Vaughan S Langford

University of Canterbury, Christchurch, Canterbury, New Zealand

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Publications (17)30.23 Total impact

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    Vaughan S Langford, Ian Graves, Murray J McEwan
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    ABSTRACT: The gold standard for monitoring volatile organic compounds (VOCs) is gas chromatography/mass spectrometry (GC/MS). However, in many situations, when VOC concentrations are at the ppmv level, there are complicating factors for GC/MS. Selected ion flow tube mass spectrometry (SIFT-MS) is an emerging technique for monitoring VOCs in air. It is simpler to use and provides results in real time. Three different experiments were used for the comparison. First SIFT-MS was applied to monitor the concentrations of 25 VOCs in a mixture at concentrations up to 1 ppmv using only a generic database for known kinetic data of three reagent ions (H3 O(+) , NO(+) and O2 (+) ) with each VOC. In experiment 2, a side-by-side comparison was made of 17 VOCs at concentrations between 1 ppmv and 5 ppbv after small corrections had been made to the SIFT-MS kinetic data. In a third experiment, a side-by-side comparison examined two groups of samples received for commercial analysis. In experiment 1, 85% of the VOC concentrations were within 35% of their stated values without any calibration of the SIFT-MS instrument. In experiment 2, the two techniques yielded good correspondence between the measured VOC concentrations. In experiment 3, good correlation was found for VOCs from three of the samples. However, interferences from some product ions gave over-reported values in one sample from the SIFT-MS instrument. These three experiments showed that GC/MS was better suited to monitoring samples containing large numbers of VOCs at high concentrations. In all other applications, SIFT-MS proved simpler to use, was linear with concentration over a much wider concentration range than GC/MS and provided faster results. Copyright © 2013 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 01/2014; 28(1):10-18. · 2.51 Impact Factor
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    ABSTRACT: tThe ion-molecule chemistry of the three common reagent ions used in selected ion flow tube mass spec-trometry (SIFT-MS), H3O+, NO+and O2+, has been extended to include reactions with seven nitrosamines.Theoretical calculations enabled the dipole moments and polarizabilities of the nitrosamines studied tobe found and from these, the proton transfer rate coefficients have been calculated. In all cases rapid pro-ton transfer from H3O+occurred, and charge exchange and dissociative charge exchange were commonprocesses for NO+and O2+. For nitrosamines such as N-nitrosodibutylamine, noticeable fragmentationoccurred. When the helium carrier gas in the flow tube was changed to nitrogen, the technology stillgave good results for monitoring nitrosamines but the product channel ratios for some nitrosamineswere different for nitrogen than for helium. The new kinetic data obtained in this study was utilizedusing a commercial SIFT-MS instrument to monitor the production of N-nitrosodimethylamine andN-nitrosodiethylamine from heated salami.
    International Journal of Mass Spectrometry. 01/2014;
  • Vaughan S Langford, John D C Gray, Murray J McEwan
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    ABSTRACT: People are using increasing amounts of siloxanes that ultimately end up in landfills and then in landfill gas and biogas digesters. Their presence poses difficulties for industries seeking to utilize the energy content of landfill and biogas, as the combustion process oxidises silicon to silicon dioxide that in turn damages engine parts. Rapid, efficient and accurate methods are needed to quantify their presence. Selected ion flow tube mass spectrometry (SIFTMS) is an emerging real-time technique that has found application for monitoring trace volatiles in air. Samples containing the trace volatiles are simply drawn into the flow tube and convected in a stream of helium. Chemical ionization reactions from mass-selected reagent ions with the volatiles ensue. To quantify the volatiles in the sample, the ion chemistry of the reagent ion with each volatile must be known. Rate coefficients and product ion branching ratios were found for the compounds dodecamethylpentasiloxane, decamethylcyclopentasiloxane, decamethyltetrasiloxane, octamethylcyclotetrasiloxane, triethylsilanol, tetramethylsilane and hexamethyldisilazane. The ion-molecule reactions of the seven silicon-containing compounds examined here were fast, occurring at or near the collision rate, thus allowing for detection at low levels. The very simple reaction chemistry found of proton transfer, electron transfer and methyl loss will enable easy quantitation of the siloxanes in landfill gas and biogas using the SIFTMS technique. Copyright © 2013 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 03/2013; 27(6):700-6. · 2.51 Impact Factor
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    ABSTRACT: Increasing amounts of anthropogenic siloxane compounds are finding their way into landfills. The growing concentrations of siloxanes in landfill gas presents problems to the landfill and digester plant operators who seek to utilize methane production from the landfill or digester gas as an energy source. Results are presented for monitoring the reactions of SIFT-MS reagent ions H3O+, NO+ and O2 + with a number of the siloxanes, including hexamethyldisiloxane, C6H18OSi2, trimethylsilanol, C3H10OSi, octamethyltrisiloxane, C8H24O2Si3 and hexamethylcyclotrisiloxane, C6H18O3Si3. Collision rate reactions were assumed for the H3O+ ion and close to collision rate were found for the other two reagent ions. These results were then utilized to monitor siloxanes produced at three landfill sites. The SIFT-MS method was found to be simple to use, and fast without the need for sample pre-concentration.
    Current Analytical Chemistry 01/2013; 9(4). · 1.56 Impact Factor
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    ABSTRACT: Honeys have a range of physicochemical and organoleptic properties, depending on the nectar source. Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) is an emerging technology that quantifies volatile organic compounds (VOCs) to low concentrations (usually parts-per-trillion (ppt) levels) and is here applied to monitor the aromas in the headspace of different New Zealand monofloral honeys. Honey aromas arise from VOCs in the honeys that differ according to the flower type from which they were derived. In this exploratory study, the headspaces of nine monofloral New Zealand honeys (beech honeydew, clover, kamahi, manuka, rata, rewarewa, tawari, thyme, and vipers bugloss) were analyzed using SIFT-MS without sample preparation. The purpose of the investigation was to identify the major volatiles in each of the honeys and to test the feasibility of using SIFT-MS to distinguish between New Zealand monofloral honeys. In the nine monofloral honeys sampled, a clear distinction was observed between them based on their aroma signatures.
    Journal of Agricultural and Food Chemistry 06/2012; · 2.91 Impact Factor
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    ABSTRACT: New Zealand is a leader in the global dairy industry. Milk powder is the principal export product, but there is also a prominent cheese manufacturing industry, catering more for the domestic market. The Selected Ion Flow Tube-Mass Spectrometric (SIFT-MS) technique was used to compare 4 New Zealand cheeses marketed as "parmesan" with 4 Italian Parmigiano Reggiano and Grana Padano cheeses. The cheese headspace was analyzed in real time without any sample preconcentration. Total of 38 volatile compounds in the cheese headspace were monitored with headspace concentrations varying between single digit parts per billion (ppb) to tens of parts per million (ppm). When the results were subjected to multivariate statistical analysis, a clear discrimination was found between the New Zealand "parmesan" and Italian cheeses based solely on the measured concentrations of these volatile compounds. If the volatile compounds used in the analyses were restricted to known odor-active compounds in Parmigiano Reggiano cheese, the ability to discriminate between the cheeses was maintained. The analyses also showed that it was possible to clearly differentiate between the different processing plants in individual countries. Important discriminatory volatiles in the samples tested were butanoic acid and phenylacetaldehyde for discriminating between Italian cheeses and ethyl butyrate, acetaldehyde and methylbutanals between New Zealand cheeses. We conclude that the New Zealand "parmesans" do not provide a good representation of the aroma of Italian "parmesans." PRACTICAL APPLICATION: SIFT-MS has been shown to clearly differentiate both country of origin and the manufacturer of "parmesan" cheeses made in Italy and New Zealand based on differences in volatile organic compounds. Thus this method will have benefit for use in the quality control of "parmesan" and other cheese varieties.
    Journal of Food Science 05/2012; 77(6):C719-26. · 1.78 Impact Factor
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    ABSTRACT: Vanilla beans have been shown to contain over 200 compounds, which can vary in concentration depending on the region where the beans are harvested. Several compounds including vanillin, p-hydroxybenzaldehyde, guaiacol, and anise alcohol have been found to be important for the aroma profile of vanilla. Our objective was to evaluate the performance of selected ion flow tube mass spectrometry (SIFT-MS) and Fourier-transform infrared (FTIR) spectroscopy for rapid discrimination and characterization of vanilla bean extracts. Vanilla extracts were obtained from different countries including Uganda, Indonesia, Papua New Guinea, Madagascar, and India. Multivariate data analysis (soft independent modeling of class analogy, SIMCA) was utilized to determine the clustering patterns between samples. Both methods provided differentiation between samples for all vanilla bean extracts. FTIR differentiated on the basis of functional groups, whereas the SIFT-MS method provided more specific information about the chemical basis of the differentiation. SIMCA's discriminating power showed that the most important compounds responsible for the differentiation between samples by SIFT-MS were vanillin, anise alcohol, 4-methylguaiacol, p-hydroxybenzaldehyde/trimethylpyrazine, p-cresol/anisole, guaiacol, isovaleric acid, and acetic acid. ATR-IR spectroscopy analysis showed that the classification of samples was related to major bands at 1523, 1573, 1516, 1292, 1774, 1670, 1608, and 1431 cm(-1) , associated with vanillin and vanillin derivatives.
    Journal of Food Science 03/2012; 77(3):C284-92. · 1.78 Impact Factor
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    ABSTRACT: The selectivity and sensitivity of selected ion flow tube mass spectrometry (SIFT-MS) for individual breath analysis of haloamines has been improved by heating the flow tube in a commercial instrument to around 106 degrees C. Data is presented showing the marked reduction in the number density of water clusters of product ions of common breath metabolites that are isobaric with the product ions from monochloramine and monobromamine that are used to monitor the haloamine concentrations. These results have direct relevance to the real-time monitoring of chloramines in drinking water, swimming pools and food processing plants. However, once the isobaric overlaps from water cluster ions are reduced at the higher temperatures, there is no conclusive evidence showing the presence of haloamines on single breath exhalations in the mid parts per trillion range from examination of the breaths of volunteers.
    Rapid Communications in Mass Spectrometry 06/2010; 24(12):1744-8. · 2.51 Impact Factor
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    ABSTRACT: The on-line detection of gaseous peroxyacetyl nitrate (PAN) using selected ion flow tube mass spectrometry (SIFT-MS) has been investigated using a synthetic sample of PAN in air at a humidity of approximately 30%. Using the H(3)O(+) reagent ion, signals due to PAN at m/z 122, 77 and 95 have been identified. These correspond to protonated PAN, protonated peractetic acid and its water cluster, respectively. These products and their energetics have been probed through quantum mechanical calculations. The rate coefficient of H(3)O(+) has been estimated to be 4.5 x 10(-9) cm(3) s(-1), leading to a PAN sensitivity of 138 cps/ppbv. This gives a limit of detection of 20 pptv in 10 s using the [M+H](+) ion of PAN at m/z 122.
    Rapid Communications in Mass Spectrometry 02/2010; 24(3):343-8. · 2.51 Impact Factor
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    ABSTRACT: In the atmosphere, peroxyacetylnitrate (PAN) is produced from the reaction of peroxyacetyl radicals with NO2 and arises from the oxidation chemistry of hydrocarbons leading to tropospheric ozone. Its importance as a nitrogen reservoir, an eye and respiratory irritant and a plant phytotoxin means that its ambient measurement remains an integral part of both the long term and intensive measurement campaigns necessary for understanding this chemistry. We have been investigating the use of SIFT-MS to measure PAN in real time along with a number of atmospherically relevant organic compounds. The low pressures and near ion thermal energies of the SIFT-MS allows the efficient protonation of PAN and the simple real time measurement of its concentration. While PAN, and its analogues, are routinely measured using dedicated GC based systems, the use of SIFT-MS would give fast response real time measurements without the need for a dedicated instrument. The methodology and preliminary summertime ambient measurements will be presented.
    04/2009;
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    ABSTRACT: Aldehydes and ketones are the first generation products of atmospheric hydrocarbon oxidation. As such their measurement is a key component in the testing of our current understanding of atmospheric chemistry leading to ozone production. Trap and analyse methods have been successful for analyzing these species but the rapid chemistry of their production and loss drives the need for measurements on the minute time scale. Mass spectrometric methods have the advantage of wide applicability to the hydrocarbons and the carbonyl compounds with fast time response. However, since this is fundamentally a mass measurement, these methods often cannot distinguish between structural isomers on the basis of the parent ion alone. This is a particular problem for the carbonyl compounds such as methacrolein and methylvinyl ketone produced from the oxidation of isoprene as the aldehyde and ketone have the same mass. SIFT-MS is a mass spectrometric method that uses three different reagent ions, H3O+, NO+ and O2+ for chemical ionization of ambient samples. While the reaction of structural isomers with H3O+ produces the same parent ion, the reactions with the other reagent ions are different allowing rapid, real time measurements of structurally isomeric carbonyls. We will discuss the methodology of this technique and some preliminary ambient measurements taken in a small city.
    04/2009;
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    ABSTRACT: Selected ion flow tube mass spectrometry (SIFT-MS) is a technique that offers real-time alternatives to existing methods for monitoring hazardous air pollutants (HAPs) in the environment using chemical ionization. The use of this technique requires knowledge of the kinetic parameters of the reagent ions H(3)O(+), NO(+), and O(2)(+) that are most commonly used. We report here measurements with these reagent ions of kinetic parameters for 17 HAP molecules ranging from 1,1-dichloroethene to nitrobenzene. From these data, limits of quantitation are established for all 17 compounds on a commercial SIFT-MS instrument and are found to be well below the time-weighted averages required by legislating bodies for workplace conditions.
    Analytical Chemistry 02/2009; 81(4):1595-9. · 5.70 Impact Factor
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    ABSTRACT: The rate coefficients of the ion–molecule reactions between O2+, H3O+, and a range of linear saturated hydrocarbons, and between common hydrocarbon product ions from these reactions and water were determined using a flowing afterglow selected ion flow tube mass spectrometer. Using these data, the selected ion flow tube-mass spectrometry (SIFT-MS) technique was applied to the real-time measurement of linear saturated hydrocarbons in dry and moist headspace samples without sample preparation. Using a Voice100 SIFT-MS instrument the Geochemical VOC method (GeoVOC) has been assessed against calibrated standards and found to give an experimental RMS precision to within 2% for dry and 6% for humid hydrocarbon samples in the ppm range. The application of SIFT-MS and development of the GeoVOC method offers a fast convenient means of assessment of hydrocarbon seeps.
    International Journal of Mass Spectrometry. 01/2007; 268(1):38-46.
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    Article: GeoVOC
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    ABSTRACT: The rate coefficients of the ion-molecule reactions between O2+, H3O+, and a range of linear saturated hydrocarbons, and between common hydrocarbon product ions from these reactions and water were determined using a flowing afterglow selected ion flow tube mass spectrometer. Using these data, the selected ion flow tube-mass spectrometry (SIFT-MS) technique was applied to the real-time measurement of linear saturated hydrocarbons in dry and moist headspace samples without sample preparation. Using a Voice100 SIFT-MS instrument the Geochemical VOC method (GeoVOC) has been assessed against calibrated standards and found to give an experimental RMS precision to within 2% for dry and 6% for humid hydrocarbon samples in the ppm range. The application of SIFT-MS and development of the GeoVOC method offers a fast convenient means of assessment of hydrocarbon seeps.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2007;
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    ABSTRACT: We compared the performance of the BacT/ALERT automated blood culture system with real-time, quantitative volatile organic compound (VOC) detection by selected ion flow tube-mass spectrometry (SIFT-MS). Blood samples from healthy donors were artificially infected with 5 or 100 CFU of organisms commonly causing bacteremia. Positive results by SIFT-MS analysis of headspace gases were recorded for 53/60 (88.3%) bottles at 8h, and 58/60 (96.6%) bottles at 24 h. We conclude that SIFT-MS is a sensitive method for the detection of microbial VOCs. Furthermore, profiles of the VOCs detected may allow simultaneous identification of infecting organisms.
    Journal of Microbiological Methods 07/2006; 65(3):628-31. · 2.16 Impact Factor
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    ABSTRACT: To achieve faster bacteremia diagnosis, selected ion flow tube mass spectrometry (SIFT-MS) measured metabolic gases in the headspaces of BacT/ALERT blood culture bottles. Pseudomonas aeruginosa, Streptococcus pneumoniae, Escherichia coli, Staphylococcus aureus and Neisseria meningitidis growth and trace gas patterns were detected from 10 colony forming units after 6 h.
    Journal of Microbiological Methods 06/2006; 65(2):361-5. · 2.16 Impact Factor
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    ABSTRACT: We describe a new method, Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) for the rapid and sensitive real-time detection and quantification of volatile organic compounds from medically important fungi, grown on a range of laboratory media. SIFT-MS utilises the chemical ionisation reactions of mass-selected ions to characterise volatile organic compounds (VOCs) that are produced as metabolites from fungi. This technique has the distinct advantage over others in that it readily detects low molecular weight, reactive volatiles, and allows for real-time, quantitative monitoring. The fungi examined in this study were Aspergillus flavus, Aspergillus fumigatus, Candida albicans, Mucor racemosus, Fusarium solani, and Cryptococcus neoformans grown on or in malt extract agar, Columbia agar, Sabouraud's dextrose agar, blood agar, and brain-heart infusion broth. Common metabolites (ethanol, methanol, acetone, acetaldehyde, methanethiol, and crotonaldehyde) were detected and quantified. We found the fingerprint of volatiles, in terms of presence and quantity of volatiles to be strongly dependent on the culture medium, both in terms of variety and quantity of volatiles produced, but may form the basis for species specific identification of medically important fungi.
    Journal of Microbiological Methods 12/2005; 63(2):127-34. · 2.16 Impact Factor