Pentafluorobenzenesulfonyl chloride: a new electrophoric derivatizing reagent with application to tyrosyl peptide determination by gas chromatography with electron capture detection

A rapid, sensitive electron-capture gas chromatographic procedure for analysis of metabolites of N-methyl,N-propargylphenylethylamine, a potential neuroprotective agent

INTRODUCTION

N-Methyl,N-propargyphenylethylamine (MPPE) is a novel analog of (-)-deprenyl, a drug prescribed for Parkinson's disease and shown to have neuroprotective and neurorescue properties in a wide variety of in vitro and in vivo models. MPPE is also neuroprotective, but has the advantage over (-)-deprenyl of not being metabolized to amphetamine or N-methylamphetamine.

METHOD

In this paper, extractive derivatization with pentafluorobenzenesulfonyl chloride (PFBSC) followed by electron-capture gas chromatography was utilized to study the metabolism of MPPE.

RESULTS

The procedure is rapid and reproducible, giving derivatives with excellent chromatographic properties. Using this procedure, it has now been shown that beta-phenylethylamine (PEA), N-methylphenylethylamine (N-methylPEA) and N-propargylphenylethylamine (N-propargylPEA) are formed from MPPE during incubation of this drug with human liver microsomes. Levels of all three metabolites were shown to increase with increasing time of incubation with the microsomes.

DISCUSSION

Extractive derivatization with PFBSC followed by electron-capture gas chromatography represents an efficient means of separating and quantitating the metabolites of MPPE, a novel neuroprotective agent.

Simultaneous determination of fluoxetine and its metabolite p-trifluoromethylphenol in human liver microsomes using a gas chromatographic-electron-capture detection procedure

An gas chromatography-electron-capture detection method has been developed for simultaneous determination of fluoxetine and p-trifluoromethylphenol (TFMP), an O-dealkylated metabolite of fluoxetine in human liver microsomes. Prior to the analysis, aliquots of alkalinized microsomal mixture were extracted with ethyl acetate solvent containing acetonitrile (10%, v/v) and the derivatizing reagent, pentafluorobenzenesulfonyl chloride (0.1%, v/v). The organ phase was retained and taken to dryness, the residue was reconstituted in methanol, and the aliquot of extracts was injected directly into a gas chromatograph equipped with an electron-capture detector. 2,4-Dichlorophenol was added to the initial incubation mixture and carried through the procedure as the internal standard. The method provided the mean recoveries of up to 103% for fluoxetine and 104% for TFMP. Acceptable relative standard deviations were found for both within-run and day-to-day assays. The practical limit of detection (signal-to-noise ratio=3) was 1.62 ng/ml for TFMP and 6.92 ng/ml for fluoxetine in human liver microsomes, and the limit of quantitation was 8.1 pg for TFMP and 34.6 pg for fluoxetine. The assay is rapid and sensitive and has been applied successfully to simultaneous quantification of fluoxetine and TFMP in human liver microsomes with different CYP2C19 genotypes.

A rapid method of determining amphetamine in plasma samples using pentafluorobenzenesulfonyl chloride and electron-capture gas chromatography

INTRODUCTION

Acute administration of (+)-amphetamine has been used as a model for mania in humans since it mimics the physiological, biochemical, and cognitive effects seen in mania. A rapid and sensitive method for the determination of amphetamine in human plasma samples using gas chromatography with electron-capture detection was developed in our laboratory to follow the time course of amphetamine levels in patients receiving this drug as part of a study using amphetamine as a model for mania.

METHODS

Blood samples were taken from healthy male volunteers at 30, 60, 90, 150, 210, 240, and 480 min after administration of 25 mg of (+)-amphetamine. Plasma was isolated by centrifugation and used for the analysis. This method is a modification of the procedure described by Paetsch et al. [J. Chromatogr. 573 (1992) 313] for the determination of amphetamine in rat brain tissue. Amphetamine was derivatized under basic conditions using pentafluorobenzenesulfonyl chloride (PFBSC) prior to analysis on a gas chromatograph equipped with a capillary column and an electron-capture detector. The internal standard used was benzylamine. The structure of the amphetamine derivative was confirmed using combined gas chromatography-mass spectrometry (GC-MS).

RESULTS

The limit of detection was <1 ng/ml, and the method was linear in the 1- to 100-ng range used. Mean amphetamine levels peaked at 3.5 h after drug administration, and were 40.8 +/- 1.5 ng/ml at that time.

DISCUSSION

This procedure produces a stable derivative with excellent chromatographic properties and is both simple and reproducible.

Determination of p-trifluoromethylphenol, a metabolite of fluoxetine, in tissues and body fluids using an electron-capture gas chromatographic procedure

An electron-capture gas chromatographic procedure was developed for the analysis of p-trifluoromethylphenol, an O-dealkylated metabolite of fluoxetine, in biological samples. A basic extraction of the biological sample was employed, followed by derivatization with pentafluorobenzenesulfonyl chloride. The internal standard, 2,4-dichlorophenol, was added to all samples used in the procedure to aid in quantitation. The practical limit of detection (signal-to-noise ratio>3) for p-trifluoromethylphenol was <5 ng/ml in human plasma samples, <10 ng/g of rat brain tissue, <25 ng/g of rat liver tissue and <25 ng/ml in human and rat urine samples. In the rat, the levels of free p-trifluoromethylphenol in the liver were 10-fold higher than those in the brain, and a substantial amount was excreted in the urine. Human urine samples contained levels of free p-trifluoromethylphenol approximately 30-fold higher than those found in human plasma samples. The procedure described is useful for the detection and quantitation of free p-trifluoromethylphenol in humans and rats treated with fluoxetine.

Electron-capture gas chromatographic procedure for simultaneous determination of amphetamine and N-methylamphetamine

An electron-capture gas chromatographic procedure for the simultaneous determination of amphetamine and N-methylamphetamine in biological samples is described. The method employs extraction with the ion-pairing reagent bis(2-ethylhexyl)phosphoric acid, and back-extraction with 0.5 M hydrochloric acid. The hydrochloric acid phase is basified, and the amphetamines and the internal standard benzylamine are derivatized with pentafluorobenzenesulfonyl chloride prior to analysis on a gas chromatograph equipped with a capillary column. Levels of amphetamine and N-methylamphetamine have been determined in the urine and liver of rats treated chronically with (-)-deprenyl.

Preparation of electrophoric derivatives of N7-(2-hydroxyethyl)guanine, an ethylene oxide DNA adduct

Ethylene oxide, a potential human carcinogen, mainly damages DNA by reacting at guanine sites to form N7-(2-hydroxyethyl)guanine. In order to determine this DNA adduct with high sensitivity by gas chromatography, we have prepared, for comparison purposes, four electrophoric derivatives. The two that are most promising to date are bis- and tris-pentafluorobenzyl products prepared by first chemically transforming the N7-(2-hydroxyethyl)guanine to a corresponding xanthine, and then reacting the latter with pentafluorobenzyl bromide. These two derivatives are obtained in good yields and give molar responses of 0.6 and 0.5, respectively, relative to that of lindane by gas chromatography with electron-capture detection.

Determination of 5-methylcytosine in DNA by gas chromatography-electron-capture detection

The following sequence of analytical steps was used to determine the amount of 5-methylcytosine (mol-%) in calf thymus and human lymphocyte DNA:acid hydrolysis of the DNA, derivatization (pentafluorobenzyl bromide, solid phase extraction, pivalic anhydride), internal standard addition, solid phase extraction, high-performance liquid chromatography, and gas chromatography with electron-capture detection. The steps were carefully optimized, leading to a recovery of 30 +/- 1.0% starting with a nucleobase standard containing 1.25 ng of 5-methylcytosine. A second analysis of this sample gave a 30 +/- 0.3%, demonstrating a high precision for the method. In good agreement with earlier work by others, 1.2 +/- 0.10 mol-% of 5-methylcytosine was then found in a 350 ng sample of calf thymus DNA, and values of 0.9 +/- 0.07 and 0.8 +/- 0.04 mol-% (two runs) were found in hyman lymphocyte DNA.

Sample preparation for gas chromatography with electron capture detection: determination of total and free thyroxin in serum

Relatively clean gas chromatography with electron capture detection (GC-ECD) chromatograms are obtained for both total and free thyroxin (T4) in serum by improving sample preparation. This is based on establishing a sequence of steps that cumulatively overcome two classes of interference: those present in the initial sample and those introduced by the procedure. The main source for the latter contaminants is the derivatization step, a problem that was largely overcome by employing HPLC after this step. Also it is helpful to use ion-exchange columns early in the procedure under fast-flow conditions with intermediate flows of air to speed up and enhance their reliability. The work establishes some guidelines for future applications of GC-ECD to the determination of sub-nanogram analytes requiring derivatization, an area in which GC-ECD has been remiss in the past. As a side benefit, total T4 in serum is determined by HPLC for the first time with uv detection.

Electron-capture gas chromatographic analysis of beta-phenylethylamine in tissues and body fluids using pentafluorobenzenesulfonyl chloride for derivatization

A gas chromatographic procedure is described for the analysis of beta-phenylethylamine (PEA) in tissues and body fluids. The method involves the use of pentafluorobenzenesulfonyl chloride for extraction and derivatization of PEA. This is followed by separation and analysis of the derivatized amine on a gas chromatograph equipped with a fused-silica capillary column and an electron-capture detector. The procedure is rapid, provides a stable and sensitive derivative, and has been applied to analysis of PEA in brain, heart, kidney, liver, lung, spleen and blood from the rat and urine from human subjects.

Single-step, quantitative derivatization of amino, carboxyl, and hydroxyl groups in iodothyronine amino acids with ethanolic pivalic anhydride containing 4-dimethylaminopyridine

Reaction of thyroxine with ethanol and pivalic anhydride in the presence of 4-dimethylaminopyridine quantitatively forms N,O-dipivalyl thyroxine ethyl ester. Other iodothyronines react similarly and the procedure is moisture insensitive. Apparently this reaction is successful, in contrast to similar procedures reported for the derivatization of alpha-amino acids, because it overcomes the problem in other procedures of irreversible side reactions arising from an oxazolone intermediate.