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In the multiclass, multiresidue analysis of pesticides in food and environmental samples, pyrethroid insecticides are generally more difficult to analyze than other types of analytes. They do not ionize well by electrospray ionization, and although they are suitable for analysis by gas chromatography-mass spectrometry (GC-MS), selectivity using standard electron ionization (EI) in GC-MS is often insufficient because the molecular ion is rarely present. Many pyrethroids tend to have the same fragment ions in MS or high-resolution (HR)MS, and similar ion transitions in tandem MS/MS, leading to difficulties in distinguishing different pyrethroids from each other and chemical interferences in complex matrices. In this study, different forms of fast GC coupled with different types of MS detectors were compared for the analysis of up to 15 pyrethroids in barley extracts as a test case to assess which approach was the most advantageous. The three studied GC-MS techniques consisted of Cold EI using supersonic molecular beams in selected ion monitoring (SIM) mode with a single quadrupole instrument; triple quadrupole MS/MS; and HRMS using an orbital ion trap (orbitrap). A higher flow rate was used in Cold EI, and low pressure (LP) GC was employed in the MS/MS and orbitrap methods, to speed up the GC analyses (<10 min chromatograms in all cases). Each technique had some advantages over the others depending on specific pyrethroid analytes in the matrix. Nontargeted LPGC-orbitrap typically yielded the highest selectivity, but it rarely achieved the needed detectability to quantidentify the residues at 10 ng g -1 . Cold EI-SIM and LPGC-MS/MS usually met the needed detection limits and generally achieved similar capabilities for the targeted pyrethroids.

The goal of this study was to develop and validate a new method for simultaneous determination of 106 veterinary drugs and 227 pesticides and their metabolites plus 16 polychlorinated biphenyls (PCBs) at and below their regulatory levels established for catfish muscle in the European Union and U.S.A. To do this, two different QuEChERS-based methods for veterinary drugs and pesticides and PCBs were modified and merged into a single mega-method dubbed "QuEChERSER" (more than QuEChERS), which is presented here for the first time. The mega-method was validated in catfish at four different spiking levels with 10 replicates per level. Sample extraction of 2 g test portions was made with 10 mL of 4:1 (v/v) acetonitrile/water, and then an aliquot was taken for ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis of 106 veterinary drugs and 125 pesticides, including metabolites. The remaining extract after salting out was subjected to automated mini-solid-phase extraction cleanup (Instrument Top Sample Preparation) for immediate injection in low-pressure gas chromatography-tandem mass spectrometry (LPGC-MS/MS). The cleanup was conducted in parallel with the 10 min LPGC-MS/MS analysis for 167 PCBs, pesticides, and metabolites, which was conducted in parallel with the 10 min UHPLC-MS/MS analysis for 231 analytes to increase sample throughput (49 analytes were included in both techniques). In MS/MS, three ion transitions were monitored for nearly all targeted analytes to provide unambiguous identification as well as quantification. Satisfactory recoveries (70-120%) and relative standard deviations of ≤20% were achieved for 98 (92%) of the veterinary drugs and their metabolites and for 222 (91%) of pesticides, metabolites, and PCBs, demonstrating that the developed method is applicable for the analysis of these contaminants in fish as part of regulatory monitoring programs and other purposes.

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., (Copyright © 2019. Published by Elsevier B.V.)

Nitrites are added as a preservative to a variety of cured meats, including bacon, to kill bacteria, extend shelf life, and improve quality. During cooking, nitrites in the meat can be converted to carcinogenic nitrosamines (NAs), the formation of which is mitigated by the addition of antioxidants. In the past, the U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) monitored NAs in pan-fried bacon, but FSIS terminated monitoring of NAs in the 1990s due to the very low levels found. FSIS recently chose to conduct a risk assessment of NAs in cooked bacon to determine if current levels warrant routine monitoring of NAs again. To meet FSIS needs, we developed, validated, and implemented a new method of sample preparation and analysis to test cooked bacon for five NAs of most concern, which consist of N-nitroso-dimethylamine, -diethylamine, -dibutylamine, -piperidine, and -pyrrolidine. Sample preparation was based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) approach and analysis by gas chromatography-tandem mass spectrometry. Ruggedness was improved markedly in the analysis of the complex fatty extracts by backflushing the guard column, injection liner, and half of the analytical column after every injection. Validation results were acceptable with recoveries of 70-120% and <20% RSDs for the five NAs, with a reporting limit of 0.1 ng/g. NA concentrations in 48 samples were all <15 ng/g, with most <1 ng/g and many <0.1 ng/g. Also, microwave cooking of bacon gave slightly lower concentrations overall compared to pan-frying.

In this study, a residue analysis method for the simultaneous determination of 107 pesticides in traditional Chinese medicines (TCMs), Angelica sinensis, A. dahurica, Leonurus heterophyllus Sweet, Pogostemon cablin and Lonicera japonica Thunb., was developed using gas chromatography coupled with tandem mass spectrometry in negative chemical ionisation mode (GC-NCI-MS/MS). NCI has advantages of high sensitivity and selectivity to chemicals with electron-withdrawing groups, and yields low background interference. For sample preparation, QuEChERS (quick, easy, cheap, effective, rugged and safe) was applied. Due to the unique characteristics of TCMs, the clean-up step was optimised by adjusting amounts of primary secondary amine, C18, graphitised carbon black and silica sorbents. Validation was mainly performed by determining analyte recoveries at four different spiking concentrations of 10, 50, 100 and 200 ng g(-1), with seven replicates at each concentration. Method trueness, precision, linearity of calibration curves, lowest calibrated levels (LCLs) and matrix effects were determined to demonstrate method and instrument performance. Among the 107 pesticides tested, approximately 80% gave recoveries from 80% to 110% and < 10% relative standard deviation (RSD). The LCLs for nearly all pesticides were 5 ng g(-1), and as low as 0.1 ng g(-1) for dichlofenthion, endosulfan sulphate, flumetralin, isofenphos-methyl, methyl-pentachlorophenyl sulphide and trifluralin. The results indicate that GC-NCI-MS/MS is an excellent technique for quantitative and qualitative analysis of targeted GC-amenable pesticides at ultra-trace levels, especially in complex matrices such as TCMs.

A multi-class, multi-residue method for the analysis of 13 novel flame retardants, 18 representative pesticides, 14 polychlorinated biphenyl (PCB) congeners, 16 polycyclic aromatic hydrocarbons (PAHs), and 7 polybrominated diphenyl ether (PBDE) congeners in catfish muscle was developed and evaluated using fast low pressure gas chromatography triple quadrupole tandem mass spectrometry (LP-GC/MS-MS). The method was based on a QuEChERS (quick, easy, cheap, effective, rugged, safe) extraction with acetonitrile and dispersive solid-phase extraction (d-SPE) clean-up with zirconium-based sorbent prior to LP-GC/MS-MS analysis. The developed method was evaluated at 4 spiking levels and further validated by analysis of NIST Standard Reference Materials (SRMs) 1974B and 1947. Sample preparation for a batch of 10 homogenized samples took about 1h/analyst, and LP-GC/MS-MS analysis provided fast separation of multiple analytes within 9min achieving high throughput. With the use of isotopically labeled internal standards, recoveries of all but one analyte were between 70 and 120% with relative standard deviations less than 20% (n=5). The measured values for both SRMs agreed with certified/reference values (72-119% accuracy) for the majority of analytes. The detection limits were 0.1-0.5ng g(-1) for PCBs, 0.5-10ng g(-1) for PBDEs, 0.5-5ng g(-1) for select pesticides and PAHs and 1-10ng g(-1) for flame retardants. The developed method was successfully applied for analysis of catfish samples from the market., (Published by Elsevier B.V.)

Gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) serve as the most powerful analytical tools commonly used to monitor pesticide residues in food, among other applications. However, both GC-MS and LC-MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sample preparation, instrumentation, and operating conditions. Among the approaches that reduce matrix effects, the most common in pesticide residue applications is matrix-matched calibration because it is relatively inexpensive and simple. Also, it has been shown to work well during method validation when fortified samples are exactly matched with samples used for calibration. However, the quality of matrix-matched results in real-world analyses depends on the consistency of matrix effects among diverse samples. In this study, the variability of matrix effects was measured for 38 representative pesticides in 20 samples each (including different varieties) of rice, orange, apple, and spinach extracted using the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) method for analysis by LC-MS/MS and low-pressure GC-MS. Using LC-MS/MS, only oranges gave >20% matrix effects for a few pesticides. GC-MS exhibited larger matrix effects, but as in LC-MS/MS, the differences were reasonably consistent among the 20 samples tested. Main conclusions of this study are that for the conditions utilized: (1) matrix-matching was not needed for most pesticides in the simpler food matrices; and (2) for the more complex orange matrix, acceptably accurate quantitative results were achieved by using matrix-matching even with a different sample of the same type. However, full confidence cannot be extended to matrix-matched results, and for consequential applications such as regulatory enforcement, confirmatory analyses using alternate quantitative determinations should also be conducted., (Published by Elsevier B.V.)

Analytical methods for contaminant monitoring are generally targeted; i.e., they measure defined lists of compounds. Routine monitoring projects using targeted methods are not usually designed to screen for unrecognized or novel contaminants and therefore miss compounds within the region or population of study that cause, or have the potential to cause, adverse biological impacts. We describe a nontargeted analytical method utilizing direct sample introduction coupled to comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry. To test the capabilities of this instrumental method within the context of marine contaminant surveys, we characterized a broad array of nonpolar, persistent, and bioaccumulative contaminants in Atlantic common dolphin ( Delphinus delphis ) blubber, including compounds that are not typically monitored. Compound identifications were made by searching a standard reference database, by contemporaneously analyzing mass spectra from reference standards, and by de novo interpretation. We identified a total of 271 compounds belonging to 24 classes; all compounds but 1 were halogenated. Anthropogenic contaminants and halogenated natural products were concurrently detected. A total of 86 compounds were anthropogenic contaminants that are not routinely targeted in environmental surveys, and 54 compounds were halogenated natural products. A total of 112 spectra were identified de novo, demonstrating that exclusive reliance on commercially available reference standards and mass spectral libraries may miss a significant fraction of identifiable compounds. We also cataloged 27 halogenated mass spectra that were not able to be identified. Due to the volume and complexity of the identification data, we developed custom software to organize and provide shared access to the identified mass spectra and related information. The nontargeted analytical method and data reporting system, in combination with the analysis of a high-trophic-level sentinel species, demonstrates a framework for creating an inventory of persistent and bioaccumulative contaminants in marine environments, with the future goal of suggesting new compounds for further investigation by targeted monitoring and risk assessment.

We developed and evaluated a new method of low-pressure gas chromatography-tandem mass spectrometry (LP-GC/MS-MS) using a triple quadrupole instrument for fast analysis of 150 relevant pesticides in four representative fruits and vegetables. This LP-GC (vacuum outlet) approach entails coupling a 10 m, 0.53 mm i.d., 1 μm film analytical column between the MS transfer line and a 3 m, 0.15 mm i.d. capillary at the inlet. The MS creates a vacuum in the 10 m analytical column, which reduces the viscosity of the He carrier gas and thereby shifts the optimal flow rate to greater velocity. By taking advantage of the H(2)-like properties of He under vacuum, the short analytical column, a rapid oven temperature ramp rate, and the high selectivity and sensitivity of MS/MS, 150 pesticides were separated in <6.5 min. The 2.5 ms dwell time and 1 ms interscan delay of the MS/MS instrument were critical for achieving >8 data points across the 2-3 s wide peaks. To keep dwell and cycle times constant across all peaks, each segment consisted of 30 analytes (60 transitions). For assessment, we injected extracts of spiked broccoli, cantaloupe, lemon, and sweet potato from the updated QuEChERS sample preparation method. Average recoveries (n=72) were 70-120% for 144 of the pesticides, and reproducibilities were <20% RSD for all but 4 analytes. Also, detection limits were <5 ng/g for all but a few pesticides, depending on the matrix. In addition to high quality performance, the method gave excellent reliability and high sample throughput, including easy peak integration to obtain rapid results., (Published by Elsevier B.V.)

Quantitative method validation is a well-established process to demonstrate trueness and precision of the results with a given method. However, an assessment of qualitative results is also an important need to estimate selectivity and devise criteria for chemical identification when using the method, particularly for mass spectrometric analysis. For multianalyte analysis, automatic instrument software is commonly used to make initial qualitative identifications of the target analytes by comparison of their mass spectra against a database library. Especially at low residue levels in complex matrices, manual checking of results is typically needed to correct the peak assignments and integration errors, which is very time-consuming. Low-pressure gas chromatography-mass spectrometry (LP-GC-MS) has been demonstrated to increase the speed of analysis for GC-amenable residues in various foods and provide more advantages over the traditional GC-MS approach. LP-GC-MS on a time-of-flight (ToF) instrument was used, which provided high sample throughput with <10 min analysis time. The method had already been validated to be acceptable quantitatively for nearly 150 pesticides, and in this study of qualitative performance, 90 samples in total of strawberry, tomato, potato, orange, and lettuce extracts from the QuEChERS sample preparation approach were analyzed. The extracts were randomly spiked with different pesticides at different levels, both unknown to the analyst, in the different matrices. Automated software evaluation was compared with human assessments in terms of false-positive and -negative results. Among the 13590 possible permutations with 696 blind additions made, the automated software approach yielded 1.2% false presumptive positives with 23% false negatives, whereas the analyst achieved 0.8% false presumptive positives and 17% false negatives for the same analytical data files. False negatives frequently occurred due to challenges at the lowest concentrations, but 70% of them involved certain pesticides that degraded (e.g., captafol, folpet) or otherwise could not be detected. The false-negative rate was reduced to 5-10% if the problematic analytes were excluded. Despite its somewhat better performance in this study, the analyst approach was extremely time-consuming and would not be practical in high sample throughput applications for so many analytes in complicated matrices.

A higher monitoring rate is highly desirable in the labs, but this goal is typically limited by sample throughput. In this study, we sought to assess the real-world applicability of fast, low-pressure GC-time-of-flight MS (LP-GC/TOFMS) for the identification and quantification of 150 pesticides in tomato, strawberry, potato, orange, and lettuce samples. Buffered and unbuffered versions of QuEChERS (which stands for "quick, easy, cheap, effective, rugged, and safe") using dispersive solid-phase extraction (d-SPE) and disposable pipette extraction (DPX) for clean-up were compared for sample preparation. For clean-up of all sample types, a combination of 150 mg MgSO₄, 50mg primary secondary amine (PSA), 50 mg C₁₈, and 7.5 mg graphitized carbon black (GCB) per mL extract was used. No significant differences were observed in the results between the different sample preparation versions. QuEChERS took < 10 min per individual sample, or < 1 h for two chemists to prepare 32 pre-homogenized samples, and using LP-GC/TOFMS, < 10 min run time and < 15 min cycle time allowed > 32 injections in 8 h. Overall, > 126 analytes gave recoveries (3 spiking levels) in the range of 70-120% with < 20% RSD. The results indicate that LP-GC/TOFMS for GC-amenable analytes matches UHPLC-MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods., (Published by Elsevier B.V.)

The QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation method was modified to accommodate various cereal grain matrices (corn, oat, rice, and wheat) and provide good analytical results (recoveries in the range of 70-120% and RSDs <20%) for the majority of the target pesticides (about 180 analytes). The method consists of a 1 h shaking of a milled sample (2.5-5 g) in 20 mL of 1:1 (v/v) water/acetonitrile (or 25 mL of 1.5:1 water/acetonitrile in the case of rice) to provide simultaneous matrix swelling and analyte extraction. Then, a MgSO(4)/NaCl salt mixture (4:1, w/w) is added to the extract to induce phase separation and force the pesticides into the upper acetonitrile layer, a 1 mL aliquot of which is subsequently cleaned up using dispersive solid phase extraction with 150 mg of PSA, 50 mg of C(18), and 150 mg of MgSO(4). GC-amenable pesticides were analyzed using gas chromatography combined with time-of-flight mass spectrometry (GC-TOFMS) and the automated direct sample introduction technique for a large volume injection of the extracts. Ultraperformance liquid chromatography coupled to triple-quadrupole tandem mass spectrometry (UPLC-MS/MS) was employed for the analysis of LC-amenable pesticides. This method was implemented in a routine laboratory, providing about 3-fold increased sample throughput, 40-50% reduction in the cost of disposable materials and in the operation costs, 1:100 solvent waste reduction, and increased scope of the analysis versus the traditional approach based on the Luke method.

We successfully optimized an analytical method using gel permeation chromatography followed by direct sample introduction comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry to quantify multiple groups of targeted persistent organic pollutants and halogenated natural products (HNPs) simultaneously in fish oil samples. This new method has a wider analytical scope than the traditional approach to use multiple methods to cover each class of compounds. Our analysis revealed that the relatively more volatile and lighter organic compounds, such as polychlorinated biphenyls (PCBs), organochlorine pesticides, and other smaller organohalogen compounds, were still present in two brands of "PCB-free" cod liver oils, albeit at much lower levels than in an untreated commercial sample. Moreover, the less volatile organic compounds, such as polybrominated diphenyl ethers and brominated HNPs, were detected at similar levels in all three cod liver oils. This suggests that the commercial molecular distillation treatment used for removal of organic/inorganic toxic contaminants is only effective for the lighter organic contaminants.

An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GC x GC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GC x GC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2g of cod liver oil, which achieved limits of quantitation (LOQs) of 0.019-7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3',4,4',5-pentachloro biphenyl (CB126), which were sufficiently low for regulatory monitoring of 2g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil samples were achieved with good repeatability.

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 7 min 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 (0.02 Da) 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

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.

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-microL 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.

Automated large-volume direct sample introduction, or difficult matrix introduction (DMI), was investigated in the determination of 44 pesticide residues possessing a wide range of physico-chemical properties (volatility, polarity, pK(a)) in fruit-based baby food by means of gas chromatography-mass spectrometry (GC-MS) with a quadrupole mass analyzer. DMI has advantages over traditional injection because large volumes (up to 30 microL) of potentially dirty sample extracts can be injected into the GC-MS, but nonvolatile matrix components that would normally contaminate the inlet are removed after every injection. The extra matrix and glass surfaces involved in DMI, however, make the system more prone to the matrix-induced chromatographic enhancement effect, which adversely affects quantification of several pesticides. To overcome this problem, matrix-matched calibration standards and/or the use of analyte protectants were applied in the DMI approach, and the analysis of extracts was also compared before and after undergoing clean-up by dispersive solid-phase extraction. For best quantification, clean-up was still needed, and the combination of matrix-matching with analyte protectants gave the most reproducible results. Depending on the application, however, the addition of analyte protectants (a mixture of 3-ethoxy-1,2-propanediol, L-gulonic acid 3-lactone, and D-sorbitol) to sample extracts and calibration standards in solvent (non-matrix matched), gave satisfactory quantification for most of the 44 pesticides tested. The lowest calibration levels for 34 of the 44 pesticides were < or = 10 ng/g, which meets the standard required by the European Union Baby Food Directive (2003/13/EC).

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 3 m x 0.15 mm i.d. restriction capillary at the inlet end, but different analytical columns attached to the vacuum: (A) a 10 m x 0.53 mm i.d., 1 microm film thickness RTX-5 Sil MS column; and (B) a 10 m x 0.25 mm i.d., 0.25 microm 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 <5.5 min 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 (1-5 microl) 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 2-3 microl was optimal for detectability of the majority of 57 selected pesticides in apple, carrot, lettuce, and wheat extracts.

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.

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 thatlibraries 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.

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]