Ion Monitoring Gas Chromatography-mass Spectrometry Research Articles

A gas chromatography–mass spectrometry method for the detection of chlorpyrifos contamination in palm‐based fatty acids

AbstractChlorpyrifos is a Malaysian Pesticide Board‐approved organophosphate insecticide, which may become concentrated during fractionation. The objective of this project was to develop and validate a method to detect and quantify chlorpyrifos in food‐grade fatty acids ingredients, e.g. caprylic‐capric acid mixture and oleic acid (OLA) used to synthesize triacylglyceride based food additives and in the cosmetic industry. A selective ion monitoring gas chromatography–mass spectrometry method with a matrix‐matched calibration curve calibration was selected. The method involved the direct injection of chlorpyrifos spiked into the fatty acids matrix. The percentage recoveries at spiking levels of 0.5, 0.75, 2.5, and 4.0 μg g−1 of chlorpyrifos in OLA and caprylic‐capric acid ranged from 85.7%–101.1% to 97.2%–112%, respectively, with a relative standard deviation of within 11%. The intra‐day and inter‐day precision were deemed acceptable as indicated by an relative SD value of within 10%. A good linear relationship with a coefficient of correlation >0.99 for the matrix‐matched calibration was achieved between 0.5 and 5 μg g−1. The limit of detection and limit of quantification corresponded to 0.5 μg g−1 for OLA and 0.55 μg g−1 for caprylic‐capric acid.

Molecular analysis of black coatings and anointing fluids from ancient Egyptian coffins, mummy cases, and funerary objects

Black organic coatings and ritual deposits on ancient Egyptian coffins and cartonnage cases are important and understudied sources of evidence about the rituals of funerary practice. Sometimes, the coatings were applied extensively over the surface of the coffin, resembling paint; in other cases, they were poured over the mummy case or wrapped body, presumably as part of a funerary ritual. For this study, multiple samples of black coatings and ritual liquids were taken from 20 Egyptian funerary items dating to a specific time period (c. 943 to 716 BC). Multiple sampling from each object enabled several comparisons to be made: the variability of the black coating within one application, the variability between two applications on one object, and the variability from object to object. All samples were analyzed for lipids using gas chromatography-mass spectrometry (GC-MS), and 51 samples from across the 20 items were further analyzed for the presence of bitumen using solid phase separation followed by selected ion monitoring GC-MS. The majority of the black substances were found to comprise a complex mixture of organic materials, including bitumen from the Dead Sea, conifer resin, and Pistacia resin, providing evidence for a continuation in international trade between Egypt and the eastern Mediterranean after the Late Bronze Age. Both the coating and the anointing liquid are very similar to mummification balms, pointing to parallels with Egyptian embalming rituals and raising questions about the practical aspects of Egyptian funerary practice.

Solid-phase extraction and gas chromatography-mass spectrometry analysis of 11-nor-9-carboxy-δ9-tetrahydrocannabinol in urine for monitoring marijuana abuse

A specimen pretreatment procedure, combining solid-phase extraction and methylation, was developed for the analysis of 11-nor-9-carboxy-Δ9- tetrahydrocannabinol (9-THC-COOH) in urine for monitoring marijuana exposure. d3-11-Nor-9-carboxy-Δ9-tetrahydrocannabinol (d3-9-THC-COOH) was used as an internal standard, while the now universal selected ion monitoring gas chromatography-mass spectrometry approach was used for detection (m/z 313, 357, 372 and 316, 360, 375 for 9-THC-COOH and d3-9-THC-COOH, respectively) and quantitation (m/z 372 and 375 for 9-THC-COOH and d3-9-THC-COOH, respectively). The effectiveness of the overall procedure was evaluated. One of the extraction columns evaluated achieved > 90% recovery of the analyte in 5-mL drug-free urine fortified with 15 ng/mL 9-THC-COOH. Using the one-point calibration approach, the overall protocol achieved the following analytical parameters: detection limit: 2.09 ng/mL; limit of quantitation: 4.18 ng/mL; upper end of linear range: 376 ng/mL (or better); interday precision: 1.49- 8.03% CV in the 4.18-376 ng/mL concentration range studied.

Urushiol Compounds Detected in Toxicodendron-Labeled Consumer Products Using Mass Spectrometry

Urushiol, the culprit allergen in Toxicodendron plants such as poison ivy, is an oily mixture of 15 and 17 carbon side chain alk-(en)-yl catechols. Recently, consumer products have been identified that contain Toxicodendron as an ingredient on their label; however, no studies have assessed whether urushiol is indeed present within these products. The aim of the study was to determine whether urushiol compounds are present in consumer products labeled as containing Toxicodendron species. Gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry were performed on 9 consumer products labeled as containing Toxicodendron species, including topical homeopathic remedies. Single ion monitoring gas chromatography-mass spectrometry was programmed in selective ion mode to detect 3-methylcatechol characteristic fragment ions of alk-(en)-yl catechols after silanization. Similarly, single ion monitoring liquid chromatography-tandem mass spectrometry was programmed to detect 4 urushiol pentadecylcatechols and 5 urushiol heptadecylcatechols using previously reported mass-to-charge ratios. Gas chromatography-mass spectrometry detected alk-(en)-yl catechols in 67% (6/9) of the products tested. Liquid chromatography-tandem mass spectrometry detected multiple urushiol pentadecylcatechols and heptadecylcatechols in 44% (4/9) of the products tested. Alk-(en)-yl catechols and multiple urushiols were detected in consumer products listing Toxicodendron species as an ingredient. Clinicians should be aware of these known allergenic ingredients in consumer products.

Identification of potential indicators of time-dependent tequila maturation and their determination by selected ion monitoring gas chromatography–mass spectrometry, using salting-out liquid–liquid extraction

In this work, gas chromatography–mass spectrometry (GC–MS) profiles obtained for a series of rested and aged tequilas were statistically compared to identify volatile compounds indicative of time-dependent tequila maturation. For the determination of nine selected compounds, 2-acetylthiazole was added as internal standard, ethyl acetate extraction was carried out in the presence of sodium chloride (salting-out) and sodium sulfate was used to eliminate water traces. Baseline separation was achieved within 18 min and quantification was carried out by selected ion monitoring. The method detection limits were as follows: 2.10 µg L− 1 guaiacol (m/z 109), 1.78 µg L− 1 4-methylguaiacol (m/z 123), 1.97 µg L− 1 4-ethylguaiacol (m/z 137), 3.78 µg L− 1trans-whiskey lactone (m/z 99), 4.42 µg L− 1cis-whiskey lactone (m/z 99), 10.3 µg L− 1eugenol (m/z 103), 8.27 µg L− 1 vanillin (m/z 151), 14.2 µg L− 1 apocynin (m/z 151), 12.1 µg L− 1 syringaldehyde (m/z 182). For accuracy testing, 100 µg L− 1 of each analyte was added to silver tequila, yielding the recoveries in the range 92.1–116%. Data obtained in the analysis of 28 tequilas confirmed that the concentrations of individual compounds were changing among liquors at different maturation stage; however, due to many variables affecting the profile of volatile/semi-volatile compounds during aging in wooden barrels, discrimination of tequilas was not feasible. Otherwise, the proposed procedure allows for reliable determination of nine odor-active compounds in tequila at trace levels with simple sample pretreatment and short analytical run.

Application of Selected Ion Monitoring-Gas Chromatography Mass Spectrometry (SIM-GCMS) for Quantification of Poly Aromatic Hydro Carbons in Surface Water from Sarawak, Mambong River (Malaysia)

Background: Increasing activities have led to serious environmental problems due to Pullution caused by toxic materials such as poly aromatic carbons whose levels are rising in the environment.
 Objective: The study presented here carried out the ultra-trace Quantification of Poly Aromatic Hydro carbons in surface water using Selected Ion Monitoring with optimization Gas Chromatography Mass Spectrometry parameter.
 Methods: A Shimadzu QP 2010 Plus GCMS equipped with an auto-injector AOC-20i, 30 m x 0.25 mm x 0.25 um of BP-X5 capillary column (SGE, USA) was used to obtain the result of poly aromatic hydrocarbons to separate and quantify the PAH compounds as well as to identify the Polyromantic Hydrocarbon using USEPA.
 Results: The amount of polycyclic aromatic hydrocarbons (PAHs) at ultra-trace level in the surface water samples was estimated. Sixteen Poly Aromatic Hydro carbons were identified among which Naphthalene Pyrene (45.7 ng/L), Chrysene (59.38 ng/L), Benzo (g, h, i) perylene (40.35 ng/L) as the major pollutants in the water surface of Mambong River water. Total Poly Aromatic Hydro carbons (PAHs) concentrations ranged from 2.0 to 40 ng L-1 was detected in the river water.
 Conclusion: The Selected Ion Monitoring -Gas Chromatography Mass Spectrometry (SIM-GCMS) can be considered as sensitive and robust method to analyse PAHs contamination in environmental samples. Thus, help the researchers to uncover the critical areas of environmental pollution at ultra-trace level that many researchers were not able to explore.

Chemical communication during foraging in the harvesting ants Messor pergandei and Messor andrei

We combined behavioral analyses in the laboratory and field to investigate chemical communication in the formation of foraging columns in two Nearctic seed harvesting ants, Messor pergandei and Messor andrei. We demonstrate that both species use poison gland secretions to lay recruitment trails. In M. pergandei, the recruitment effect of the poison gland is enhanced by adding pygidial gland secretions. The poison glands of both species contain 1-phenyl ethanol. Minute quantities (3μl of a 0.1ppm solution) of 1-phenyl ethanol drawn out along a 40cm long trail released trail following behavior in M. pergandei, while M. andrei required higher concentrations (0.5-1ppm). Messor pergandei workers showed weak trail following to 5ppm trails of the pyrazines 2,5-dimethylpyrazine and 2,3,5-trimethylpyrazine, whereas M. andrei workers showed no behavioral response. Minute quantities of pyrazines were detected in M. pergandei but not in M. andrei poison glands using single ion monitoring gas chromatography-mass spectrometry.

Estimating naphthenic acids concentrations in laboratory-exposed fish and in fish from the wild

Naphthenic acids (NAs) are the most water-soluble organic components found in the Athabasca oil sands in Alberta, Canada, and these acids are released into aqueous tailing waters as a result of bitumen extraction. Although the toxicity of NAs to fish is well known, there has been no method available to estimate NAs concentrations in fish. This paper describes a newly developed analytical method using single ion monitoring gas chromatography–mass spectrometry (GC–MS) to measure NAs in fish, down to concentrations of ∼0.1 mg kg −1 of fish flesh. This method was used to measure the uptake and depuration of commercial NAs in laboratory experiments. Exposure of rainbow trout ( Oncorhynchus mykiss) to 3 mg NAs l −1 for 9 d gave a bioconcentration factor of ∼2 at pH 8.2. Within 1 d after the fish were transferred to NAs-free water, about 95% of the NAs were depurated. In addition, the analytical method was used to determine if NAs were present in four species of wild fish – northern pike ( Esox lucius), lake whitefish ( Coregonus clupeaformis), white sucker ( Catostomus commersoni), walleye ( Sander vitreus) – collected from near the oil sands. Flesh samples from 23 wild fish were analyzed, and 18 of these had no detectable NAs. Four fish (one of each species) contained NAs at concentrations from 0.2 to 2.8 mg kg −1. The GC–MS results from one wild fish presented a unique problem. However, with additional work it was concluded that the NAs concentration in this fish was <0.1 mg kg −1.

4-Hydroxy-2-alkenals in polyunsaturated fatty acids-fortified infant formulas and other commercial food products

4-Hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) were determined using selected ion-monitoring gas chromatography-mass spectrometry (GC-MS) in 56 kinds of commercially available PUFA-fortified foods including infant formulas and baby foods. HHE and HNE, each specifically coming from the oxidation of n-3 and n-6 polyunsaturated fatty acids (PUFA), were observed at <10–77 and 41–132 µg kg–1 in the infant formulas (n = 12) and at <10–52 and 36–116 µg kg–1 in the baby foods (n = 7), respectively. 4-Hydroxy-2-alkenals in infant formulas and baby foods were further determined at 10 and 30 days after opening in an attempt to examine the time dependence of the levels of 4-hydroxy-2-alkenals. The values of HHE and HNE had increased appreciably to <10–220 and 79–792 µg kg–1 in infant formulas and to <10–112 and 135–572 µg kg–1 in baby foods, respectively, at 10 days and decreased, although statistically not significant, in most of the tested samples after 30 days, which suggested that the reactive compounds might interact with other constituents like proteins in the samples to form adducts or be decomposed with time. Based on the current study, it was calculated that 3-month to 1-year-old babies maintained exclusively on these commercially available PUFA-fortified infant formulas or baby foods could be exposed to a maximum of 20.2 µg kg–1 body weight day–1 of 4-hydroxy-2-alkenals, which is two orders of magnitude higher than the exposure of Korean adults estimated in a previous study of the authors’ (2005). The present study may trigger future studies investigating the physiological influence of 4-hydroxy-2-alkenals originating from the diet on man at an early stage of development.

Sensitive profiling of chemically diverse bioactive lipids

Here, we present an improved method for sensitive profiling of lipids in a single high-performance liquid chromatography-electrospray ionization-quadrupole time of flight mass spectrometry experiment. The approach consists of i) sensitive isocratic elution, which takes advantage of C18 column material that is resistant to increased pH values induced by piperidine, ii) chemometric alignment of mass spectra followed by differential analysis of ion intensities, and iii) semiquantitative analysis of extracted ion chromatograms of interest. A key advantage of this method is its wide applicability to extracts that harbor lipids of considerable chemical complexity. The method allows qualitative and semiquantitative analysis of fatty acyls, glycerophospholipids (such as glycerophosphatidylinositols, glycerophosphatidylserines, and glycerophosphatidylcholines in brain extracts), phosphatidylinositol mannosides, acylated glycerophospholipids, sphingolipids (including ceramides and gangliosides in brain extracts), and, for the first time with ESI, prenols and mycolic acids (MAs). MAs are targets in antimycobacterial therapy, and they play an important immunomodulatory role during host-pathogen interactions. We compared high-resolution mass spectra of MAs derived from Mycobacterium bovis Bacille Camette-Guérin during entry into nonreplicative conditions induced by oxygen deprivation (hypoxic dormancy). Although the overall composition is not drastically altered, there are pronounced differences in individual MAs. alpha-MAs accumulate during entry into dormancy, whereas a subpopulation of keto-MAs is almost entirely eliminated. This effect is reversed upon resuscitation of dormant mycobacteria. These results provide detailed chemical information with relevance to drug development and immunobiology of mycobacteria.

Tissue Distribution of Quetiapine in 20 Cases in Virginia

Quetiapine fumarate (Seroquel) is a dibenzothiazepine psychotropic agent that was introduced in 1997 for treating psychoses. Quetiapine is being found with increasing frequency in postmortem cases in Virginia. We report the postmortem results and histories of 20 quetiapine cases from the Office of the Chief Medical Examiner in Virginia covering the period 1999 through 2004. Quetiapine was extracted from blood using a basic drug solid-phase extraction (SPE) and identified by full scan electron impact gas chromatography-mass spectrometry (GC-MS). Quetiapine quantification was accomplished by forming the trimethylsilyl derivative with bis(trimethylsilyl)trifluoracetamide/trimethylchlorosilane and using selected ion monitoring GC-MS. The quetiapine trimethylsilyl derivative ions acquired were m/z 210, 239, and 322. Methapyrilene was the internal standard, and ions m/z 97 and 58 were monitored. The method was linear from 0.1 to 5.0 mg/L with a limit of quantitation of 0.1 mg/L. The quetiapine mean and range of concentrations found in each tissue are as follows: peripheral blood, 7.7 mg/L (0.14-37 mg/L, n = 17); heart blood, 23.63 mg/L (0.53-76 mg/L, n = 4); liver, 91 mg/Kg (1.1-510 mg/Kg, n = 19); bile, 44 mg/L (6.0-96 mg/L, n = 4); urine, 15 mg/L (1.9-37 mg/L, n = 8); gastric, 897 mg total (3.5-3960 mg, n = 7); and vitreous, 1.4 mg/L (0.2-3.2 mg/L, n = 5). The average of all blood concentrations in 18 cases in which quetiapine contributed to the cause of death was 7.95 mg/L (0.4-76 mg/L). The manner of death in 13 of those cases was suicide, two were undetermined, and three were accidents. In two cases in which quetiapine was an incidental finding, the blood concentrations were 0.14 and 1.0 mg/L. Quetiapine and other toxicological findings are presented with the cause and manner of death to assist in interpreting future quetiapine findings in postmortem samples.

The N-Acetyl-D-glucosaminylphosphatidylinositol De-N-acetylase of Glycosylphosphatidylinositol Biosynthesis Is a Zinc Metalloenzyme

The de-N-acetylation of N-acetyl-D-glucosaminylphosphatidylinositol (GlcNAc-PI) is the second step of mammalian and trypanosomal glycosylphosphatidylinositol biosynthesis. Glycosylphosphatidylinositol biosynthesis is essential for Trypanosoma brucei, the causative agent of African sleeping sickness, and GlcNAc-PI de-N-acetylase has previously been validated as a drug target. Inhibition of the trypanosome cell-free system and recombinant rat GlcNAc-PI de-N-acetylase by divalent metal cation chelators demonstrates that a tightly bound divalent metal cation is essential for activity. Reconstitution of metal-free GlcNAc-PI de-N-acetylase with divalent metal cations restores activity in the order Zn(2+) > Cu(2+) > Ni(2+) > Co(2+) > Mg(2+). Site-directed mutagenesis and homology modeling were used to identify active site residues and postulate a mechanism of action. The characterization of GlcNAc-PI de-N-acetylase as a zinc metalloenzyme will facilitate the rational design of anti-protozoan parasite drugs.

A robust and selective method for the quantification of glycosylphosphatidylinositols in biological samples.

We have developed an assay for the quantification of glycosylphosphatidylinositol (GPI)-anchored glycoconjugates. The method is based on nitrous acid deamination and sodium borodeuteride reduction of the glucosamine residue, common to all GPI structures, to yield [1-2H]-2,5-anhydromannitol. Following acid methanolysis and trimethylsilyl derivatization, detection is by selected ion monitoring gas chromatography-mass spectrometry. The unnatural inositol isomer scyllo-inositol is used as an internal standard and the [1-2H]-2,5-anhydromannitol trimethylsilyl derivative is detected by following a characteristic electron-impact fragment ion at m/z 273. This method is more selective for GPIs than assays based on measuring myo-inositol content, which are often confounded by contaminating inositol-phospholipids. We show that the method can be applied to measure total GPI content in crude total lipid extracts and even in whole trypanosome ghosts. The method was applied to whole cell lysates of wild-type, GPI-deficient, and glycosaminoglycan-deficient CHO cells. The data revealed that proteoglycans did not interfere with total glucosamine estimates but that there are background levels of non-GPI and nonproteoglycan glucosamine-containing material in CHO cells.

Clinical spectrum of succinic semialdehyde dehydrogenase deficiency.

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder affecting CNS gamma-aminobutyric acid (GABA) degradation. SSADH, in conjunction with GABA transaminase, converts GABA to succinate. In the absence of SSADH, GABA is converted to 4-OH-butyrate. The presence of 4-OH-butyrate, a highly volatile compound, may be undetected on routine organic acid analysis. Urine organic acid testing was modified at the authors' institution in 1999 to screen for the excretion of 4-OH-butyrate by selective ion monitoring gas chromatography-mass spectrometry in addition to total ion chromatography. Since then, five patients with 4-hydroxybutyric aciduria have been identified. The authors add the clinical, neuroimaging, and EEG findings from a new cohort of patients to 51 patients reported in the literature with clinical details. Ages ranged from 1 to 21 years at diagnosis. Clinical findings include mild-moderate mental retardation, disproportionate language dysfunction, hypotonia, hyporeflexia, autistic behaviors, seizures, and hallucinations. Brain MRI performed in five patients at the authors' institution revealed symmetric increased T2 signal in the globus pallidi. SSADH deficiency is an under-recognized, potentially manageable neurometabolic disorder. Urine organic acid analysis should include a sensitive method for the detection of 4-hydroxybutyrate and should be obtained from patients with mental retardation or neuropsychiatric disturbance of unknown etiology.

Effects of Culture Conditions on the Mycolic Acid Composition of Isolates of Rhodococcus spp. from Activated SludgeFoams

The influence of two different carbon sources and three incubation temperatures on the mycolic acid compositions of three Rhodococcus isolates from activated sludge was examined using Selective Ion Monitoring (SIM) gas chromatography-mass spectrometry (GC-MS). Considerable qualitative and quantitative differences were detected in the mycolic acid compositions of the three very closely related isolates grown under the same conditions. Culture age also affected both the chain lengths and proportions of saturated mycolic acids detected in cell extracts, but not in the same manner for each isolate. Mycolic acids generally were of shorter chain lengths in cells grown with Tween 80 compared to glucose grown cells in strain 11R but the opposite situation occurred with strains A7 and D5. In all three, the proportion of unsaturated mycolic acids decreased with increasing growth temperatures. The taxonomic relevance of these observations and possible explanations for the observed changes in mycolic acid composition under various culture conditions are discussed.

Isotopic analogues as internal standards for quantitative analyses of drugs and metabolites by GC-MS--nonlinear calibration approaches.

In order to achieve accurate quantitation of drugs and metabolites (analytes) in complex matrices, 2H- (and less commonly 13C-) labeled analogues of the analytes are now routinely adapted as the internal standards (IS) using linear calibration models to fit data generated by selected ion monitoring gas chromatography-mass spectrometry (GC-MS) protocols. In this study, the effects of cross-contribution (contribution of the IS to the intensity of the ion designated for the analyte and vice versa) on the linearity of the calibration data are examined. Nonlinear approaches that may address this problem are also studied. Two ion pairs (one with least and one with significant cross-contribution) from each of the following analyte/IS pairs are used as the exemplar systems for this study: butalbital/13C4-butalbital, butalbital/2H5-butalbital, secobarbital/13C4-secobarbital, and secobarbital/2H5-secobarbital. Analyte/IS ion intensity ratios of a series of standard solutions are correlated with the analyte/IS concentration ratios using one-point, multiple-point (unweighted and weighted) linear, and hyperbolic functions. The one-point calibration approach produces excellent calibration results in treating data derived from ion pairs with no significant cross contribution. In cases where significant cross-contribution exists, results derived from the one-point approach show, as expected, significant deviations at both ends of the concentration range. With the cross-contribution phenomenon accounted for, the hyperbolic calibration model is clearly more effective in fitting calibration data at both the lower and higher analyte concentration ends, thus significantly lowering the detection limit and extending the calibration range to a higher level. However, the calibration range cannot be extended indefinitely. At the low concentration end, noise-to-signal ratio and the cross-contribution of the IS to the intensity of the ion designated for the analyte, however insignificant, will incrementally reduce the quality of the observed ion intensity and intensity ratio data. At the high concentration end, detection saturation and the cross-contribution of the analyte to the intensity of the ion designated for the IS, however insignificant, will incrementally decrease the "slope" of the calibration curve. Thus, acceptable sensitivity (increase in analyte/IS ion-pair intensity ratio per unit increase in analyte concentration) of the calibration curve will become the limiting factor.

Quantitation of flavor-related alkenylbenzenes in tobacco smoke particulate by selected ion monitoring gas chromatography-mass spectrometry.

Little is known about the possible health effects associated with inhaling alkenylbenzenes through cigarette smoking, even though these flavor-related compounds have known toxic effects in animals. We developed a rapid and sensitive solid-phase extraction (SPE) method to quantify seven alkenylbenzenes and piperonal in mainstream cigarette smoke particulate. The smoke particulate fraction of a single cigarette was collected on Cambridge filter pads, solvent extracted, concentrated, purified with SPE, and analyzed by selected ion monitoring gas chromatography-mass spectrometry. We positively identified and quantified five alkenylbenzenes compounds (eugenol, isoeugenol, methyleugenol myristicin, and elemicin) and piperonal in the smoke particulate from eight U.S. brands with mean levels (measured in triplicate) ranging from 6.6 to 4210 ng per cigarette. Additionally, complete blocking of nearly invisible ventilation holes in the cigarette filter increased 2- to 7-fold the percent transfer of alkenylbenzenes from tobacco to the particulate fraction of mainstream smoke.

Solid phase microextraction of alkenylbenzenes and other flavor-related compounds from tobacco for analysis by selected ion monitoring gas chromatography–mass spectrometry

Some constituents found in natural flavorings are known to exhibit toxic properties. We developed a rapid method for quantifying 12 flavor-related compounds in cigarette tobacco using headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. Using selected ion monitoring, we quantified and positively identified coumarin; pulegone; piperonal and nine alkenylbenzenes, including trans-anethole, safrole, methyleugenol and myristicin in one or more brands of cigarettes. In 62% of 68 brands analyzed, we detected one or more of the flavor-related compounds ranging from 0.0018 to 43 μg/g. Toxic properties of these flavor-related compounds may constitute an additional health risk related to cigarette smoking.

Analysis of the structural diversity of mycolic acids of Rhodococcus and Gordonla isolates from activated sludge foams by selective ion monitoring gas chromatography–mass spectrometry (SIM GC–MS)

A method using Selective Ion Monitoring (SIM) gas chromatography–mass spectrometry is described for analysis of mycolic acids which reveals a hitherto unrecognised chemical structural diversity among these in some members of the Mycolata. The structural interpretation of mass spectral data of mycolic acids from Rhodococcus spp and Gordonla spp using SIM is discussed.

Detection of residues using multivariate modelling of low-level GC-MS measurements

The chemometric analysis of low-level analytical data is hampered by the common presence of interfering compounds, by the frequent absence of measurement signals and by a non-constant measurement variability which is related to concentration level in a non-linear way. A model is presented to handle this type of data in the context of the practical problem of multivariate detection from gas chromatography/mass spectrometry (GC-MS) data. The model, based on log ratio modelling, is compared with previous approaches to parts of the problem. The basic idea behind the model is to define for the multivariate detection problem a null hypothesis for the values of log ratio measurements and to estimate variability as a function of total measured intensity. In practice it is often impossible to anticipate all kinds of interference which may occur. Therefore we propose to use expert assessments of the probability that certain expected peak ratios are generated by the analyte rather than by interferences. These expert assessments can then be used to define a proper null hypothesis for the multivariate detection test. The application of the model is illustrated for the detection of the illegal growth promoter clenbuterol in urine by selected ion-monitoring GC-MS.