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With the establishment by CODEX of a 200 ng/g limit of inorganic arsenic (iAs) in polished rice grain, more analyses of iAs will be necessary to ensure compliance in regulatory and trade applications, to assess quality control in commercial rice production, and to conduct research involving iAs in rice crops. Although analytical methods using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) have been demonstrated for full speciation of As, this expensive and time-consuming approach is excessive when regulations are based only on iAs. We report a streamlined sample preparation and analysis of iAs in powdered rice based on heated extraction with 0.28 M HNO 3 followed by hydride generation (HG) under control of acidity and other simple conditions. Analysis of iAs is then conducted using flow-injection HG and inexpensive ICP-atomic emission spectroscopy (AES) or other detection means. A key innovation compared with previous methods was to increase the acidity of the reagent solution with 4 M HCl (prior to reduction of As 5+ to As 3+ ), which minimized interferences from dimethylarsinic acid. An inter-laboratory method validation was conducted among 12 laboratories worldwide in the analysis of six shared blind duplicates and a NIST Standard Reference Material involving different types of rice and iAs levels. Also, four laboratories used the standard HPLC-ICP-MS method to analyze the samples. The results between the methods were not significantly different, and the Horwitz ratio averaged 0.52 for the new method, which meets official method validation criteria. Thus, the simpler, more versatile, and less expensive method may be used by laboratories for several purposes to accurately determine iAs in rice grain. Graphical abstract Comparison of iAs results from new and FDA methods.

This chapter describes an easy, rapid, and low-cost sample preparation approach for the determination of pesticide residues in foods using gas and/or liquid chromatographic (GC and/or LC) analytical separation and mass spectrometric (MS) detection. The approach is known as QuEChERS, which stands for "quick, easy, cheap, effective, rugged, and safe." Originally, QuEChERS was a particular "method" for pesticide residue analysis, but it is very flexible and has evolved into an "approach," which has been used in many methods, and not just for pesticide residues. Two of the QuEChERS versions using buffering have been validated in interlaboratory trials for dozens of pesticides in several food matrices, and both have successfully met performance criteria to achieve "official" status from international standard organizations (AOAC Official Method 2007.01 and CEN Standard Method EN 15662). The main aspects of the QuEChERS approach consists of extraction of a well-homogenized sample by shaking with solvent (typically acetonitrile) in a centrifuge tube, salt-out partitioning of water with salts including magnesium sulfate (MgSO(4)), and cleanup using "dispersive solid-phase extraction" (dSPE), in which common matrix components are retained by sorbent(s) and the analytes remain in the extract. For widest analytical scope, concurrent analysis is done for hundreds of pesticides using GC-MS(/MS) and LC-MS/MS. The aim of this chapter is to review the QuEChERS sample preparation methodology and provide a summary of up-to-date information with modification options depending on the application needs.

At the 123rd AOAC International Annual Meeting in Philadelphia, PA, 45 residue chemists gathered for a roundtable discussion of mass spectrometry (MS) used for regulatory chemical residues analysis. The session was conceived to address current technical and communication issues about MS between "bench chemists and their bosses". The topics covered a range of practical, routine, and recurring issues on capabilities and limitations of MS techniques, and suggestions on how chemists may better communicate their MS results with customers. The customers in this sense include laboratory managers, quality assurance officers, laboratory clients, regulatory officials, policy-makers, lawyers, and others who have interest in the data. The stated goals devised by the roundtable panelists were to provide independent advice, describe limitations, give practical tips, help set realistic expectations, and answer questions from the attendees. The panelists divided the topics into three main themes: practical aspects in routine analysis using MS, choice of MS technique depending on the purpose for analysis, and qualitative identification and confirmation concepts. This report was written to summarize and expand upon the discussion, frame the current issues, and provide advice on handling common situations in MS analysis and reporting of results. Topics included LODs, data quality objectives, quantification and reporting results, matrix effects, calibration, terminology, differences in performance across MS platforms, proficiency testing, qualitative analysis, and laboratory accreditation. Conclusions are presented as a set of questions for structuring a dialog between bench chemists and laboratory managers.

Most analytical methods for persistent organic pollutants (POPs) focus on individual groups of targeted analytes. Therefore, analysis of multiple classes of POPs typically entails several sample preparations, fractionations, and injections, whereas other chemicals of possible interest are neglected or lost. To analyze a wider scope of organic contaminants in fish oil, we developed an approach to combine the analysis of targeted and untargeted chemicals using an automated direct sample introduction (DSI) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC x GC/ ToF-MS). DSI-GC x GC/ToF-MS is a powerful tool that attains high quality separations to achieve high selectivity while still providing a wide analytical scope with minimal sample preparation, especially in conjunction with DSr's high tolerance to dirty extracts. Gel permeation chromatography (GPC) was used for initial separation of lipids from POPs and other GC-amenable organic compounds from dietary cod liver oil. For comparison purposes, additional cleanup of the GPC extracts was done by silica adsorption and acidification, which helped provide clues in the identification of untargeted compounds, but in routine analysis, only GPC is needed for this analytical approach. The approach allowed simultaneous identification of known-POPs in the fish liver oils, and further permitted presumptive identifications of multiple groups of halogenated natural products (HNPs) and other organic chemicals of interest through comparisons of the mass spectra from analyses with those from mass spectral libraries and/or reports in the literature (approximately 60 PCB congeners and 76 compounds in total). Subsequent confirmations were made by reanalysis and comparison of chromatographic retention times and mass spectra with contemporaneously analyzed reference standards. Otherwise, ion fragmentation patterns of unknown compounds were assessed for tentative identifications. Some of the HNPs in the fish oils were detected and identified for the first time. Our study demonstrates that the wide monitoring scope provided by the DSI-GC x GC/ToF-MS method after GPC provides many logistical and performance advantages over the conventional use of several different methods designed for individual classes of targeted analytes after extensive sample preparation.

The 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are among the most toxic compounds known, and several sources of exposure to these chemicals should be monitored to protect human and environmental health. The current predominant method of analysis is too expensive and cumbersome, and comprehensive two-dimensional GC coupled to time-of-flight mass spectrometry (GC x GC--TOF-MS) has the potential to lower the costs and speed analysis of PCDD/Fs. In this study, GC x GC--TOF parameters were evaluated and optimized to yield complete separation of the 17 most important PCDD/F congeners from polychlorinated biphenyls (PCBs) interferences, and to attain the lowest detection limits. The optimization study entailed evaluation of oven temperature programs, column flow rates, ion source temperatures, electron ionization energy, data acquisition rate, and various GC x GC parameters, including modulation period, modulator temperature offset and hot pulse duration. After optimization, all 17 PCDD/Fs were separated in <60 min, and in particular, the critical pair of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and pentachlorobiphenyl congener CB126 did not co-elute chromatographically. Accurate identification and determination of all analytes could be made using their deconvoluted full mass spectra. In GC x GC, the modulation period and start time were the most important factors that affected sensitivity and selectivity for the analysis of the PCDD/Fs. The modulation period should be < or = 4s to preserve separations achieved in one-dimensional GC, and the modulation start time was important to achieve one large slice and two smaller symmetrical slices of TCDD to maximize its detection sensitivity. After optimization, the method could identify 0.25 pg of TCDD with standard injection from its full mass spectrum.

A fast and easy sample preparation procedure for analysis of acrylamide in various food matrices was developed and optimized. In its first step, deuterated acrylamide internal standard is added to 1 g of homogenized sample together with 5 mL of hexane, 10 mL of water, 10 mL of acetonitrile, 4 g of MgSO4, and 0.5 g of NaCl. Water facilitates the extraction of acrylamide; hexane serves for sample defatting; and the salt combination induces separation of water and acetonitrile layers and forces the majority of acrylamide into the acetonitrile layer. After vigorous shaking of the extraction mixture for 1 min and centrifugation, the upper hexane layer is discarded and a 1 mL aliquot of the acetonitrile extract is cleaned up by dispersive solid-phase extraction using 50 mg of primary secondary amine sorbent and 150 mg of anhydrous MgSO4. The final extract is analyzed either by liquid chromatography-tandem mass spectrometry or by gas chromatography-mass spectrometry (in positive chemical ionization mode) using the direct sample introduction technique for rugged large-volume injection.

Nitrofurazone usage in food‐producing animals is prohibited in most countries, including the United States. Regulatory agencies regularly monitor its use in domestic, export/import animals' food products by measuring the semicarbazide (SEM) metabolite as a biomarker of nitrofurazone exposure. However, the use of SEM is controversial because it is also produced in food naturally and thus gives false positive results. A cyano‐metabolite, 4‐cyano‐2‐oxobutyraldehyde semicarbazone (COBS), is proposed as an alternate specific marker of nitrofurazone to distinguish nitrofurazone from treated or untreated animals. A synthetic method was developed to produce COBS via metallic hydrogenation of nitrofurazone. The product was isolated and characterized by one‐ and two‐dimensional nuclear magnetic spectroscopy (NMR) experiments, Fourier‐transform infrared spectroscopy (FT‐IR), and mass spectrometry. The developed synthetic procedure was further extended to synthesize isotopically labeled 4‐[13C]‐cyano‐2‐oxo‐ [2, 3, 4‐13C3]‐butyraldehyde semicarbazone. Labeled COBS is useful as an internal standard for its quantification in food‐producing animals. Thus, the developed method provides a possibility for its commercial synthesis to procure COBS. This is the first synthesis of the alternate specific marker metabolite of nitrofurazone for possible usage in regulatory analysis to solve a real‐world problem. [ABSTRACT FROM AUTHOR]

The concept of low pressure (LP) vacuum outlet gas chromatography (GC) was introduced more than 50 years ago, but it was not until the 2000s that its theoretical applicability to fast analysis of GC-amenable chemicals was realized. In practice, LPGC is implemented by placing the outlet of a short, wide (typically 10–15 m, 0.53 mm inner diameter) analytical column under vacuum conditions, which speeds the separation by reducing viscosity of the carrier gas, thereby leading to a higher optimal flow rate for the most separation efficiency. To keep the inlet at normal operating pressures, the analytical column is commonly coupled to a short, narrow uncoated restriction capillary that also acts as a guard column. The faster separations in LPGC usually result in worse separation efficiency relative to conventional GC, but selective detection usually overcomes this drawback. Mass spectrometry (MS) provides highly selective and sensitive universal detection, and nearly all GC-MS instruments provide vacuum outlet conditions for implementation of LPGC-MS(/MS) without need for adaptations. In addition to higher sample throughput, LPGC provides other benefits, including lower detection limits, less chance of analyte degradation, reduced peak tailing, increased sample loadability, and more ruggedness without overly narrow peaks that would necessitate excessively fast data acquisition rates. This critical review summarizes recent developments in the application of LPGC with MS and other detectors in the analysis of pesticides, environmental contaminants, explosives, phytosterols, and other semi-volatile compounds. [ABSTRACT FROM AUTHOR]

Although quantitative analytical methods must be empirically validated prior to their use in a variety of applications, including regulatory monitoring of chemical adulterants in foods, validation of qualitative method performance for the analytes and matrices of interest is frequently ignored, or general guidelines are assumed to be true for specific situations. Just as in the case of quantitative method validation, acceptable method performance criteria should be established for qualitative analysis purposes to suit the analytical needs for given applications, and empirical method validation should be conducted to demonstrate the qualitative performance capabilities the method. This critical review article is intended to describe and discuss recent developments with of respect to qualitative aspects in mass spectrometry, and to make recommendations for validation of qualitative methods that meet common needs for monitoring of chemical contaminants in foods. [ABSTRACT FROM AUTHOR]

RATIONALE: Analysis for identification and quantification of regulated veterinary drug residues in foods is usually achieved by liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS). The instrumental method requires the selection of characteristic ions, but structural elucidation is seldom performed to help ensure accuracy. This study is a continuation of previous work to characterize selected product ions in support of regulatory monitoring programs. METHODS: The tandem mass spectra of 28 veterinary drugs from a previously published LC/MS/MS method were acquired with a high-resolution quadrupole time-of-flight (Q-TOF) mass spectrometer using electrospray ionization (ESI) in positive mode. The TOF analyzer was calibrated to achieve a mass accuracy error <5ppm for the MS and MS/MS modes, and samples were infused for data acquisition. RESULTS: The high mass accuracy achieved in Q-TOF allowed elucidation of the formulae of the product ions previously selected for qualitative identification. Rational interpretation of results was made and compared with the published literature, and the structure for the MS/MS product ions of four classes of regulated drugs (mectins, benzimidazoles, nitroimidazoles, and phenothiazines), totaling 28 compounds, were examined leading to the report of new structures or confirmation of published structures using low-resolution MS. CONCLUSIONS: Structural characterization of the product ions selected for identification and quantification of veterinary drug residues is important information for regulatory monitoring programs in defense of regulatory enforcement actions. This study has allowed structural elucidation of 84 MS/MS product ions previously selected for the LC/MS/MS analysis of 28 drug analytes. Published in 2015. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

This study analysed 22 strawberry and soil samples after their collection over the course of 2 years to compare the residue profiles from organic farming with integrated pest management practices in Portugal. For sample preparation, we used the citrate-buffered version of the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. We applied three different methods for analysis: (1) 27 pesticides were targeted using LC-MS/MS; (2) 143 were targeted using low pressure GC-tandem mass spectrometry (LP-GC-MS/MS); and (3) more than 600 pesticides were screened in a targeted and untargeted approach using comprehensive, two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOF-MS). Comparison was made of the analyses using the different methods for the shared samples. The results were similar, thereby providing satisfactory confirmation of both similarly positive and negative findings. No pesticides were found in the organic-farmed samples. In samples from integrated pest management practices, nine pesticides were determined and confirmed to be present, ranging from 2 µg kg−1for fluazifop-p-butyl to 50 µg kg−1for fenpropathrin. Concentrations of residues in strawberries were less than European maximum residue limits. [ABSTRACT FROM AUTHOR]

Abstract: This article describes the comparison of different versions of an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits and vegetables by concurrent use of gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) for detection. The sample preparation approach is known as QuEChERS, which stands for “quick, easy, cheap, effective, rugged and safe”. The three compared versions were based on the original unbuffered method, which was first published in 2003, and two interlaboratory validated versions: AOAC Official Method 2007.01, which uses acetate buffering, and European Committee for Standardization (CEN) Standard Method EN 15662, which calls for citrate buffering. LC–MS/MS and GC–MS analyses using each method were tested from 50 to 1000ng/g in apple–blueberry sauce, peas and limes spiked with 32 representative pesticides. As expected, the results were excellent (overall average of 98% recoveries with 10% RSD) using all 3 versions, except the unbuffered method gave somewhat lower recoveries for the few pH-dependent pesticides. The different methods worked equally well for all matrices tested with equivalent amounts of matrix co-extractives measured, matrix effects on quantification and chemical noise from matrix in the chromatographic backgrounds. The acetate-buffered version gave higher and more consistent recoveries for pymetrozine than the other versions in all 3 matrices and for thiabendazole in limes. None of the versions consistently worked well for chlorothalonil, folpet or tolylfluanid in peas, but the acetate-buffered method gave better results for screening of those pesticides. Also, due to the recent shortage in acetonitrile (MeCN), ethyl acetate (EtOAc) was evaluated as a substitute solvent in the acetate-buffered QuEChERS version, but it generally led to less clean extracts and lower recoveries of pymetrozine, thiabendazole, acephate, methamidophos, omethoate and dimethoate. In summary, the acetate-buffered version of QuEChERS using MeCN exhibited advantages compared to the other tested methods in the study. [Copyright &y& Elsevier]

Abstract: A quantitative answer cannot exist in analysis without a qualitative component to give enough confidence that the result meets the analytical needs (i.e. the result relates to the analyte and not something else). Just as a quantitative method must typically undergo an empirical validation process to demonstrate that it is fit for purpose, qualitative methods should also empirically demonstrate that they are suitable to meet the analytical needs. However, thorough qualitative method validation requires analysis of a great number of samples (possibly more than can be reasonably done), which is generally avoided due to the time and the effort involved. Instead, mass spectrometry (MS) is generally assumed to be the gold standard for qualitative methods, and its results are typically unquestioned. For example, a system was developed by European regulators of veterinary drug residues in food animals (2002/657/EC), in which the number of identification points given in MS analyses depends on the general degree of selectivity of the MS technique used. This well-defined approach gives a definite answer for decision-makers, so it has grown in popularity. However, the identification-points system is not scientific. The reality is that each situation requires information gathering and careful deductive thinking on the part of the analyst to make MS identifications. Rather than devise arbitrary requirements that need to be met by an unthinking analyst, we remind the analytical community that confirmation can be given only if two or more independent analyses are in agreement, preferably using orthogonally selective (independent) chemical mechanisms. In this article, we discuss the proper use of terminology, highlight the identification power of various MS techniques, demonstrate how MS identifications can fail if precautions are not taken, and re-assert the value of basic confirmation practices, qualitative method validation, information checklists, routine quality-control procedures, and blind proficiency-test analyses. [Copyright &y& Elsevier]

Analyte protectants were previously defined as compounds that strongly interact with active sites in the gas chromatographic (GC) system, thus decreasing degradation, adsorption, or both of coinjected analytes. In this study, we evaluated various combinations of promising analyte protectants for the volatility range of GC-amenable pesticides using GC/quadrupole mass spectrometry (MS) and 1-μL hot splitless injection for sample introduction. A mixture of ethylglycerol, gulonolactone, and sorbitol (at 10, 1, and 1 mg/mL, respectively, in the injected samples) was found to be the most effective in minimizing losses of susceptible analytes and significantly improving their peak shapes (due to reduction of peak tailing). When added to final sample extracts and matrix-free calibration standards alike, these analyte protectants induced a similar response enhancement in both instances, resulting in effective equalization of the matrix-induced response enhancement effect even after a large number of fruit and vegetable extract injections. As compared to matrix-matched standardization, the analyte protectant approach offers a more convenient solution to the problems associated with calibration in routine GC/MS analysis of pesticide residues and possibly other susceptible analyte types in diverse samples. Moreover, the use of analyte protectants also substantially reduced another adverse matrix-related effect caused by gradual build-up of nonvolatile matrix components in the GC system, thus improving ruggedness and, consequently, reducing need for frequent maintenance. [ABSTRACT FROM AUTHOR]

Evaluates two rapid methods of sample preparation and analysis of fatty foods. Comparison of pesticide residues representing a wide range of physicochemical properties; Concurrent analysis of extracts in both methods by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry; Recoveries of semi-polar and polar pesticides for both methods.

Examines a modification that entails the use of buffering during extraction to further improve results for certain problematic pesticides in a method for the determination of pesticides in produce. Extraction of samples with acetonitrile; Concurrent analysis by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry; Evaluation of the method for diverse pesticides in different matrixes.

Studies the validity of a method for the determination of pesticides in fruits and vegetables. Results of validation experiments; Sample extraction involved in the method; Analysis by gas chromatography and mass spectrometry.

Fast gas chromatography–mass spectrometry (GC–MS) has the potential to be a powerful tool in routine analytical laboratories by increasing sample throughput and improving laboratory efficiency. However, this potential has rarely been met in practice because other laboratory operations and sample preparation typically limit sample throughput, not the GC–MS analysis. The intent of this article is to critically review current approaches to fast analysis using GC–MS and to discuss practical considerations in addressing their advantages and disadvantages to meet particular application needs. The practical ways to speed the analytical process in GC and MS individually and in combination are presented, and the trade-offs and compromises in terms of sensitivity and/or selectivity are discussed. Also, the five main current approaches to fast GC–MS are described, which involve the use of: (1) short, microbore capillary GC columns; (2) fast temperature programming; (3) low-pressure GC–MS; (4) supersonic molecular beam for MS at high GC carrier gas flow; and (5) pressure-tunable GC–GC. Aspects of the different fast GC–MS approaches can be combined in some cases, and different mass analyzers may be used depending on the analytical needs. Thus, the capabilities and costs of quadrupole, ion trap, time-of-flight, and magnetic sector instruments are discussed with emphasis placed on speed. Furthermore, applications of fast GC–MS that appear in the literature are compiled and reviewed. At this time, the future usefulness of fast GC–MS depends to some extent upon improvement of existing approaches and commercialization of interesting new techniques, but moreover, a greater emphasis is needed to streamline overall laboratory operations and sample preparation procedures if fast GC–MS is to become implemented in routine applications. [Copyright &y& Elsevier]

Gas chromatography (GC) is used widely in applications involving food analysis. Typical applications pertain to the quantitative and/or qualitative analysis of food composition, natural products, food additives, flavor and aroma components, a variety of transformation products, and contaminants, such as pesticides, fumigants, environmental pollutants, natural toxins, veterinary drugs, and packaging materials. The aim of this article is to give a brief overview of the many uses of GC in food analysis in comparison to high-performance liquid chromatography (HPLC) and to mention state-of-the-art GC techniques used in the major applications. Past and current trends are assessed, and anticipated future trends in GC for food applications are predicted. Among the several new techniques being developed, the authors believe that, in food analysis applications, fast-GC/mass spectrometry (MS) will have the most impact in the next decade. Three approaches to fast-GC/MS include low-pressure GC/MS, GC/time-of-flight (TOF)-MS and GC/supersonic molecular beam (SMB)-MS, which are briefly discussed, and their features are compared. [Copyright &y& Elsevier]

• We report the novel and useful LTM-LPGC-MS technique for the first time. • A new working instrument for real-world application was developed. • LTM-LPGC-MS concepts, features, and trade-offs are described and evaluated. • Example applications with <1 min analysis cycle times are demonstrated. • Comparison of LTM-LPGC-MS is made with conventional fast GC-MS. Conventional gas chromatography - mass spectrometry (GC-MS) takes 20–40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as "LTM Fast GC" that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs. [ABSTRACT FROM AUTHOR]

Structural isomeric pesticides are used in agriculture and may be challenging to differentiate for accurate identification in pesticide monitoring programs. Due to structural similarity, isomeric pesticides are difficult to separate chromatographically, and thus, their accurate identification may rely solely on mass spectrometric analysis (MS). In this study, we challenged the ability of high-resolution quadrupole-orbitrap (Q-Orbitrap) mass spectrometry to produce and evaluate the tandem mass spectrometry (MS/MS) product ions for the selected five pairs of isomeric pesticides from different classes: Pebulate and vernolate, methiocarb and ethiofencarb, uniconazole and cyproconazole, sebuthylazine and terbuthylazine, and orbencarb and thiobencarb. The use of Q-Orbitrap instrument with a mass error <3 ppm allowed proposed elucidation of the product ion structures with consideration of the ion formulae, data interpretation, and literature searches. Product ions unique to pebulate, vernolate, methiocarb, ethiofencarb, and uniconazole were observed. Elucidation of the observed MS/MS product ion structures was conducted, and the fragmentation pathways were proposed. This information is valuable to increase selectivity in MS/MS analysis and differentiate isomeric pesticides, and thereby reduce the rates of false positives in pesticide monitoring programs. [ABSTRACT FROM AUTHOR]

Abstract: Gas chromatography–mass spectrometry (GC–MS) instrument limit of detection (LOD) is typically listed by major vendors as that of octafluoronaphthalene (OFN). Most current GC–MS instruments can achieve LODs in the low femtogram range. However, GC–MS LODs for realistic analytes in actual samples are often a few orders of magnitude higher than OFN''s. Users seldom encounter 1pg LOD in the single ion monitoring mode in their applications. We define this detectability difference as the “OFN gap.” In this paper, we demonstrate and discuss how the OFN gap can be significantly reduced by the use of GC–MS with supersonic molecular beams (SMB). Experimental results were obtained with a recently developed GC–MS with SMB named 1200-SMB, that is based on the conversion of the Varian 1200 system into a GC–MS–MS with SMB. With this 1200-SMB system, the LOD of all types of analytes, including OFN, in real samples is significantly improved through the combination of: (a) enhanced molecular ion; (b) elimination of vacuum background noise; (c) elimination of mass independent noise; (d) elimination of ion source peak tailing and degradation; (e) significantly increased range of thermally labile and low volatility compounds that are amenable for analysis through lower sample elution temperatures; (f) reduced column bleed and ghost peaks through sample elution at lower temperatures; (g) improved compatibility with large volume injections; and (h) reduced matrix interferences through the combination of enhanced molecular ion and MS–MS. As a result, the 1200-SMB LODs of common and/or difficult compounds are much closer to its OFN LOD, even in complex matrices. We crossed the <1fg OFN LOD milestone to achieve the lowest LOD to date using GC–MS, but more importantly, we attained LOD of 2fg for diazinon, a common pesticide analyte. In another example, we achieved an LOD of 10fg for underivatized testosterone, which is not amenable in traditional GC–MS analysis, and conducted many analyses of naturally incurred testosterone in alligator blood extracts. In comparison with standard GC–MS, we measured detectability enhancement factors of 24 for dimethoate, 30 for methylstearate, 50 for cholesterol, 50 for permethrin, >400 for methomyl, and >2000 for C32H66. In general, the harder the compound analysis, the greater is the gain in sample detectability using the 1200-SMB versus traditional GC–MS. Thus, the 1200-SMB lowers LOD, particularly for difficult analytes that are normally sacrificed in methods, and the detectability gains can amount to a few orders of magnitude over traditional GC–MS in real-world applications. [Copyright &y& Elsevier]

Low-pressure gas chromatography–mass spectrometry (LP-GC–MS) using a quadrupole MS instrument was further optimized and evaluated for the fast analysis of multiple pesticide residues in food crops. Performance of two different LP-GC–MS column configurations was compared in various experiments, including ruggedness tests with repeated injections of pesticides in matrix extracts. The tested column configurations employed the same 3m × 0.15mm i.d. restriction capillary at the inlet end, but different analytical columns attached to the vacuum: (A) a 10m × 0.53mm i.d., 1μm film thickness RTX-5 Sil MS column; and (B) a 10m × 0.25mm i.d., 0.25μm film thickness DB-5MS column. Under the optimized conditions (compromise between speed and sensitivity), the narrower analytical column with a thinner film provided slightly (<1.1-fold) faster analysis of <5.5min separation times and somewhat greater separation efficiency. However, lower detection limits for most of the tested pesticides in real extracts were achieved using the mega-bore configuration, which also provided significantly greater ruggedness of the analysis (long-term repeatability of analyte peak intensities, shapes, and retention times). Additionally, the effect of the increasing injection volume (1–5μl) on analyte signal-to-noise ratios was evaluated. For the majority of the tested analyte–matrix combinations, the increase in sensitivity caused by a larger injection did not translate in the same gain in analyte detectability. Considering the costs and benefits, the injection volume of 2–3μl was optimal for detectability of the majority of 57 selected pesticides in apple, carrot, lettuce, and wheat extracts. [Copyright &y& Elsevier]

Abstract: A rapid method using programmed temperature vaporiser injection–low-pressure gas chromatography–high-resolution time-of-flight mass spectrometry (PTV–LP-GC–HR-TOF-MS) for the analysis of multiple pesticide residues in fruit-based baby food was developed. The fast and inexpensive buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and “conventional” approach that employs ethyl acetate extraction followed by gel permeation chromatography (GPC) cleanup were employed for sample preparation. A PTV injector in solvent venting mode was used to reduce volume of acetonitrile and acetic acid (from the buffered QuEChERS extracts) that caused higher column bleed without their elimination. Otherwise, the time-to-digital converter would become saturated in HR-TOF-MS. For fast GC separation allowing analysis of 100 analytes within a 7min runtime, both a high temperature programming rate and vacuum conditions in a megabore GC column were employed. The use of HR-TOF-MS allowed the unbiased identification and reliable quantification of target analytes through the application of a narrow mass window (0.02Da) for extracting analyte ions and the availability of full spectral information even at very low levels. With only a few exceptions, the lowest calibration levels for the pesticides tested were ≤0.01mg/kg for both sample preparation methods, which meets the EU maximum residue limit set for pesticide residues in cereal-based foods and baby foods (2003/13/EC). [Copyright &y& Elsevier]

We developed a new instrumental approach, termed Supersonic GC–MS, which achieves fast, sensitive, confirmatory and quantitative analysis of a broad range of pesticides in complex agricultural matrices. Our Supersonic GC–MS system is a modification of a bench-top Agilent 6890 GC+5972 MSD with a supersonic molecular beam (SMB) interface and fly-through EI ion source. One of the main advantages of Supersonic GC–MS is an enhanced molecular ion (M+) in the resulting mass spectra. For example, The M+ was observed in all 88 pesticides that we studied using the Supersonic GC–MS whereas only 36 of 63 (57%) pesticides that we investigated in standard GC–MS exhibited a M+. We also found that the degree of matrix interference is exponentially reduced with the fragment mass by about 20-fold per 100 amu increasing mass. The enhancement of the M+ combined with the reduction in matrix background noise permit rapid full scan analysis of a potentially unlimited number of pesticides, unlike selected ion monitoring or MS–MS in which specific conditions are required in segments for targeted pesticides. Furthermore, unlike the case with chemical ionization, EI-SMB-MS spectra still give accurate identification of compounds using common mass spectral libraries. In practice, we found that libraries favor mass spectra in which the M+ appears, thus Supersonic GC–MS produced better spectra for compound identification than standard GC–MS. To achieve even lower identification limits, the M+ plus a second major ion (still using full scan data) gives higher signal-to-chemical noise ratios than the traditional 3-ion approach. The replacement of two low-mass ions with the M+ (supersonic two-ions method) results in a significant reduction of matrix interference by a factor of up to 90. Another main advantage of Supersonic GC–MS is its exceptional suitability for fast GC–MS with high carrier gas flow-rate. Fast Supersonic GC–MS was able to analyze thermally labile pesticides, such as carbamates, that are difficult or impossible to analyze in standard GC–MS. Large volume injection using a ChromatoProbe was also demonstrated, in the 6 min analysis of pesticides at 20 ng/g in a spice matrix. [Copyright &y& Elsevier]