Gas Chromatographic-mass Spectrometric Method Research Articles

Human biomonitoring of pyrethrum and pyrethroid insecticides used indoors:: Determination of the metabolites E- cis/ trans-chrysanthemumdicarboxylic acid in human urine by gas chromatography-mass spectrometry with negative chemical ionization

This work describes a gas chromatographic-mass spectrometric method employing negative chemical ionization (NCI) for the determination of E- cis/ trans-chrysanthemumdicarboxylic acid (CDCA) in human urine used as a biomarker for the exposure to pyrethrum and/or certain pyrethroids in insecticide formulations applied indoors. Mixed-mode solid phase extraction was utilized for sample cleanup. Extraction recoveries ranged from 92 to 104% (2–9% R.S.D.). The acids were esterified with 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) allowing both their gas chromatographic separation and their sensitive mass spectrometric detection under NCI conditions. Detection limits of ca. 0.05 μg/l urine were achieved.

Gas chromatographic–mass spectrometric method for the determination of bisphenol A and its chlorinated derivatives in urban wastewater

The simultaneous determination of trace amounts of endocrine disruptors such as bisphenol A (BPA) and its monochloro, dichloro, trichloro and tetrachloro derivatives in wastewater has been developed using gas chromatography–mass spectrometry (GC–MS). Compounds were previously extracted from the aqueous samples using a liquid–liquid extraction procedure with a mixture of dichloromethane:carbon tetrachloride (25/75). After extraction, solvent was removed and a silylation step was carried out with N, O-bis(trimethylsilyl) trifluoroacetamide (BSTFA). The silylated compounds were identified and quantified by GC–MS using an HP1-MS column. The retention times were 6.64 min for BPA silylated, 7.26 min for Cl-BPA silylated, 7.99 min for Cl 2-BPA silylated, 8.85 min for Cl 3-BPA silylated and 9.95 min for Cl 4-BPA silylated. A clean-up is not necessary using SIM mode. Deuterated anthracene ( 2H 10-anthracene) was used as an internal standard. The detection limits obtained were 0.3, 0.6, 2.0, 4.5 and 13.0 ng L –1 for silylated BPA, Cl-BPA, Cl 2-BPA, Cl 3-BPA and Cl 4-BPA, respectively. The proposed method was applied satisfactory to the determination of these chemicals, in different types of wastewater previously spiked with different amounts of these chemicals at concentration levels ranging from 0.01 to 2.50 μg L −1 for BPA, 0.05–2.50 μg L −1 for Cl-BPA and 0.05–5.00 μg L −1 for Cl 2-BPA, Cl 3-BPA and Cl 4-BPA, respectively. The method was validated following standard addition methodology.

Development and validation of a gas chromatographic–mass spectrometric method for simultaneous identification and quantification of marker compounds including bilobalide, ginkgolides and flavonoids in Ginkgo biloba L. extract and pharmaceutical preparations

A gas chromatography–mass spectrometry (GC–MS) method was developed and validated for the simultaneous determination of seven major chemical markers (bilobalide, ginkgolides A, B, C, kaempferol, quercetin and isorhamnetin) in phytopharmaceuticals of Ginkgo biloba L. The intra-day relative standard deviations (RSD) and inter-day RSD’s were based on the analysis of the standardized Ginkgo biloba L. extract on the same day and on the following 3 consecutive days. The intra-day RSD’s ranged from 1.21% (bilobalide) to 6.20% (kaempferol). The inter-day RSD’s ranged from 2.10% (bilobalide) to 10.42% (isorhamnetin). Mean recoveries ranged from a low of 63.0±5.3% (isorhamnetin) to a maximum of 103.5±6.0% (ginkgolide A). Calibration curves were linear in ranges between 2.73 and 36.36 μg/ml for the markers. Limits of detection ranged from a low of 0.5 μg/ml (bilobalide) to a high of 2.5 μg/ml (quercetin). The limits of quantitation were a low of 1.1 μg/ml (gingkolides A, B, C) to a high of 7.5 μg/ml (kaempferol). The method was applied to a standard extract (>6% total terpenoids and >24% total flavonoids) and six ginkgo capsule phytopharmaceuticals.

Validation of a simple gas chromatographic–mass spectrometric method for the determination of gamma-butyrolactone in human plasma

A gas chromatographic–mass spectrometric (GC–MS) method is described for the determination of human plasma levels of gamma-butyrolactone (GBL) is described. The method is sensitive and simple. The plasma sample spiked with the internal standard was extracted by dichloromethane (CH 2Cl 2) in acidic conditions, and the concentrated organic layer was injected into GC–MS. Because of endogenous GBL in human plasma, the method used a standard calibration curve. The calibration curve was linear from 10 to 1000 ng/ml. The method has been validated for accuracy and precision with the relative error and C.V. for intra- and inter-day within 10%. GBL-spiked plasma samples stored at −80 °C were stable for a 3-month period. The stability of plasma samples after three cycles of freezing and thawing and of prepared samples on an autosampler for 48 h were demonstrated. Plasma concentrations of GBL before and after administration of UFT were 24.3±14.2 and 84.9±22.4 ng/ml, respectively.

New gas chromatographic–mass spectrometric method for the determination of urinary pyrethroid metabolites in environmental medicine

We have developed and validated a new, reliable and very sensitive method for the determination of the urinary metabolites of the most common pyrethroids in one analytical run. After acidic hydrolysis for the cleavage of conjugates, the analytes cis-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid ( cis-Cl 2CA), trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid ( trans-Cl 2CA), cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (Br 2CA), 4-fluoro-3-phenoxybenzoic acid (F-PBA) and 3-phenoxybenzoic acid (3-PBA) were extracted from the matrix with a liquid–liquid extraction procedure using n-hexane under acidic conditions. For further clean-up, NaOH was added to the organic phase and the carboxylic acids were re-extracted into the aqueous phase. After acidification and extraction into n-hexane again, the metabolites were then derivatised to volatile esters using N- tert.-butyldimethylsilyl- N-methyltrifluoroacetamid (MTBSTFA). Separation and detection were carried out using capillary gas chromatography with mass-selective detection (GC–MS). 2-Phenoxybenzoic acid (2-PBA) served as internal standard for the quantification of the pyrethroid metabolites. The limit of detection for all analytes was 0.05 μg/l urine. The RSD of the within-series imprecision was between 2.0 and 5.4% at a spiked concentration of 0.4 μg/l and the relative recovery was between 79.3 and 93.4%, depending on the analyte. This method was used for the analysis of urine samples of 46 persons from the general population without known exposure to pyrethroids. The metabolites cis-Cl 2CA, trans-Cl 2CA and 3-PBA could be found in 52, 72 and 70% of all samples with median values of 0.06, 0.11 and 0.16 μg/l, respectively. Br 2CA and F-PBA could also be detected in 13 and 4% of the urine samples.

Analysis of cigarette mainstream smoke for 1,1-dimethylhydrazine and vinyl acetate by gas chromatography-mass spectrometry.

1,1-Dimethylhydrazine, also known as unsymdimethylhydrazine (UDMH) and vinyl acetate (VA), are both classified by the International Agency for Research on Cancer as 2B carcinogens (possibly carcinogenic to humans) and listed as cigarette smoke constituents; however, there is little or no quantitative data available on them. For UDMH in cigarette smoke, neither a yield nor a method has been published. For VA, the most recent information on yields dates back to 1965. To bridge this gap, we have developed new gas chromatographic-mass spectrometric methods for both compounds to determine their yields in cigarette smoke. UDMH is determined by derivatization with 2-nitrobenzaldehyde in methanol and is not found in cigarette smoke at levels above the detection limit of 19 ng/cig. In further experiments, when UDMH is added to the smoke stream or air stream of lit or unlit cigarettes, the derivative 2-nitrobenzaldehyde-2,2-dimethylhydrazone is found only in the air stream of the unlit cigarettes. From this, we conclude that UDMH is either not formed during smoking at all or, if it is, it reacts immediately and quantitatively with other smoke constituents (e.g., aldehydes) and is therefore not detectable in cigarette smoke. VA is determined by trapping in acetone at -78 degrees C and is found at a concentration of 270 ng/cig for a standard reference cigarette with a cellulose acetate filter (the reference cigarette 1 R4F). In the literature, VA is reported at concentrations of 1.6 microg/cig for a cigarette with a cellulose acetate/charcoal filter and 4 microg/cig for a cigarette with a cellulose acetate filter and for an unfiltered cigarette.

Effects of oxidizing adulterants on detection of 11-nor-delta9-THC-9-carboxylic acid in urine.

Bleach, nitrite, chromate, and hydrogen peroxide-peroxidase are effective urine adulterants used by the illicit drug users to conceal marijuana-positive results. Methods for detecting nitrite and chromate are available. Effects of other oxidizing agents that could possibly be used as adulterants and are difficult to detect or measure are presented in this report. Urine samples containing 40 ng/mL of 11-nor-delta9-THC-9-carboxylic acid (THC-acid) were treated with 10 mmol/L of commonly available oxidizing agents. Effects of horseradish peroxidase of activity 10 unit/mL and extracts from 2.5 g of red radish (Raphanus sativus, Radicula group), horseradish (Armoracia rusticana), Japanese radish (Raphanus sativus, Daikon group), and black mustard seeds (Brassica nigra), all with 10 mmol/L of hydrogen peroxide, were also examined. After 5 min, 16 h and 48 h of exposure at room temperature (23 degrees C) the specimens were tested by a gas chromatographic-mass spectrometric method for THC-acid. A control group treated with sodium hydrosulfite to reduce the oxidants, was also tested to investigate the effect of oxidizing agents on THC-acid in the extraction method. THC-acid was lost completely in the extraction method when treated with chromate, nitrite, oxone, and hydrogen peroxide/ferrous ammonium sulfate (Fenton's reagent). Some losses were also observed with persulfate and periodate (up to 25%). These oxidants, and other oxidizing agents like permanganate, periodate, peroxidase, and extracts from red radish, horseradish, Japanese radish and black mustard seeds destroyed most of the THC-acid (> 94%) within 48 h of exposure. Chlorate, perchlorate, iodate, and oxychloride under these conditions showed little or no effect. Complete loss was observed when THC-acid was exposed to 50 mmol/L of oxychloride for 48 h. Several oxidizing adulterants that are difficult to test by the present urine adulterant testing methods showed considerable effects on the destruction of THC-acid. The time and temperature for these effects were similar to those used by most laboratories to collect and test specimens. In several cases, the loss of THC-acid was > 94%.

Gas chromatographic–mass spectrometric method for quantification of 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone in chlorinated water samples

A method for the determination of 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), in drinking water by GC–MS with a limit of detection of 3.0 μg/l and a limit of quantification of 7.0 μg/l is presented. Clean-up by SPE and extraction of water samples with dichloromethane were carried out before the preconcentration of MX, which was derivatized directly in the injector of the GC, and the MX trimethylsilyl derivative was identified and quantitatively determined by MS.

Gas chromatographic–mass spectrometric method for the determination of alkylresorcinols in human plasma

Alkylresorcinols can be found in high amounts in whole grain cereals, especially in rye. Previously it has not been possible to measure alkylresorcinols in plasma. In this paper a validated gas chromatographic–mass spectrometric method for the quantitative determination of alkylresorcinols with chain lengths of C15:0, C17:0, C19:0, C21:0, and C23:0 in human plasma samples is presented. Other alkylresorcinols may be measured with the method as well, but their assay was not validated in this work. In this work also the amount of alkylresorcinol C25:0 was measured. The pretreatment of plasma samples consists of a simple incubation, an extraction with diethyl ether and a chromatographic purification before the GC-MS analysis. As internal standard an alkylresorcinol C20:0 was used. The validation of the method showed that it fulfilled the reliability criteria. Calibration graphs were linear over the range of 4.1–660 pg per injection. The mean recovery percentage was 112±10.8%. Our results show that the alkylresorcinols are found in plasma in the same ratio, as found in rye grains, according to literature. The alkylresorcinols were in the unconjugated form. The total amounts of alkylresorcinols in two plasma samples analyzed here were 333 and 381 nmol/L.

Validation of a microdialysis–gas chromatographic–mass spectrometric method to assess 8-methoxypsoralen in psoriatic patient dermis

8-Methoxypsoralen (8-MOP) is currently used in PUVA therapy (psoralen+UVA) to treat dermatological diseases such as psoriasis, vitiligo and atopic dermatitis. The aim of this work was to validate a method for collecting 8-MOP from patient dermis by a non invasive technique, microdialysis, and then to assess this molecule by gas chromatography–mass spectrometry (GC–MS). 5-Methoxypsoralen (5-MOP) was used as an internal standard. The calibration curve demonstrated a linear relationship between the peak areas of 8-MOP and 5-MOP over a wide range of 8-MOP concentrations (0.9–100 ng/ml). Within- and between-run precisions were measured, using four different 8-MOP concentrations, which varied from 98.0 to 102.0% and from 98.5 to 101.8%, respectively. The limits of detection and quantification were 0.29 and 0.52 ng/ml, respectively. The method was validated and then applied to determine the pharmacokinetic of 8-MOP in ten psoriatic patient dermis, after oral intake of this drug. The results demonstrated that the association of microdialysis with the GC–MS method was an efficient procedure to collect and assess 8-MOP in human dermis, in vivo.

Analysis of acrylamide, a carcinogen formed in heated foodstuffs.

Reaction products (adducts) of acrylamide with N termini of hemoglobin (Hb) are regularly observed in persons without known exposure. The average Hb adduct level measured in Swedish adults is preliminarily estimated to correspond to a daily intake approaching 100 microg of acrylamide. Because this uptake rate could be associated with a considerable cancer risk, it was considered important to identify its origin. It was hypothesized that acrylamide was formed at elevated temperatures in cooking, which was indicated in earlier studies of rats fed fried animal feed. This paper reports the analysis of acrylamide formed during heating of different human foodstuffs. Acrylamide levels in foodstuffs were analyzed by an improved gas chromatographic-mass spectrometric (GC-MS) method after bromination of acrylamide and by a new method for measurement of the underivatized acrylamide by liquid chromatography-mass spectrometry (LC-MS), using the MS/MS mode. For both methods the reproducibility, given as coefficient of variation, was approximately 5%, and the recovery close to 100%. For the GC-MS method the achieved detection level of acrylamide was 5 microg/kg and for the LC-MS/MS method, 10 microg/kg. The analytic values obtained with the LC-MS/MS method were 0.99 (0.95-1.04; 95% confidence interval) of the GC-MS values. The LC-MS/MS method is simpler and preferable for most routine analyses. Taken together, the various analytic data should be considered as proof of the identity of acrylamide. Studies with laboratory-heated foods revealed a temperature dependence of acrylamide formation. Moderate levels of acrylamide (5-50 microg/kg) were measured in heated protein-rich foods and higher contents (150-4000 microg/kg) in carbohydrate-rich foods, such as potato, beetroot, and also certain heated commercial potato products and crispbread. Acrylamide could not be detected in unheated control or boiled foods (<5 microg/kg). Consumption habits indicate that the acrylamide levels in the studied heated foods could lead to a daily intake of a few tens of micrograms.

Rapid simultaneous determination of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine, and 3,4-methylenedioxyethylamphetamine in urine by solid-phase extraction and GC-MS: a method optimized for high-volume laboratories.

To facilitate analysis of high sample volumes, an extraction, derivatization and gas chromatographic-mass spectrometric analysis method was developed to simultaneously determine amphetamine (AMP), methamphetamine (MAMP), 3,4-methylenedioxyamphetamine (MDA) 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDEA) in urine. This method utilized a positive-pressure manifold cation-exchange polymer-based solid-phase extraction followed by elution directly into automated liquid sampler (ALS) vials. Rapid derivatization was accomplished using heptafluorobutyric anhydride (HFBA). Recoveries averaged 90% or greater for each of the compounds. Limits of detection were 62.5 ng/mL (AMP and MDEA), 15.6 ng/mL (MAMP), and 31.3 ng/mL (MDA and MDMA) using a 2-mL sample volume. The method was linear to 5000 ng/mL for all compounds using MDMA-d5 and MAMP-d14 as internal standards. Over 200 human urine samples previously determined to contain the target analytes were analyzed using the method. Excellent agreement was seen with previous quantitations. The method was challenged with 75 potentially interfering compounds and no interferences were seen. These interfering compounds included ephedrine, pseudoephedrine, phenylpropanolamine, and phenethylamine. The method resulted in dramatic reductions in processing time and waste production.

Measurement of 4-hydroxynonenal in small volume blood plasma samples: modification of a gas chromatographic–mass spectrometric method for clinical settings

4-Hydroxynon-2-enal (4-HNE) is one of the major aldehydic products of lipid peroxidation (LPO) and is involved in a number of pathophysiological processes. Since LPO products are useful indicators for oxidative stress in vivo, a number of detection methods for LPO products in biological tissues were developed. However, none of these methods is presently used in clinical settings. In order to introduce LPO products as biomarkers in clinical studies a suitable GC–MS method for 4-HNE detection was adapted to meet clinical requirements. As one result, the minimal sample volume could be decreased to 50 μl of plasma so that the method might even be suitable for pediatric purposes. The best internal standard (I.S.) for 4-HNE detection by GC–MS 9,9,9- D 3-4-hydroxynon-2-enal was introduced by van Kuijk et al. [Anal. Biochem., 224 (1995) 420]. However, because of its limited availability, benzaldehyde-ring- d 5, 4-hydroxybenzaldehyde, and 2,5-dihydroxybenzaldehyde were tested to find an alternative. Out of these three, 4-hydroxybenzaldehyde was shown to serve best as I.S. To examine the applicability of the adapted method, tests on the stability of 4-HNE in samples during storage were carried out. It was shown that plasma samples need to be stored at −80 °C or less to avoid greater loss of 4-HNE. Samples with 4-HNE concentrations close to the physiological level were shown to be stable over 22 months at −80 °C. The introduction of a new and easily available I.S., reduction of the sample volume, and information about sample stability provided by this study facilitate 4-HNE determination in most clinical settings.

Validated method for quantitation of biomarkers for benzene and its alkylated analogues in urine

A validated gas chromatography–mass spectrometric method for the analysis of the metabolites of benzene and its alkylated analogues in urine is reported. A number of metabolites, as required by authorities for biomonitoring of industrial exposure to aromatic vapour, were analysed simultaneously with preservation of quantitative information concerning positional isomers. The use of this method replaces a combination of analytical methods required for the analysis of all these metabolites. Urine samples were subjected to acidic deconjugation followed by a derivatization step. Phenol, ortho-, meta-, para-cresol, mandelic acid, and ortho-, meta-, para-methylhippuric acid were analysed as their corresponding ethoxycarbonyl derivatives, with single ion monitoring. The mass-to-charge ratios ( m/ z) of the ions used for quantitation by single ion monitoring of the metabolites were: phenol, 94 m/ z; cresols, 108 m/ z; mandelic acid, 206 m/ z; hippuric acid, 105 m/ z; methylhippuric acids, 119 m/ z. The mass-to-charge ratios for the internal standards were: [ 2H 6]phenol, 99 m/ z; p-chlorophenol, 128 m/ z and 3-chloro-4-hydroxyphenyl acetic acid, 214 m/ z. The limits of detection for phenol and the cresols were below 0.4 μmol/l and below 0.05 μmol/l for mandelic acid and the hippuric acids. Within-run precision for mandelic acid was 6.2%, for hippuric acid was 7.32% and was below 5% for the rest of the analytes.

Rapid and sensitive determination of nalmefene in human plasma by gas chromatography–mass spectrometry

A rapid gas chromatography–mass spectrometric method for the determination of nalmefene in human plasma is described. The procedure involves protein precipitation, extraction with ethanol–chloroform mixture and derivatization with pentafluropropionic anhydride. The deuterated analog of nalmefene, 6β-naltrexol- d 7, was used as the internal standard. Quantitation was achieved on a HP-1 column (12 m×0.2 mm I.D.) with negative chemical ionization (NCI) using methane:ammonia (95:5) as the reagent gas. The standard curves were fitted using a quadratic equation with the curve encompassing a range of 0.5 to 200 ng/ml, and the intra- and inter-assay variations for three different nalmefene levels were less than 10% throughout. The limit of quantitation was found to be 0.5 ng/ml. The method described is highly specific and reproducible, and could also be applied for the determination of naltrexone and 6β-naltrexol. Application of the method to actual human plasma samples is demonstrated.

Solid-phase microextraction–gas chromatographic–mass spectrometric method for the determination of the fungicides cyprodinil and fludioxonil in white wines

A solid-phase microextraction (SPME) followed by a gas chromatographic–mass spectrometric (GC–MS) determination has been developed and validated for the determination of cyprodinil and fludioxonil in white wine samples. Extraction parameters such as the selection of SPME coating, the effect of the temperature, the effect of the headspace volume and the salt addition were studied and optimized, together with GC–MS analytical conditions. The divinylbenzene–Carboxen–polydimethylsiloxane (DVB–CAR–PDMS) fiber was the most appropriate for the determination of the two pesticides in wine. The quality parameters of the proposed method demonstrated a good precision (RSD about 5%), with detection limits of 0.1 and 0.2 μg/l for cyprodinil and fludioxonil, respectively. Fifteen commercial white wine samples produced in Rı́as Baixas area in Galicia (N.W. Spain) were analyzed with the SPME–GC–MS procedure. Some of the commercial wines (75%) presented the two pesticides in concentrations ranging from 0.9 to 28.6 μg/l. In conclusion, SPME–GC–MS has a great potential for fungicide determination in wines.

The determination of biperiden in plasma using gas chromatography mass spectrometry: pharmacokinetics after intramuscular administration to guinea pigs.

A gas chromatographic-mass spectrometric (GC-MS) method has been developed for the analysis of the biperiden from plasma. The method utilizes 290 microl of plasma and a simple hexane extraction/clean-up procedure. Standard curves were linear over the range of 1.9-250 ng/mL. The range of correlation coefficients for the individual standard curves was 0.9984-0.9999; the largest coefficient of variation expressed as a percentage (% CV) was 11.5%. Precision and accuracy were examined by assessing between-day and within-day variability. For between-day precision, the % CVs ranged from 2.86 to 5.17%. Accuracy as expressed by percentage error ranging from -2.16 to 5.83%. The study for within-day precision demonstrated % CVs from 0.95 to 5.55% with accuracy from -3.37 to 2.45%. Applicability of the method was demonstrated by examining the pharmacokinetics of intramuscular (i.m.) biperiden as an anticonvulsant treatment in a guinea pig model for organophosphate (OP)-induced seizure activity. Mean pharmacokinetic parameter estimates were similar to literature values; selected mean pharmacokinetic parameter estimates were: apparent volume of distribution, 13.9 L/kg; half-life of elimination, 93 min; time to maximal plasma concentration, 27.4 min; and maximal plasma concentration, 32.22 eta g/mL. The time to maximal plasma concentration was found to be similar to the onset time for terminating OP-induced seizure activity in guinea pigs receiving biperiden as an anticonvulsant treatment. The studies indicate that the method affords the required precision, accuracy and sensitivity to assay biperiden at the doses utilized for these pharmacokinetic studies after i.m. administration to guinea pigs.

Rapid and sensitive analysis of medroxyprogesterone acetate in human serum by gas chromatography-mass spectrometry

Medroxyprogesterone acetate (MPA) is one of the major drugs used in endocrine therapy for advanced or recurrent breast cancer. The present study describes an accurate and reproductible gas chromatographic-mass spectrometric(GC-MS) method to measure MPA in serum.

Measurement of ketoprofen in horse urine using gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric (GC-MS) method for the determination of ketoprofen, a non-steroidal anti-inflammatory drug (NSAID), in horse urine by selected ion monitoring (SIM) mode is described. Urine samples (2 mL) were extracted by liquid-liquid extraction with diethyl ether. The residues were then evaporated, derivatized and injected into the GC-MS system. Validation of the GC-MS method in the SIM mode using flurbiprofen as the internal standard (IS) included linearity studies (10-10 000 ng/mL), recovery (95%) and limit of quantitation (LOQ) (10 ng/mL). The response was linear, with a correlation coefficient (0.9998) for ketoprofen. When applied to horse urine samples, the present method allowed detection of ketoprofen up to 16 days in FULL SCAN mode after a topical application of 1.1 g of ketoprofen in a gel formulation.

Simultaneous determination of melatonin and pyridoxine in tablets by gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric (GC-MS) method for the qualitative and quantitative determination of melatonin plus pyridoxine commercial tablets is described. Melatonin and pyridoxine were simultaneously determined by GC-MS after extraction from ground tablets with methanol and derivatization with N-methyl-N-N-trimethlylsilyltrifluoroacetamide (MSTFA). The mass chromatograms were generated using 232 m/z ion for melatonin and 280 m/z ion for pyridoxine, respectively. Splitless injection offers good reproducibility with a standard deviation of 2%. The developed method was applied to analyze the melatonin and pyridoxine content from two different tablet formulations. Also, recovery, detection and quantification limits are reported.