Isothermal capillary gas chromatography with electron-capture detection of heptafluorobutyryl-L-prolyl derivatives of chiral amphetamines

Enantioselective trace analysis of amphetamine in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry

A method for the quantitative enantioselective analysis of amphetamine in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry (GC/NICI-MS) is presented. Five-fold deuterated analogues of both enantiomers were used as internal standard. Plasma sample preparation was performed by a rapid liquid-liquid extraction using n-hexane. Derivatization with (S)-(-)-N-(heptafluorobutyryl)prolyl chloride was accomplished directly in the n-hexane extract to avoid loss of amphetamine during sample concentration. The method was validated in the expected concentration range of 0.006 for a pharmacokinetic study. Calibration curves were linear within a range 0.006-50 ng/mL plasma. Precision and accuracy were acceptable over the entire calibration range. Baseline separation of the enantiomers was easily achieved on a 15-m nonchiral apolar column. The method is simple and robust, and has been applied to the batch analysis of amphetamine enantiomers.

Derivatization procedures for gas chromatographic-mass spectrometric determination of xenobiotics in biological samples, with special attention to drugs of abuse and doping agents

The development of low cost MS detectors in recent years has promoted an important increase in the applicability of GC-MS system to analyze for the presence of foreign substances in the human body. Drugs and toxic agents are in vivo metabolized in such a way that more polar compounds are usually formed. Derivatization of these metabolites is often an unavoidable requirement for gas chromatographic analysis. Application of derivatization methods in recent years has been relevant, especially for silylation, acylation, alkylation and the formation of cyclic or diastereomeric derivatives. Given the relevance of drug of abuse testing in modern toxicology, main derivatization procedures for opiates, cocaine, cannabis, amphetamines, benzodiazepines and LSD have been reviewed. Papers describing the analyses of drugs of abuse in matrixes other than blood, such as hair or sweat, have received special attention. Advances in derivatization for sports drug testing have been particularly relevant for anabolic steroids, diuretics and corticosteroids. Among the several methodologies applied, the formation of trimethylsilyl, perfluoroacyl or methylated derivatives have proved to be both versatile and extensively used. Further advances in derivatization for GC-MS applications in clinical and forensic toxicology will depend on the one hand on the degree of further use of GC-MS for routine applications and, on the other hand, on the alternative progress made for developments in LC-MS or CE-MS. Last but not least, the appearance of comprehensive libraries in which reference spectra for different derivatives of many drugs and their metabolites are collected will have an important impact on the expansion of derivatization in GC-MS for toxicological applications.

Gas chromatographic determination of enantiomers as diastereomers following pre-column derivatization and applications to pharmacokinetic studies: a review

The introduction of chiral chromatographic methods has revolutionized the art of separation and quantitation of chiral drugs in biological fluids. A large number of chiral derivatization reagents for various functional groups are available commercially. Therefore, pre-column derivatization methods have become attractive and simple for the gas chromatographic assays in biological fluids. The intent of this article is to review the pre-column chiral derivatization reagents employed in gas chromatographic separations and analyses of enantiomers. A discussion of numerous procedures necessary to develop a quantitative gas chromatographic assay method for drug enantiomers is presented. In this regard, quantitative gas chromatographic assays based on this approach have been applied to investigate the stereoselective pharmacokinetics of several chiral drugs such as fenfluramine, norfenfluramine, methylphenidate, etodolac, propranolol, suprofen and methoxyphenamine.

Stereoselective disposition: enantioselective quantitation of 3,4-(methylenedioxy) methamphetamine and three of its metabolites by gas chromatography/electron capture negative ion chemical ionization mass spectrometry

A new chiral assay for 3,4-(methylenedioxy)methamphetamine (MDMA) and three of its metabolites in biological specimens is based on direct aqueous derivatization with N-heptafluorobutyryl-S-prolyl chloride, followed by capillary chromatographic separation of the diastereomeric derivatives and detection by a mass spectrometer operated in the electron capture negative ion chemical ionization mode. The assay is linear from 5 to 1000 ng ml-1 for each enantiomer and allows simultaneous quantitation of MDMA and three of its metabolites in biological specimens. Investigation of the disposition of racemic MDMA in rats and mice revealed quantitative differences in the disposition of the enantiomers of MDMA in these species; the most noteworthy result was a two-fold greater urinary excretion of the neurotoxic S-(+)-MDMA by mice. Only MDMA and 3,4-(methylenedioxy)amphetamine (MDA) enantiomers were detected at measurable concentrations in the frontal cortices and hippocampis from rats dosed with 10 mg kg-1 of racemic MDMA; in this species the enantiomeric profiles of these two compounds were similar in brain and urine.

Determination of methamphetamine enantiomer ratios in urine by gas chromatography-mass spectrometry

Analysis of the enantiomers of methamphetamine and its metabolite amphetamine is an extremely important process for a number of scientific disciplines. From studies of biological activity and mechanisms through determination of precursor molecules in a criminal investigation are all served by this analytical procedure. Utilization of gas chromatography-mass spectrometry with chiral derivatizing reagents is the most common chiral procedure and produces excellent results. Of the chiral derivatizing reagents available, the most widely used is trifluoroacetyl-l-prolyl chloride (TPC). Utilization of other derivatives require either synthesis by the analyst or have not shown themselves to provide as good a separation as did the TPC reagent. Use of chiral stationary phases yield good results but the disadvantages of temperature limits of these columns and the narrow use to which the columns can be put has limited their utilization. A significant utility of the chiral stationary phase is the ability to determine the purity of a chiral derivatizing reagent. Even if not used for routine analysis of enantiomers, utilization of this procedure can determine the purity of a reagent such as TPC and allow for accurate calculation of actual amounts of each enantiomer. This can be estimated using chiral derivatives on an achiral column, but it is limited to the extent that it is not able to differentiate enantiomeric impurity in the reagent versus the drug itself. Description of chromatographic procedures primarily focusing on gas chromatographic-mass spectrometric techniques but also including liquid chromatographic techniques along with examples of extraction and derivatization procedures is the focus of this review.

Determination of ring- and N-substituted amphetamines as heptafluorobutyryl derivatives

An improved derivatization method for analysing 12 ring- and N-substituted amphetamine-derivatives in body fluids or seized materials by gas chromatograph combined either with mass spectrometer, electron capture or nitrogen phosphorus detector is presented. Heptafluorobutyric anhydride is used as derivatization reagent. No heating or standing period is needed in this procedure. Most of the drugs considered were distinguishable from each other according to their retention times and all of them according to their EI mass spectra. The base peak or one of the most intense peaks in the mass spectra contained benzyl radical and the m/e values were different according to the substituent.

Enantioselective gas chromatographic assay with electron-capture detection for dl-ritalinic acid in plasma

Enantioselective gas chromatographic assays for the quantitation of methylphenidate and its major metabolite ritalinic acid in plasma are described. The procedures involved the extraction of methylphenidate enantiomers from alkanised plasma. The plasma was then washed to ensure complete removal of methylphenidate before saturation with sodium carbonate to promote the extraction of ritalinic acid enantiomers with ethyl acetate-isopropanol (60:40) solvent mixture. Subsequently, ritalinic acid enantiomers were converted back into methylphenidate enantiomers by Fisher-Speier esterification. N-Heptafluorobutyryl-L-prolyl chloride, a chiral acylating reagent, was used to convert the enantiomers of methylphenidate into their corresponding diastereomeric amide derivatives, which were separated cleanly on an achiral capillary column (OV-225) and quantitated with electron-capture detection. The assays were sensitive, reliable and reproducible.