to 25 μg/ml (25 ppm) of test solution within an accuracy of ±0.05μg/ml (0.05 ppm). The instrument involves the use of high intensity green light emitting diode (LED) of wavelength 565 nm as light source. BPW21 photodiode having the relative spectral sensitivity above 90% in the range of 500–600 nm has been used as a detector, for the determination of sulphite concentration.
Article
A single-step large phase ratio spontaneous extraction procedure followed by gas chromatography–mass spectrometry (GC–MS) was successfully applied for the determination of caffeine in beverages. Before the GC–MS analysis, as little as 25μL sample was spontaneously extracted with 1mL chloroform in a 2mL autosampler vial for 15min. The methodology exhibited excellent linearity in the range of 0.001–20mgL−1 with correlation coefficient of determination, r 2>0.9999 and a detection limit of 0.004mgL−1. Good repeatability of extraction performance was obtained with relative standard deviation lower than 2% and the recovery of the caffeine when spiked to three different brand beverages was in the range of 98.8–102.3%. The new application-oriented single-step spontaneous extraction method was fast, efficient, and is a good alternative to routine methods for caffeine analysis in beverages. KeywordsGas chromatography–mass spectrometry-Spontaneous extraction-Large phase ratio-Caffeine
Article
Capillary electrophoresis (CE) is a powerful microanalytical technique based on electrophoretic separation in narrow capillaries. The fast speed of analysis, high resolution and sensitivity make CE an attractive method to separate a wide range of charged and uncharged compounds, including substances of food interest. This review is organised into three parts. The first part deals with fundamental aspects of CE, specifically the relationships between migration time, electrophoretic and electroosmotic mobility in capillary zone electrophoresis (CZE). The second part focuses on the application of those principles to obtain separation of uncharged and charged species by Micellar Electrokinetic Chromatography (MEKC). In the third part the most recent works are reviewed on the application of different modes of CZE and MEKC for analysing natural and processed foods. A large selection of food components are covered, including carbohydrates, amino acids, proteins, colorants and dyestuffs, flavonoids and vitamins. A list of applications reported in Appendix A gives a further overview of the wide application area of CE in food analysis which have appeared in the two last years.
Article
Electrochemistry at the liquid-liquid interface enables the detection of nonredoxactive species with electroanalytical techniques. In this work, the electrochemical behavior of two food additives, aspartame and acesulfame K, was investigated. Both ions were found to undergo ion-transfer voltammetry at the liquid-liquid interface. Differential pulse voltammetry was used for the preparation of calibration curves over the concentration range of 30-350 microM with a detection limit of 30 microM. The standard addition method was applied to the determination of their concentrations in food and beverage samples such as sweeteners and sugar-free beverages. Selective electrochemically modulated liquid-liquid extraction of these species in both laboratory solutions and in beverage samples was also demonstrated. These results indicate the suitability of liquid-liquid electrochemistry as an analytical approach in food analysis.
Article
Full-text available
Separations can be applied to the analysis of soft drinks, artificial sweeteners, fruit juices, and coffee. Keywords (Audience): Second-Year Undergraduate
Article
Separation of complex carbohydrates is a rapidly developing area in capillary electrophoresis (CE). This method can be applied easily for fingerprinting labeled oligosaccharides, and it yields rapid, high-efficiency separations. A high degree of automation and microliter-level sample volume requirements make this method ideal for unattended and limited-sample environments. Scientists can use CE-based carbohydrate analysis to determine molar ratios and degree of polymerization of oligosaccharides and to detect changes in the extent or nature of the oligosaccharide distribution (fingerprinting) in modern biotechnology and food products.
Article
Methods for the determination of several organic acids commonly found in foods and beverages, including oxalic, citric, acetic, tartaric, malic, succinic, lactic, carbonic, aspartic, glutamic, ascorbic and gluconic acids, by capillary electrophoresis (CE) with indirect absorbance detection were developed. Several absorbance providers, including chromate, p-hydroxybenzoate, phthalate, terephthalate, trimellitate and pyromellitate, were investigated for their suitability as background electrolytes (BGEs). CE was performed in the negative voltage (reverse polarity, detector towards anode) mode. The effects of pH and various additives on CE separations were evaluated. The BGE and pH each played a major role in affecting the selectivity and resolution of CE. All analytes except malate and succinate could be baseline resolved in one run by performing CE with 5 mM trimellitate (as the BGE)-1 mM tetradecyltrimethylammonium bromide at pH 9.0 in less than 10 min. On the other hand, the CE separation of the tri- and dicarboxylic acids and hydroxydicarboxylic acids (the first five) could best be obtained at pH 5.5 in 5 min. The precision of the method for most monoprotic analytes is typically less than 1% for the migration time and 1–4% for the peak area (n = 6). The detection limit for most analytes is of the order of 2.0·10−6M. The new methods developed are rapid, sensitive and quantitative and can be readily applied to real food samples for quantitative analysis.
Article
Certain individuals may be sensitive to specific compounds in comsumer products. It is important to quantify these analytes in food products in order to monitor their intake. Caffeine is one such compound. Determination of caffeine in beverages by spectrophotometric procedures requires an extraction procedure, which can prove time-consuming. Although the corresponding determination by HPLC allows for a direct injection, capillary zone electrophoresis provides several advantages such as extremely low solvent consumption, smaller sample volume requirements, and improved sensitivity. Keywords (Audience): Second-Year Undergraduate
Article
Compares formulations of Coke and Pepsi and Diet Coke and Diet Caffeine-Free Coke. Keywords (Audience): Second-Year Undergraduate
Article
A method for the determination of the sulphite content in foods and beverages by capillary electrophoresis (CE) is described. The sulphite is converted to sulphur dioxide and finally to sulphate using a Monier-Williams distillation. The sulphate is then determined by CE using a 75 μm fused silica capillary column with a buffer consisting of 5 mm sodium chromate and 0.5 mM OFM Anion-BT reagent, pH 8.0, with indirect UV detection at 254 nm. Nitrate was used as the internal standard. The levels of sulphite in the products are in good agreement with those determined by titrimetry, except for one sample of fresh prawns, fresh garlic and some processed foods containing garlic and onion, where the levels determined by CE are lower. The instrument repeatability of the CE procedure is satisfactory and the level of detection is 5 mg/kg.
Article
Ascorbic acid (or vitamin C) is an important component of many biological systems and various physiological roles have been described for it. A rapid and simple capillary electrophoresis method for ascorbic acid measurements in biological fluids as well as in beverages was developed. A stereoisomer of ascorbic acid, isoascorbic acid, not normally found in nature, was used as the internal standard for this assay. The analysis was performed in a 30 cm x 75 microns I.D. fused-silica capillary with 100 mM tricine buffer, pH 8.8, and measured by UV absorbance at 254 nm. The method was sensitive to 1.6 micrograms/ml and linear to 480.1 micrograms/ml. Within-run R.S.D. was 3.2% (93.5 +/- 3.0 micrograms/ml, mean +/- S.D., n = 18) and run-to-run R.S.D. was 3.3% (35.6 +/- 1.2 micrograms/ml, mean +/- S.D., n = 10) and 1.9% (149.4 +/- 2.8 micrograms/ml, mean +/- S.D., n = 10). Average spiked recovery from human plasma samples was 98.0%. The technique has been demonstrated to be suitable for assay of vitamin C in biological samples and some fruit juices.
Article
Thermo-optical absorbance (TOA) detection using a KrF excimer waveguide laser for detection of benzoic acid, dehydroacetic acid and sorbic acid separated by capillary electrophoresis (CE) was studied. Detection limits were, on average, ten times better than those for on-column UV absorbance methods with CE, and two or more times better than those for UV absorbance with HPLC. The influence of increased laser power on TOA detection sensitivity was found to be strong for benzoic and dehydroacetic acids but quite weak for sorbic acid. It was discovered that photoisomerization of sorbic acid (2,4-hexadienoic acid) occurred readily in the detection volume at moderate laser powers (P(ave) = 3 mW) and increased with slow electroosmotic flows (< 6 cm/min). The TOA method described here shows improved detection sensitivity for CE analyses of compounds having only weak absorptivities (< 5% of maximum) at lambda = 248 nm, and thus demonstrates its utility for determination of a variety of analytes in a single separation.
Article
The application of capillary zone electrophoresis (CZE) in a hydrodynamically closed separation system to determine synthetic food colorants added to food products was investigated. The CZE separations were carried out in a 300-micron-i.d. capillary tube made of fluorinated ethylene-propylene copolymer. The inner diameter of the capillary tube made it possible to enhance sample loads (100-nL injection volumes) so that 10-300 ppb limits of detection (LOD) values could be achieved for the studied dyes by a photometric absorbance detector operating at a 254-nm detection wave-length. With the exception of erythrosine (which exhibited a residual adsorption), very good reproducibilities of the determination were typical for 4- and 32-ppm concentrations of the dyes. This rapid CZE procedure (migration times of the resolved analytes were between 2.5 and 10.5 min) provided good selectivities in the determination of the dyes in various food matrices (soft drink concentrates, liqueurs, and chewing gums). Simple sample preparation steps were effective for the sample matrices used in the investigation.