Gas Chromatography-mass Selective Detection Research Articles

Solid-Phase Microextraction--Gas Chromatographic--Mass Selective Detection Analysis of Selected Sources of Menthol

Manual solid-phase microextraction (SPME) coupled with gas chromatography-mass selective detection has been shown to be a rapid, precise, and reliable method for testing the origin and purity of menthol samples. Exposure of a 65-μm carboxenpolydimethylsiloxane fiber to the headspace above a menthol sample held at 50°C in a sealed vial provides for excellent signal-to-noise responses for a variety of volatile components. Detection differences in menthol compositions are based on documenting predictable changes in the ratios of identified and/or unknown components adsorbed onto the SPME fiber. Differences in composition can be detected as a function of manufacturing site using this approach. In addition, the presence of added synthetic menthol can be detected in the natural samples employing the same principle, thus assisting in determining the purity of the natural menthol.

Urinary excretion of diethylstilbestrol in the ostrich.

Stilboestrol tablets (20 x 1 mg) were given to 4 ostriches. Urine was collected over a period of 8 days and stored frozen at-20 degrees C pending analysis. Analyses were performed on a gas chromatograph-mass selective detector for the presence of parent compound and/or metabolites. Diethylstilbestrol and its metabolite, dienestrol, were detected in urine; dienestrol only for 1 day but diethylstilbestrol for 8 days after administration. Residue analysis for the use of diethylstilbestrol as growth promoter can be performed on the urine of ostriches by scanning for parent compound only since it can be detected longer than the metabolite.

Validation of [13C]urea breath test for Helicobacter pylori using a simple gas chromatograph-mass selective detector.

Isotope ratio mass spectrometry (IRMS) is the accepted method for accurately measuring the 13CO2:12CO2 ratio in the non-invasive and non-radioactive [13C]urea breath test (13C-UBT) for Helicobactor pylori. The IRMS instrument, an expensive and highly specialized analyser, is rarely available. The objective of this project was to modify and validate the use of a simple bench-top gas chromatograph-mass selective detector (GC-MSD) for 13C-UBT. Breath samples from 71 patients were taken at baseline and 30 min after ingestion of 100 mg [13C]urea. The breath samples were analysed using GC-MSD in the selected ion monitoring mode. The reference 13CO2:12CO2 ratio was from NBS19 obtained from the US National Institute of Standards and Technology. 13CO2:12CO2 ratios of the breath samples were determined. Excess delta per thousand (per mil, delta/thousand) of the 30 min sample over the baseline (deltadelta/thousand) of > or = 6deltadelta/thousand was considered H. pylori positive. Results from 13C-UBT and histology determined blind to each other were compared. The coefficient of variation of the reference 13CO2:12CO2 ratio was 0.06%. Using histology as the 'gold standard', the sensitivity (97.9%) and specificity (95.8%) of the GC-MSD 13C-UBT were comparable to those of other methods of H. pylori diagnosis. A gas chromatograph coupled to a mass selective detector that is available in many analytical and biomedical laboratories can be used for the 13C-UBT. This method will increase the availability and reduce the cost of this non-invasive, non-radioactive diagnostic test.

Chiral-Gas Chromatograpy-Selected Ion Monitoring-Mass Selective Detection Analysis of Secondary Alkaloids in Tobacco and Tobacco Smoke

Abstract Chiral gas chromatography-mass selective detection has been successfully employed in the analysis of secondary alkaloids in selected tobacco materials and cigarette smoke condensate. No extensive sample preparation is involved. A lower detection limit of ~2 % d-nornicotine, d-anabasine and d-anatabine in a mixture of l and d-isomers was achieved. The levels and the enantiomeric ratios of nicotine, nornicotine, anabasine and anatabine varied in different tobacco types. The enantiomeric ratios of nicotine, anabasine and anatabine in mainstream cigarette condensate also varied but were generally representative of the enantiomeric ratios for the alkaloids found in the leaf. The enantiomeric ratio for nornicotine in mainstream cigarette condensate also varied and was not representative of the enantiomeric ratios for the alkaloids found in the leaf. Preferential decomposition or racemization may account for the differences seen in the yields of isomers of nornicotine transferred to the mainstream smoke condensate. An experiment was conducted to determine if the d-nornicotine present in tobacco contributed to the yield of d-nicotine in mainstream smoke condensate. The results of that experiment indicated that the yield of d-nicotine transferred to mainstream smoke did not change significantly when either large levels of endogenous nornicotine were present in the leaf or when large levels of exogenous levels of d-, l-nornicotine were applied to the tobacco rod prior to smoking. The limiting factor in the production of d-nicotine in mainstream cigarette smoke condensate may be the concentration of methyl radicals present to react. Further work must be conducted to unravel the mechanism involved in the production of d-nicotine in cigarette smoke condensate.

Determination of Endosulfans in Soil/Sediment Samples from Point Mugu, Oxnard, California Using Capillary Gas Chromatography/Mass Selective Detection (GC/MSD)

The extent of contamination by endosulfans in soil samples collected from the Point Mugu watershed near Oxnard, California was determined using capillary gas chromatography/mass selective detection (GC/MSD). The study was designed to detect three organochlorinated pesticides: endosulfan α, endosulfan β and endosulfan sulfate. Thirteen sets of two soil samples each were taken from various sites in the region. Our results show that the endosulfan levels in these soils range from trace amounts to nearly 30 ppm, with endosulfan α being the most abundant and endosulfan sulfate the least. Two sites of the study, Hueneme and Revolon and Farm and Revolon, showed high amounts of endosulfans α and β, with concentrations between 20 and 30 ppm. The majority of the other sites studied in this research produced concentrations of less than 10 ppm for each of the three endosulfans monitored. At five areas in particular, Pleasant Valley and Creek, Laguna and Creek, Etting and Creek, Road and Creek and Hueneme and Creek, less than 2 ppm or only trace amounts of endosulfans α, β and sulfate were detected.

Pharmacokinetics of clenbuterol in the ostrich.

The aim of this study was to investigate the pharmacokinetics of clenbuterol in the ostrich as no such data is available. Clenbuterol (2 mg) was given as a single oral dose to nine ostriches. Blood samples were collected over a period of 96 h after administration and urine for a period of 5 d. Plasma and urine samples were frozen at -20 degrees C pending analysis. Clenbuterol was quantified using a gas chromatograph-mass selective detector. The method for quantification of clenbuterol in plasma was validated by analysing spiked quality control samples at different concentrations. The limit of quantification was determined to be 0.75 ng ml-1 with an absolute recovery of more than 80%. The geometric mean maximum plasma clenbuterol concentration was 4.40 ng ml-1 with 3.0 h as the median time for maximum concentration. The plasma elimination half-life was 19.7 h. The clenbuterol concentration was above 0.75 ng ml-1 in plasma for 48 h and above 1.0 ng ml-1 in urine for 5 d. These data can be useful in residue analysis for clenbuterol in ostriches.

Determination of methyl tert-butyl ether and tert-butyl alcohol in human urine by high-temperature purge-and-trap gas chromatography-mass spectrometry.

Methyl tert-butyl ether (MTBE) is the oxygenated gasoline additive most widely used in the U.S. to reduce the CO emission from motor vehicles. We developed a method using a high-temperature purge-and-trap procedure coupled with capillary gas chromatography-mass selective detection to determine MTBE and its metabolite, tert-butyl alcohol (TBA), in human urine. Several spiked-urine tests were conducted at different purging temperatures (25, 55, and 90 degrees C). The results indicated that the purging temperature affects the recovery of TBA from urine more than the recovery of MTBE. The mean recoveries of MTBE and TBA in the urine samples by the high temperature (90 degrees C) purge-and-trap gas chromatography-mass spectrometry method at different spike levels were 96.5+/-4.7% and 98.4+/-5.7%, respectively. The method was used to evaluate the urinary levels in a single subject exposed through inhalation to 1 ppm MTBE for 10 min in a controlled-environment facility. Increases in MTBE and TBA urinary excretion rates were clearly evident following the exposure to MTBE. Approximately 0.9% of the amount of MTBE inhaled was excreted unchanged as urinary MTBE, and 2.4% was excreted as urinary TBA within 10 h after exposure. The method developed is a simple, effective, sensitive, and reproducible procedure for evaluating human exposure to MTBE.

Simultaneous determination of imipramine and its metabolite desipramine in human plasma by capillary gas chromatography with mass-selective detection

An analytical method for the simultaneous determination of imipramine (IMI) and its N-desmethyl metabolite, desipramine (DIMI) in human plasma by capillary gas chromatography–mass selective detection (GC–MS), with D4-imipramine (D4-IMI) and D4-desipramine (D4-DIMI) as internal standards, was developed and validated. After addition of the internal standards, the compounds were extracted from plasma at basic pH into n-heptane–isoamyl alcohol (99:1, v/v), back-extracted into acidic aqueous solution and re-extracted at basic pH into toluene. Desipramine and D4-desipramine were converted into their pentafluoropropionyl derivatives. The compounds were determined by gas chromatography using a mass selective detector at m/ z 234 for IMI, m/ z 238 for D4-IMI, m/ z 412 for DIMI and m/ z 416 for D4-DIMI. The method was applied to clinical samples.

Determination of terrestrial markers in marine environments by gas chromatography—mass-selective detection compared to high-performance liquid chromatography-fluorescence detection

Vanillic acid, syringic acid and often p-hydroxybenzoic acid, were found to be appropriate terrestrial markers in marine sediments, and were analyzed as their n-butyl/acetate esters by gas chromatography with mass-selective detection. The high sensitivity of the method allows terrestrial inputs remote from the source to be measured. Input from angiosperms was the principal terrestrial source in marine sediments. Terrestrial inputs to the outer Great Barrier Reef and the New Guinea Trench were confirmed. The HPLC-fluorescence method is an alternative to the gas chromatography method, providing significantly better sensitivity for syringic acid. Its principal advantage is higher reproducibility.

Identification of Cytochrome P450 3A1/2 as the Major P450 Isoform Responsible for the Metabolism of Fentanyl by Rat Liver Microsomes

The metabolism of fentanyl was investigated using rat liver microsomes to determine whether fentanyl is metabolized by rat liver microsomal cytochrome P450 and, if so, which isoform is responsible for the metabolism. Microsomes isolated from rats pretreated with phenobarbital were more active in metabolizing fentanyl than were microsomes from saline controls. The major metabolic pathway of fentanyl was an oxidative N-dealkylation to norfentanyl, which was detected by a gas chromatograph-mass selective detector (GC-MSD) method. The apparent Vm values for microsomes isolated from saline- and phenobarbital-treated rats were 2 and 9 nmol norfentanyl.min-1.mg-1 microsomal protein, and the apparent Km values were 32 and 47 microM, respectively. Fentanyl metabolism was inhibited by antibodies specific for CYP3A1/2, as well as by chemical inhibitors specific for CYP3A. These results indicate that CYP3A1/2 plays a major role in the oxidation of fentanyl to norfentanyl by rat liver microsomes.

Identification of Cytochrome P450 3A1/2 as the Major P450 Isoform Responsible for the Metabolism of Fentanyl by Rat Liver Microsomes

The metabolism of fentanyl was investigated using rat liver microsomes to determine whether fentanyl is metabolized by rat liver microsomal cytochrome P450 and, if so, which isoform is responsible for the metabolism.Microsomes isolated from rats pretreated with phenobarbital were more active in metabolizing fentanyl than were microsomes from saline controls. The major metabolic pathway of fentanyl was an oxidative N-dealkylation to norfentanyl, which was detected by a gas chromatograph-mass selective detector (GC-MSD) method. The apparent Vm values for microsomes isolated from saline- and phenobarbital-treated rats were 2 and 9 nmol norfentanyl centered dot min-1 centered dot mg-1 microsomal protein, and the apparent Km values were 32 and 47 micro Meter, respectively. Fentanyl metabolism was inhibited by antibodies specific for CYP3A1/2, as well as by chemical inhibitors specific for CYP3A. These results indicate that CYP3A1/2 plays a major role in the oxidation of fentanyl to norfentanyl by rat liver microsomes. (Anesth Analg 1996;82:936-41)

Headspace membrane extraction combined with multiplex gas chromatography and mass selective detector for monitoring of volatile organic compounds

A new analytical method, the membrane extraction with a sorbent interface (MESI) technique in multiplex mode combined with a gas chromatograph/mass selective detector (GC/MSD), has been developed to allow rapid screening analysis and long-term on-line monitoring of volatile organic compounds (VOCs). The advantages of the multiplex MESI system include simplicity, durability, low cost, time efficiency, elimination of solvents, and easy automation. The headspace membrane extraction configuration effectively eliminates the need for a sampling pump and flow metering thus prevents the extraction system from plugging and greatly simplifies the extraction process. The sorbent interface minimizes the loss of analytes by directly connecting the membrane extraction module to the GC/MSD. The sensitivity of the system is significantly enhanced due to the multiplex and high sample throughput advantages. The multiplex technique also reduces the demand on the sorbent interface which allows the use of a simpler interface than the MESI batch technique. The use of a MSD in the selective ion monitoring (SIM) mode not only selectively detects minor components in a sample, but also leads to a significant improvement in the system sensitivity. The MESI program provides an easy-to-use graphical user interface for system automation from sample introduction to report preparation. At optimum experimental conditions, the limit of detection for trichloroethylene in water was 0.5 μg/L, and a RSD below 6% was achieved in the SIM mode. Parameters influencing the sensitivity and precision of the system were studied. Quantitative contaminant determination of a soil leachate sample was performed with the standards addition method. A fumehood air sample was also analyzed using the new method. © 1996 John Wiley & Sons, Inc.

Headspace membrane extraction combined with multiplex gas chromatography and mass selective detector for monitoring of volatile organic compounds

A new analytical method, the membrane extraction with a sorbent interface (MESI) technique in multiplex mode combined with a gas chromatograph/mass selective detector (GC/MSD), has been developed to allow rapid screening analysis and long-term on-line monitoring of volatile organic compounds (VOCs). The advantages of the multiplex MESI system include simplicity, durability, low cost, time efficiency, elimination of solvents, and easy automation. The headspace membrane extraction configuration effectively eliminates the need for a sampling pump and flow metering thus prevents the extraction system from plugging and greatly simplifies the extraction process. The sorbent interface minimizes the loss of analytes by directly connecting the membrane extraction module to the GC/MSD. The sensitivity of the system is significantly enhanced due to the multiplex and high sample throughput advantages. The multiplex technique also reduces the demand on the sorbent interface which allows the use of a simpler interface than the MESI batch technique. The use of a MSD in the selective ion monitoring (SIM) mode not only selectively detects minor components in a sample, but also leads to a significant improvement in the system sensitivity. The MESI program provides an easy-to-use graphical user interface for system automation from sample introduction to report preparation. At optimum experimental conditions, the limit of detection for trichloroethylene in water was 0.5 μg/L, and a RSD below 6% was achieved in the SIM mode. Parameters influencing the sensitivity and precision of the system were studied. Quantitative contaminant determination of a soil leachate sample was performed with the standards addition method. A fumehood air sample was also analyzed using the new method. © 1996 John Wiley & Sons, Inc.

Multiresidue Determination of Pesticides in Fruit and Vegetables by Gas Chromatography–Mass-Selective Detection and Liquid Chromatography with Fluorescence Detection

Abstract A method is described for determining 199 pesticides in fruit and vegetables. Residues are extracted from samples with acetonitrile, and coextractives are removed with a miniaturized charcoal–Celite column cleanup. Analysis is performed by gas chromatography with mass-selective detection in selective-ion monitoring mode. Two injections per sample are required to cover all compounds. Positive analytes are confirmed by retention time and ion ratios. Carbamates are analyzed by liquid chromatography with postcolumn reaction and fluorescence detection. Recovery data were obtained by fortifying 3 matrixes (pears, carrots, and bananas) at 0.1–0.5 ppm. In addition, the method demonstrated acceptable performance for analysis of other crops such as apple, strawberry, orange, pineapple, asparagus, beet, cucumber, tomato, pepper, squash, green peas, potato, and sweet potato. Limits of detection ranged from 0.02 to 0.2 ppm depending on the compound.

Volatile compounds in meromictic Antarctic lakes and basins

Thirteen meromictic Antarctic lakes and basins were sampled for volatile compounds throughout 1991. Their physical characteristics varied widely in surface density (1.01 to 1.16 kg L −1), bottom density (1.03 to 1.19 kg L −1), bottom temperatures (−7.5 to +14.0 °C), bottom redox potential (−420 to +84 mV), maximum depth (7 to 110 m) and depth of oxycline (4 to 47 m). Nineteen compounds were identified and a further eight were tentatively identified using a Gas Chromatograph-Mass Selective Detector (GC-MSD). Volatile compounds detected identified included CS 2, dimethylsulfide, polysulfides, substituted benzenes, thiophenes, octane and 6-methyl 5-hepten-2-one. In general the concentration of volatile compounds increased with depth in the water column with a further increase in concentration was observed in the sediment. The spectiation of volatiles in each site was correlated with its physical characteristics. The predominant environmental factor that influenced the distribution of volatile compounds was density. However, this was modified by the temperature of the water column in heliothermal lakes. Alkyl benzenes were restricted to sites with a bottom density ≤1.08 kg L −1. CS 2 and thiophenes occurred in sites with bottom densities ≤1.15 kg L −1, whereas DMS and the polysulfides occurred in sites with a bottom density ≥1.07 kg L −1. CS 2, thiophenes, DMS and the polysulfides were all found in lakes of intermediate density (1.07–1.14 kg L −1). Some potential sources of the compounds were discussed in relation to the physical nature of the lakes.

Determination of beta-sympathomimetics in liver and urine by immunoaffinity chromatography and gas chromatography—mass-selective detection

A specific and sensitive method for the determination of several β-agonistic drugs in liver and urine is described. Following clean-up by immunoaffinity chromatography and two different derivatizations, gas chromatography—mass spectrometry with electron-impact ionization is performed. The immunoaffinity chromatography columns were packed with Sepharose-immobilized polyclonal antibodies raised against the β-agonist clenbuterol. Owing to the high clean-up efficiency of the immunoaffinity column large sample volumes can be used (up to 100 ml urine or 25 gram liver). The immunoaffinity sample pretreatment is highly specific and no further sample pretreatment was necessary. Due to the combination of two different derivatizations only GC—MS with electron-impact ionization is necessary to fulfil legal requirements. The first confirmation step consists of a derivatization reaction between the hydroxyl group of the parent compound and trimethylsilane. The second confirmation method is a derivatization to a cyclic derivative with the hydroxyl group and the aliphatic nitrogen group. Limits of determination in liver as well in urine are at the 10 ng/kg or ng/l (ppt) level with acceptable signal-to-noise ratio. The method is suitable for identification and quantification of trace amounts of several similar β-agonistic drugs either used separately or in combination and can be used also for quantification of clenbuterol in liver with regard to levels exceeding the maximum residue limit (MRL) of 1 μg/kg (ppb).

Quantification of GR90291 in human blood by high resolution gas chromatography—mass selective detection (HRGC-MSD)

A specific and sensitive high resolution gas chromatography—mass spectrometry method for the determination of GR90291 in human blood is described. The extraction of GR90291 from blood required a polar organic solvent mixture. The crude extract was further purified by successive liquid—liquid partitioning prior to esterification with an HCl—n-butanol solution. This derivative was analysed using a deuterium-labelled internal standard by selected ion monitoring mass spectrometry. The calibration curve ranged from 1 to 100 ng ml −1. The method is reliable for the determination of GR90291 pharmacokinetics in human subjects.

Determination of acenocoumarol in human plasma by capillary gas chromatography with mass-selective detection

A method for the determination of acenocoumarol in human plasma by capillary gas chromatography—mass-selective detection is described. After addition of a structurally related analogue as the internal standard, the compounds are extracted from plasma at acidic pH into toluene, back-extracted with a basic solution and re-extracted from hydrochloric acid solution with toluene, which is then evaporated to dryness. The compounds are converted into their methyl derivatives, which are determined by gas chromatography using a mass-selective detector at m/z 324 for acenocoumarol and m/z 338 for the internal standard. The reproducibility and accuracy of the method were found to be suitable over the acenocoumarol concentrations range 2.2–74 nmol/l. The method could be considered as selective for acenocoumarol in the presence of its major metabolites in plasma.

Determination of anabolic esters in oily formulations and plasma in husbandry using high-performance liquid chromatography and gas chromatography-mass selective detection.

Two different analytical methods are described for the analysis of anabolic steroid esters in oily formulations for veterinary use and animal plasma samples, respectively. For the determination of anabolic steroid esters in oily formulations (at mg kg-1 levels) a reversed-phase high-performance liquid chromatographic method with gradient elution is described. Gradient elution is performed owing to the relatively large variations in polarity of the investigated anabolic steroid esters. For the analysis of anabolic steroid esters in plasma (at ng ml-1 levels) two different strategies are applied. After solid-phase extraction, the plasma samples are introduced into the high-performance liquid chromatography (HPLC) system where the obtained fractions are then analysed by using gas chromatography-mass selective detection (GC-MSD). An alternative method is direct analysis of plasma samples after solid-phase extraction by using GC-MSD without any further clean-up procedure. Prior to GC-MSD the samples are derivatized to corresponding trifluoroacyl (TFA) derivatives. The calibration graph for HPLC is rectilinear over the range 25-150 ng ml-1 plasma and the analytical recoveries for medroxyprogesterone acetate (MPA) and testosterone propionate (TP) are more than 95%. The detection limits for both analytes in GC-MS are 2.5 ng ml-1 plasma for MPA and 0.5 ng ml-1 plasma for TP with an acceptable signal-to-noise ratio (calculated for the derivatized relative molecular mass). In the analysis of plasma obtained from animal experiments concentrations of 6.5 ng ml-1 are found for MPA by using GC-MSD and 5.0 ng ml-1 are found for nortestosterone laurate (NL) by using HPLC.

Determination of succinonitrile in horse urine by gas chromatography-nitrogen-phosphorus detector and gas chromatography-mass spectrometry.

A chromatographic method was developed to detect and confirm the presence of succinonitrile (SDN) in horse urine samples, for antidoping control. The urine samples (5 ml) were extracted with diethyl ether and screened by gas chromatography-nitrogen-phosphorus detector and the confirmation of the drug's presence was accomplished by using gas chromatography-mass selective detection. The recovery of extraction was 78 and 81% for 1.0 and 2.0 micrograms ml-1 (relative standard deviation, < 10%), respectively. Urine samples collected after the administration of Energisan were positive for SDN (1-30 h) in all samples analysed.