Benchtop GC-MS Research Articles

Evaluation of capillary microextraction of volatiles (CMV) coupled to a person-portable gas chromatograph mass spectrometer (GC–MS) for the analysis of gasoline residues

A novel dynamic headspace extraction device, the capillary microextraction of volatiles (CMV) was coupled to a person-portable GC–MS for the analysis of ignitable liquid residues (ILR) sampled from simulated fire debris. A benchtop GC–MS was used as a benchmark for the performance of the portable GC–MS. The use of a paper cup in conjunction with the CMV for in-field sampling of the VOCs associated with ILRs is presented for the first time. A five-minute sampling/extraction protocol was sufficient to recover six (6) analytes: toluene, ethylbenzene, m-xylene, o-xylene, 4-ethyltoluene, and 1,2,4-trimethylbenzene from a 0.01 µL spike of gasoline, with typical mass recoveries of 4–24 ng. Extractions from water-logged debris resulted in reliable detection of the same six compounds but up to 62% less was retained relative to dry debris. Recoveries for detected analytes ranged between 1 and 5% at several solution spike volumes suggesting proportional retention by the CMV. The CMV also demonstrated greater extraction capabilities than the portable GC–MS air sampling wand. Out of a 20-component mixture, 17 compounds were detected compared to the wand’s 13, with the majority of these at higher overall intensities for CMV. An overall 21-minute analytical method was developed using the CMV/Cup protocol capable of detecting several ILR-associated compounds at up to 10x greater sensitivity than traditional extraction techniques such as activated charcoal strips and SPME fibers.

Continuous vapor sampling of volatile organic compounds associated with explosives using capillary microextraction of volatiles (CMV) coupled to a portable GC–MS

The dynamic sampling and preconcentration device, capillary microextraction of volatiles (CMV), is coupled to a portable GC–MS for the rapid field detection of volatile organic compounds (VOCs) associated with explosives. The results of the portable GC–MS were compared to a benchtop GC–MS throughout this study. Sub-nanogram (ng) instrumental detection limits were achieved for each of the following analytes of interest (3-NT, 2,4-DNT, DPA, EC, DBP and 2-NDPA). Three different dynamic sampling methods were used with the CMV to sample and preconcentrate the volatiles prior to analysis. The headspace of a closed system was sampled over 10 min resulting in recoveries between 0.3 and 12%. Simulated open-air vapor sampling using a previously described vapor source resulted in an improvement of analyte recovery (ranging from 1.6 to 25%), for the same 10-minute sampling. A novel, continuous vapor delivery and sampling system was used, for the first time, to facilitate the delivery of sub-nanogram quantities of explosive analytes. The new continuous delivery system achieved significantly higher recoveries (3.0–89%) for all the analytes while requiring less sampling time (∼5 min) and sampling volumes than the other sampling techniques. The rapid sampling and preconcentration of sub-ng levels of VOCs in field scenarios was coupled to a ∼10-minute portable GC–MS method that compares favorably to the analytical figures of merit achieved by laboratory benchtop instruments and approximates the detection limits reported for canines.

Comparison of portable and benchtop GC–MS coupled to capillary microextraction of volatiles (CMV) for the extraction and analysis of ignitable liquid residues

A novel extraction device, capillary microextraction of volatiles (CMV) was coupled to a TRIDION-9 GC–MS with a needle trap (NTD) and evaluated for the analysis of ignitable liquids fire debris. The performance of the TRIDION-9 was compared to a benchtop GC–MS using CMV. A system detection limit of ~10 ng for each of 20 key ignitable liquid residue (ILR) compounds was determined for the T9 GC–MS. Dynamic headspace sampling of simulated ILRs was performed in closed and open-air systems. Closed system evaluations the CMV/NTD technique resulted in extraction performance similar to the CMV alone; however, ILR analysis on the T9 was impacted by limited chromatographic resolution. Compound identification was possible for 14 out of the 20 selected compounds on the T9 when 1 µL of a 1% standard accelerant mixture (SAM) was sampled, compared to 17 compounds on the benchtop GC–MS for the same mass loading. Open-air sampling with a modified vapor source resulted in the retention of most compounds with as low as 5 min. sampling, and equilibrium concentrations were reached after 10 min. No significant differences were observed between CMV and CMV/NTD sampling suggesting that the combined technique does not suffer from affinity bias. While the potential of the CMV/NTD extraction coupled to a T9 GC–MS for fire debris analysis was limited by the chromatographic resolution of the instrument, this study serves as proof of concept for the CMV’s potential for the extraction of ILRs in combination with portable GC–MS systems.

Overview of Forensic Toxicology, Yesterday, Today and in the Future.

The scope of forensic toxicology has been tremendously expanded over the past 50 years. From two general sections forensic toxicology can be further classified into 8-9 sections. The most outstanding improvement in forensic toxicology is the changes brought by instrumental development. The field of forensic toxicology was revolutionized by the development of immunoassay and benchtop GC-MS in the 1980's and LC-MS-MS in 2000's. Detection of trace amounts of analytes has allowed the use of new specimens such as hair and oral fluids, along with blood and urine. Over a longer period of time, continuous efforts have been made to efficiently extract and separate drug and poison from biological fluids. International endeavors to develop high quality standards and guidelines for drugs and poisons in biological specimens and to promote them in order to increase reliability of laboratories are also part of the recent advancement of forensic toxicology. Interpretation of postmortem toxicology encompasses various factors including postmortem redistribution and stability. Considering the recent trend, the interpretation of toxicological results should account for autopsy findings, crime scene information, and related medical history. The fields of forensic toxicology will continuously develop to improve analysis of target analytes from various specimens, quality assurance program, and results interpretation. In addition, the development of analytical techniques will also contribute further advancement of forensic toxicology. The societies of forensic toxicologists, such as TIAFT, will play an important role for the advancement of forensic toxicology by collaborating and sharing ideas between toxicologists from both developed and developing countries.

Field sampling demonstration of portable thermal desorption collection and analysis instrumentation

ABSTRACTThe HAPSITE® (Hazardous Air Pollutants on Site) is a portable gas chromatography-mass spectrometry (GC–MS) unit designed to aid air sampling technicians by identifying and quantifying volatile organic compounds from occupational and environmental sampling. The main goal of the present study was to extend prior laboratory-based work with the portable HAPSITE® ER (extended range model) thermal desorption (TD) capability to real-world field samples from both indoor and outdoor environments using different types of active and passive sampling mechanisms. Understanding the performance of the HAPSITE® ER in a realistic field setting will allow air quality sampling technicians to make improved decisions related to sampling and analysis methods in the field. An important finding was that certain charcoal-based TD sorbents were contraindicated for the HAPSITE® ER because of a substantial hydrocarbon bleed which degraded system performance. A novel time series TD sampler (Logistically Enabled Sampling System-Portable [LESS-P]) was validated using Tenax TA TD tubes against standard active sampling across multiple field sampling sites, and the qualitative analytical trends and compound identities were similar between LESS-P replicates analysed via benchtop GC–MS and HAPSITE® ER. Once validated, the LESS-P was used to determine the reference concentrations for passive sampling calculations. The results confirmed the passive sampling methodology within the benchtop system, but highlighted some systemic sensitivity limitations that must be addressed in order for the HAPSITE® to be accurately applied to passive sampling. We propose that the LESS-P time-series sampler may help to alleviate the requirement for sampling technicians to be on-site during active sampling, allowing for automated sampling throughout the duration of a sampling event.

Application of Receiver Operating Characteristic (ROC) Curves for Explosives Detection Using Different Sampling and Detection Techniques

Reported for the first time are receiver operating characteristic (ROC) curves constructed to describe the performance of a sorbent-coated disk, planar solid phase microextraction (PSPME) unit for non-contact sampling of a variety of volatiles. The PSPME is coupled to ion mobility spectrometers (IMSs) for the detection of volatile chemical markers associated with the presence of smokeless powders, model systems of explosives containing diphenylamine (DPA), 2,4-dinitrotoluene (2,4-DNT) and nitroglycerin (NG) as the target analytes. The performance of the PSPME-IMS was compared with the widely accepted solid-phase microextraction (SPME), coupled to a GC-MS. A set of optimized sampling conditions for different volume containers (1–45 L) with various sample amounts of explosives, were studied in replicates (n = 30) to determine the true positive rates (TPR) and false positive detection rates (FPR) for the different scenarios. These studies were obtained in order to construct the ROC curves for two IMS instruments (a bench-top and field-portable system) and a bench top GC-MS system in low and high clutter environments. Both static and dynamic PSPME sampling were studied in which 10–500 mg quantities of smokeless powders were detected within 10 min of static sampling and 1 min of dynamic sampling.

High-resolution mass spectrometry

High-resolution mass spectrometry (HRMS) using doublefocusing mass analyzers was established in chemistry laboratories in the 1960s. Coupled to a direct insertion probe or to gas chromatography, it revolutionized the elemental analysis of organic compounds. It also became a powerful tool in bioanalytical research providing high selectivity and specificity. However, modern benchtop GC–MS instruments cost significantly less and have been coupled to the faster scanning quadrupole or ion-trap mass analyzers, largely displacing GC–HRMS in most fields. Modern LC–MS instruments using electrospray ionization have many applications in bioanalytical laboratories and in “omics” research. Manufacturers, for arguably the first time, recognized a sizeable market for HRMS. In the past few years, robust GC–MS and, particularly, LC–MS equipment, mainly using time-of-flight or Fourier-transform mass-analyzer technology, are becoming increasingly affordable by many laboratories. This is also apparent from the remarkable increase in the number of publications. Therefore, the objective of this special volume is to give an overview of the current use of HRMS in the life sciences. Four review articles critically assess the use of HRMS in clinical and forensic toxicology, doping control, drug metabolism studies, food analysis, and the environmental sciences. This overview is followed by four original papers with new results from application of HRMS to drug screening, doping control, glycomics, and proteomics. We hope you find this special issue an invaluable source of information; it is intended for all readers with an interest in application of HRMS in clinical and forensic toxicology, doping control, drug metabolism, food analysis, environmental sciences, and proteomics and related fields. We thank all authors for submitting their interesting contributions for this special issue, the referees for their critical but constructive comments, and the editorial office and the editors for their friendly cooperation.

Profiling oestrogens and testosterone in human urine by stable isotope dilution/benchtop gas chromatography–mass spectrometry

Oestrogens, such as oestrone (E 1), 17β-oestradiol (E 2), oestriol (E 3) and their biologically active metabolites 2-methoxyoestrone (2-MeOE 1), 2-hydroxyoestradiol (2-OHE 2) 16-ketooestradiol (16-OE 2), 16-epioestriol (16-epiE 3), as well as testosterone (T) play an important role in physiological and pathological developmental processes during human development. We therefore aimed at developing an isotope dilution/bench top gas chromatography–mass spectrometry (ID/GC–MS) method, based on benchtop GC–MS, for the simultaneous determination (‘profiling’) of the above analytes in children. The method consisted of equilibration of urine (5 ml) with a cocktail containing stable isotope-labelled analogues of the analytes as internal standards ([2,4- 2H 2]E 1, [2,4,16,16- 2H 4]E 2, [2,4,17- 2H 3]E 3, [16,16,17- 2H 3]T, [1,4,16,16- 2H 4]2-MeOE 1, [1,4,16,16,17- 2H 5]2-OHE 2, [2,4,15,15,17- 2H 5]16-OE 2 and [2,4- 2H 2]16-epiE 3). Then, solid-phase extraction (C 18 cartridges), enzymatic hydrolysis (sulphatase from Helix pomatia (type H-1)), re-extraction, purification by anion exchange chromatography and derivatisation to trimethylsilyl ethers followed. The samples were analysed by GC–MS (Agilent GC 6890N/5975MSD; fused silica capillary column 25 m × 0.2 mm i.d., film 0.10 μm). Calibration plots were linear and showed excellent reproducibility with coefficients of determination ( r 2) between 0.999 and 1.000. Intra- and inter-assay coefficients of variation (CV) were <2.21% for all quantified metabolites. Sensitivity was highest for 2-OHE 2 (0.25 pg per absolute injection: signal-to-noise ratio (S/N) = 3) and lowest for 16-epiE 3 (2 pg per absolute injection: S/N = 2.6), translating into corresponding urine sample analyte concentrations of 0.025 ng ml −1 and 0.2 ng ml −1, respectively. Accuracy – determined in a two-level spike experiment – showed relative errors ranging between 0.15% for 16-OE 2 and 11.63% for 2-OHE 2. Chromatography showed clear peak shapes for the components analysed. In summary, we describe a practical, sensitive and specific ID/GC–MS assay capable of profiling the above-mentioned steroids in human urine from childhood onwards.

Determination of 11-deoxycortisol (Reichstein's compound S) in human plasma by clinical isotope dilution mass spectrometry using benchtop gas chromatography-mass selective detection.

A first assay based on stable isotope dilution/gas chromatography-mass spectrometry (ID/GC-MS) has been developed for plasma 11-deoxycortisol (Reichstein's compound S), the leading hormonal marker of 11beta-hydroxylase deficiency. A suitable internal standard being unavailable, we synthesized dideuterated 11-deoxycortisol according to a newly devised synthetic procedure. 17,21-Dihydroxy-pregna-1,4-diene-3,20-dione underwent selective deuteration using Wilkinson's catalyst. Our product [1alpha,2alpha-2H2]11-deoxycortisol was obtained in good yield (35.6%) and high isotopic purity (0.1% 2H0, 99.9% 2H2). Structural confirmation was done by MS and NMR. Our plasma work up consisted of equilibration of plasma with internal standard ([1alpha,2alpha-2H2]11-deoxycortisol), solid phase extraction with Extrelut NT columns, a clean up step using Sephadex LH-20 mini columns and preparation of heptafluorobutyrates as derivatives. Quantification was achieved by selected ion monitoring of m/z 465.40 (analyte) and m/z 467.40 (internal standard). One hundred twenty picograms of 11-deoxycortisol gave a signal to noise ratio of 10. Calibration plot was linear. Spiking experiments showed good accuracy with relative errors <3.0%. Intraassay precision CV was 4.78% and interassay precision CV was 4.56%. We succeeded in integrating our new analyte into our already existing multisteroid ID/GC-MS plasma assay, which now, in its expanded version, is capable of determining all major diagnostic steroids of androgen related disorders in a single profile: 11-deoxycortisol, 17alpha-hydroxyprogesterone, testosterone, 4-androstenedione, 17alpha-hydroxypregnenolone, dehydroepiandrosterone, androstanediol and 5alpha-dihydrotestosterone. The diagnostic potential of our multisteroid ID/GC-MS assay, the small amounts of plasma (0.5 ml) required, the rapid and convenient sample work up, the application of benchtop GC-MS instrumentation, and highest specificity offered by mass spectrometric detection prove our assay suitable for routine clinical use, especially in pediatric endocrinology.

Optimized determination of trace jet fuel volatile organic compounds in human blood using in-field liquid–liquid extraction with subsequent laboratory gas chromatographic–mass spectrometric analysis and on-column large-volume injection

A practical and sensitive method to assess volatile organic compounds (VOCs) from JP-8 jet fuel in human whole blood was developed by modifying previously established liquid–liquid extraction procedures, optimizing extraction times, solvent volume, specific sample processing techniques, and a new on-column large-volume injection method for GC–MS analysis. With the optimized methods, the extraction efficiency was improved by 4.3 to 20.1 times and the detection sensitivity increased up to 660 times over the standard method. Typical detection limits in the parts-per-trillion (ppt) level range were achieved for all monitored JP-8 constituents; this is sufficient for assessing human fuels exposures at trace environmental levels as well as occupational exposure levels. The sample extractions are performed in the field and only solvent extracts need to be shipped to the laboratory. The method is implemented with standard biological laboratory equipment and a modest bench-top GC–MS system.

Measuring Relative Reactivities of Electrophilic Aromatic Bromination Using a Benchtop GC-MS

This laboratory provides students with the opportunity to reinforce their knowledge of the numerous parameters involved in electrophilic aromatic substitution reactions. These concepts are investigated using a benchtop GC:MS. Students obtain hands-on experience with the coupling of gas-chromatographic analysis and mass-spectral analysis. Each student determines one data point by reacting a pair of compounds with bromine and iron (ID) chloride. Individual results are then pooled into composite class data, affording students more available information for analysis than is typical in an organic chemistry laboratory.

Fully-automated systematic toxicological analysis of drugs, poisons, and metabolites in whole blood, urine, and plasma by gas chromatography–full scan mass spectrometry

The availability of automated, rapid and reliable methods for the systematic toxicological analysis (STA) of drugs and poisons in biosamples is of great importance in clinical and forensic toxicology laboratories. Gas chromatography–continuous scan mass spectrometry (GC–MS) possesses a high potential in STA because of its selectivity and identification power. However, in order to develop a fully automated STA method based on GC–MS two main obstacles have to be overcome: (a) sample preparation is rather sophisticated owing to the need to isolate analytes from the aqueous matrix and to allow a correct GC repartition of polar analytes; (b) the large amount of information collected within a single analysis makes it difficult to isolate relevant analytical information (mass spectra of analytes) from the chemical noise. Using a bench-top GC–MS system equipped with a laboratory robot for sample preparation (the Hewlett-Packard 7686 PrepStation) and an original method for mass spectral purification, a fully automated STA procedure was developed involving isolation of drugs from the sample (whole blood with minimal pretreatment, plasma, urine) by means of solid-phase extraction, derivatization (trimethylsilylation) of the acidic–neutral and of the basic extracts, GC–MS analysis, processing of data, and reporting of results. Each step of the procedure, and the method for data analysis in particular, can be easily integrated with other existing STA methods based on GC–MS.

Evaluation of a benchtop ion trap gas chromatographic-tandem mass spectrometric instrument for the analysis of a model drug, tebufelone, in plasma using a stable-isotope internal standard

The performance of a benchtop GC-ion trap MS-MS instrument, the Varian Saturn 4D, was evaluated for the analysis of a model drug, tebufelone, in plasma. The sample preparation scheme was designed to provide a highly complex extract with matrix-derived interferences eluting near and at the retention time of tebufelone and its stable-isotope-labeled analog. The performance of the ion trap in the selected-reaction-monitoring mode was evaluated and also compared with results obtained on a benchtop GC-MS linear quadrupole instrument operated in the selected-ion-monitoring mode. The ion trap, operated in the selected-reaction-monitoring mode, was found to provide a higher degree of selectivity for the analysis of tebufelone. The increased selectivity obtained on the ion trap operated in the selected-reaction-monitoring mode resulted in superior accuracy and precision, as well as a lower limit of quantitation relative to that obtained by the GC-MS analysis. A linear standard curve was obtained over three orders of magnitude and the limit of quantitation for tebufelone in plasma was 100 pg/ml using the GC-ion trap MS-MS instrument.

Analysis of pesticide residues in food using gas chromatography—tandem mass spectrometry with a benchtop ion trap mass spectrometer

Recent developments on the Saturn GC—MS system offer enhanced capabilities for both the ion isolation and collision-induced dissociation steps in GC—MS—MS. With these improvements, benchtop GC—MS—MS can improve the detection limit of mass spectrometers for low-level target compounds in complex matrices. With this brief study of malathion, we demonstrate (1) excellent sensitivity, (2) wide dynamic range and (3) effective elimination of chemical background. GC—MS—MS is compared to standard (C—EI-Ms and GC—CI-MS technqiues for the analysis of malathion in orange extract. GC—MS—MS is the most selective and sensitive technique, virtually eliminating the background interference. Product ion mass spectra are invariant across the chromatographic peak and excellent linearity is observed over a range from 2.2 pg/μl to 2.2 ng/μl for malathion. Detection limit by GC—MS—MS was estimated at 0.5 μg/kg in the orange oil matrix ( S/N = 5).