Analytical methodology to determine stable isotopically labelled and unlabelled theophylline in human plasma using capillary gas chromatography-mass spectrometry.

A method is described for the simultaneous determination of [1,3-15N] theophylline and unlabelled theophylline in human plasma using gas chromatography-mass spectrometry. Plasma samples were subjected to extractive alkylation and the stable isotopically labelled and unlabelled forms of the drug were analysed as their N-pentafluorobenzyl derivatives on an SE-52 fused-silica capillary column. Quantitation was made by selected-ion monitoring employing as the internal standard 3-isobutyl-1-methylxanthine. The method has been used to study the absorption kinetics and bioavailability of a sustained release formulation of the drug when co-administered to human volunteers with a conventional formulation of the drug labelled with the stable isotope.

Monitoring exposure to acrylamide by the determination of S-(2-carboxyethyl)cysteine in hydrolyzed hemoglobin by gas chromatography-mass spectrometry.

Acrylamide is a potent cumulative neurotoxin in animals and man. In vivo exposure to this electrophile results in the formation of a covalently bound reaction product with cysteine residues in hemoglobin. This adduct yields on acid hydrolysis S-(2-carboxyethyl)cysteine which has been analyzed by capillary gas chromatography with mass spectrometry. Globin isolated from the blood of rats exposed to acrylamide was spiked with an internal standard (globin treated in vitro with d3-acrylamide) and was then hydrolyzed with 6 N HCl. The protein hydrolysate was fractionated on a Dowex 50W H+ ion exchange column and the amino acids in the partially purified extract were determined as N-heptafluorobutyryl methyl esters using an OV-1701 fused silica capillary column. Quantitation was made by chemical ionization (isobutane) selective ion monitoring in which the ions m/z 386 (M-OCH3)+ derived from derivatized S-(2-carboxyethyl)cysteine in the sample and the corresponding ion m/z 389 from the added deuterium-labeled internal standard were monitored. The dose-response relationship between production of hemoglobin adduct and dose of acrylamide (0.1 mg/kg-5 mg/kg) is curved, showing an increasing slope with increasing doses of acrylamide.

The determination of O,S,S-trimethylphosphorodithioate in the plasma and various tissues of rats using high-resolution gas chromatography with nitrogen-phosphorus detection.

A method has been developed for the determination of O,S,S-trimethylphosphorodithioate in the plasma, lung, liver, brain and thymus of rats using high-resolution gas chromatography. The organophosphorus compound was extracted from the biological sample with ethyl acetate and analysed on a carbowax 20M fused-silica capillary column with a nitrogen-phosphorus specific detector. O,S,S-Triethylphosphorodithioate was used as an internal standard added to the sample before extraction. The sensitivity of the method allowed the compound to be measured in 0.1-ml aliquots of plasma or in 20-mg wet weight of tissue down to a level of 5 ng/sample. The method has been applied to a pharmacokinetic study in the rat after an oral or intravenous dosage with 25 mg/kg of O,S,S-trimethylphosphorodithioate.