Gas chromatography of barbiturates, phenolic alkaloids, and xanthine bases: flash-heater methylation by means of trimethylanilinium hydroxide

Intra-injector methylation of free fatty acids from aerobically and anaerobically cultured Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

Free fatty acids from the type strains of anaerobically and aerobically broth-cultured Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus cells were Soxhlet-extracted with hexane. The fatty acids were identified and quantified by gas chromatography and gas chromatography-mass spectrometry after intra-injector derivation with trimethylanilinium hydroxide. This derivatization method, which we propose as suitable for routine use in clinical microbiology, is fast, accurate and sensitive, with low toxicity. Whereas the fatty acid content of A. actinomycetemcomitans was affected by the cultivation atmosphere, i.e. C16:1, decreased under aerobic growth and C16:0 increased, that of the closely related H. aphrophilus was more stable.

Correlation of sedative effects with brain levels of barbiturates in LS and SS mice

Long-sleep (LS) and short-sleep (SS) mice, genetically selected for their differential CNS sensitivity to ethanol, have also been shown to differ in their response to other sedative-hypnotics, including the barbiturates. We have applied a gas-chromatographic method of analysis of brain barbiturate concentrations following IP administration of either the water-soluble barbiturate diethylbarbital (DB) or the lipid-soluble barbiturate secobarbital (SB). Brain barbiturate levels were assessed at loss of righting response, and at regaining righting response (waking). In addition, latency to loss of righting response and duration of loss of righting response were measured following IP barbiturate administration. We have observed a differential sensitivity of LS and SS mice to the sedative effects of DB, with LS mice having greater sensitivity compared to SS. This differential sensitivity to DB, as measured by a lower concentration of DB which caused loss of righting in LS, was accompanied by an equal rate of water-soluble barbiturate brain distribution and elimination in the two lines. With the lipid-soluble barbiturate SB, LS and SS mice did not differ in brain SB concentration at loss of righting response or at waking. However, sleep time was much longer in SS mice than LS due to slower brain clearance of the barbiturate in SS. Therefore, duration of loss of righting (sleep time) did not adequately reflect central sensitivity to the lipid-soluble barbiturate. These data suggest the importance of quantifying brain concentrations at loss of righting reflex when assessing central sensitivity to sedative-hypnotic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of antiepileptic drugs

The present paper reviews gas and liquid chromatographic methods for the determination of the most commonly monitored antiepileptic drugs: phenobarbital, phenytoin, carbamazepine, primidone, ethosuximide, valproic acid and clonazepam along with a new compound, progabide. The individual classes of drugs are first treated separately to highlight specific aspects of their quantification, and this is followed by an overview of those methods permitting the concomitant analysis of two or more antiepileptic compounds. Sample preparation techniques as well as comparisons between chromatographic and other techniques are treated more fully in separate sections.

Quantitative analysis of veralipride in plasma and urine by gas chromatography-mass spectrometry and gas chromatography with flame-ionization detection

A highly sensitive and selective quantitative assay for unchanged veralipride has been developed. The compound is extracted from alkalized samples (plasma or urine) with dichloromethane and converted to its trimethylated derivative by reaction with trimethylanilinium hydroxide. The reaction mixture is then chromatographed on a 3% OV-1 column. Trimethylated derivatives of plasma samples were assayed by selected-ion monitoring in the chemical-ionization mode and quantified by comparing the intensity of the quasi-molecular ion m/z 426 (M + H) with the intensity of the corresponding ion from trideuterated internal standard, m/z 429 (M + H). Flame-ionization detection was used for the assay of urine samples. The peak height ratio of trimethylated veralipride over trimethylated sulpiride, the internal standard, was used for quantitation of urine samples. A relative standard deviation of less than 10% was found when quantifying 10 ng/ml veralipride in plasma or 1 microgram/ml in urine.

High-performance liquid chromatographic assay of 6-methylthioguanine, a major metabolite of 6-thioguanine, in urine

A flow-fluorimetric high-performance liquid chromatographic assay for 6-methylthioguanine in urine has been developed. This compound is a major catabolite of 6-thioguanine, an important drug in cancer chemotherapy. The metabolite was extracted from alkaline urine with ethyl acetate which was injected onto a reversed-phase high-performance liquid chromatographic system for separation and detection. The method is simple, rapid and sensitive to below 500 ng ml-1 which is below the levels encountered following a therapeutic dose of 6-thioguanine. Another metabolite was chromatographically separated from 6-methylthioguanine and partially characterised.

Characterization of insulin regulation of lipid synthesis in MCF-7 human breast cancer cells

Stimulation of lipid synthesis by insulin in MCF-7 human breast cancer cells is characterized by an increase in acetate incorporation into long-chain fatty acids. The effects occurs in the absence of an increase in glucose uptake by the cells, and cannot be explained by a decrease in turnover of cellular fatty acids. Differential substrate experiments as well as direct measurement of enzyme activities indicate that insulin stimulates increases in activity of the first enzyme of the de novo pathway, acetyl CoA carboxylase. [32Pi] incorporation into phospholipids is also stimulated by insulin. Thin layer chromatography reveals five peaks of [32Pi]-labeled phospholipids corresponding in mobility to the following standards: lysophosphatidylcholine, sphingomyelin, phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine. [32Pi] incorporation into each of these peaks is stimulated, although the degree of stimulation varies.

Enzyme-induced aziridine formation by rat liver microsomes

The metabolic reaction of 2-chloroethylaminobenzoquinone derivatives with rat liver microsomes was studied. In buffer solution containing cellular macromolecules such as DNA or protein, 2-chloroethylaminobenzoquinones were usually stable and could be recovered quantitatively after an appropriate period of incubation. However, in microsomal solution, they were gradually converted into aziridinobenzoquinones via elimination of hydrogen chloride by NADPH-dependent enzyme action. Based on the study of the enzymatic cyclization reaction of 4-chlorobutylaminonaphthoquinone, we concluded that the hydroquinone derivative is an important intermediate for aziridine formation.

Analysis of hydroxylated and demethylated metabolites of mephenytoin in man and laboratory animals using gas-liquid chromatography and high-performance liquid chromatography

Separation of urinary mephenytoin metabolites was evaluated under various gas-liquid chromatographic (GLC) and high-performance liquid chromatographic (HPLC) conditions. A simple and rapid alkylation procedure is described for GLC-using a nitrogen sensitive thermionic detector. The in situ formation of sodium methinylsulfinylmethide is used as base for the perpropylation of hydantoins and their metabolites. Normal-and reversed-phase HPLC of the underivatized compounds was performed using four different types of stationary phases. None of the GLC systems separated all the six hydantoin compounds tested, whereas, normal-and reversed-phase HPLC were able to obtain a complete separation of these compounds. The major metabolites of mephenytoin were 5-phenyl-5-ethylhydantoin, 3-methyl-5-(4-hydroxyphenyl)-5-ethylhydantoin and 5-(4-hydroxyphenyl)-5-ethylhydantoin in man, rat, mouse, rabbit, and guinea pig. 3-Methyl-5-phenyl-5-(2-hydroxyethyl)-hydantoin and 3-methyl-5-(3-hydroxyphenyl)-5-ethylhydantoin are major metabolites in the dog.

Analysis of barbiturates by gas chromatography

This review surveys the evolution of gas chromatographic procedures for the quantification of barbiturates as either the free acids or their derivatives obtained by direct and on-column reactions. Among the aspects discussed, some emphasis is placed on recognized and other sources of interference encountered during analyses.

Chronic anticonvulsive therapy, peripheral nerve conduction velocity, and EMG

Chronic, mentally subnormal epileptic patients were clinically and neurophysiologically studied in order to determine the occurrence and type of peripheral nerve dysfunction. We observed significant impairment of motor and sensory nerve conduction velocities and H-reflex latencies. Amplitudes of sensory and motor responses were diminished. Motor distal latencies were not prolonged. Conclusive EMG signs of active denervation were not observed. The possible role of anticonvulsive treatment as an underlying noxa is discussed.

Anion mass spectrometry of barbiturates

Recent trends towards increasing abuse of the barbiturates has led to a proposal to legally restrict some of them. The implementation of the resulting legislation might require specific identification of the barbiturates. Such identification is not readily available from electron impact mass spectra and, even when these are supplemented with chemical ionization data, barbiturates differing only in isomeric sidechains are not completely characterized. In this study the anion mass spectra of 30 barbiturates, including all of those commonly available, are presented. The spectra are simple; ions arising from hydrogen atom and sidechain elimination from the initially formed [M]- ion are diagnostic of the barbiturate. For all but two of the barbiturates (butalbital and idobutal) relative peak intensities will discriminate between barbiturates differing only in isomeric sidechains.

A rapid and simple method for the esterification of fatty acids and steroid carboxylic acids prior to gas-liquid chromatography

A simple procedure for the esterification of steroid carboxylic acid groups using an acetyl chloride/alcohol reagent has been carefully evaluated. The ease with which these esters can be formed using this reagent depends on the acid and the ester required. C24 bile acids form methyl esters using acetyl chloride/methanol (1:20, v/v) almost instantaneously at 50 degrees C, whereas the C20 aetienic acid studied requires 2 h at 50 degrees C. The formation of isopropyl esters of 5 beta-cholanic acid takes longer (4 h at 50 degrees C) than the formation of n-propyl esters (1 h at 50 degrees C). The identity of various esters fo cholanic acids formed using this reagent have been checked by gas chromatography-mass spectrometry and various other procedures used for the methylation of fatty acids have been examined to establish whether they can be used for the quantitative esterification of bile acids.

Determination of barbiturates in mouse tissues by high-performance liquid chromatography

Procedures for determining barbiturates in mouse tissues were investigated. High-performance liquid chromatography (HPLC) with mixtures of water and methanol as the mobile phase and muBondapak C18 as the stationary phase is superior to gas and thin-layer chromatography with respect to ease of sample preparation, accuracy, sensitivity and time required for analysis. The first step in the analysis, the extraction of barbiturates from tissues, was also investigated and good recoveries were achieved. The time courses of barbiturate concentrations in mouse brain, kidneys and liver after oral administration of barbiturate-beta-cyclodextrin complex to mice were determined by HPLC using UV detection at 210 nm.

Plasma levels of diphenylhydantoin and the control of adult epileptic seizures: a Chilean experience

In a prospective study of 117 adult ambulatory patients, 110 of whom were epileptics treated only with oral diphenylhydantoin (DPH), plasma levels of this drug were determined by gas-liquid chromatography. The average follow-up time was 6 months (range, 3 to 13 months); satisfactory control of seizures was obtained with plasma levels in the 10.2 to 25.8 micrograms/ml range, representing 68% of the patients whose seizures had been controlled. The dosage received by this group was from 4.2 to 6 mg/kg, with an average of 5.1. In general, these results agree with those found in European or North American patients, even though some differences or little clarity in the methodology of other trials make comparison difficult. This similarity of results makes one think that genetic or environmental differences do not alter the response to DPH in our patients, but further studies are necessary in that area. This paper can serve as a basis for the extrapolation of data about DPH coming from other latitudes that have been considered supposedly valid for Latin American epileptic patients.

Gas chromatographic determination with flash methylation of palmitic acid in amniotic fluid in prediction of fetal lung maturity

A new method for determination of palmitic acid in amniotic fluid was developed. The dipalmitoyl lecithin was hydrolysed, and after extraction the palmitic acid was flash methylated in the injector of the gas chromatograph. The between batch coefficient of variation was 6.0% at 40 and 70 mumol/l of palmitic acid concentrations in 500 microliters amniotic fluid. The accuracy of the method was demonstrated by linearity, recovery and correlation studies. The correlation coefficient was 0.98 between the new and bortrifluoride methylating method. The concentrations of lecithin and palmitic acid in amniotic fluid showed a correlation coefficient of 0.97. If the concentration of palmitic acid falls below 80 mumol/l respiration distress syndrome is likely. The new method was simple and easy to carry out and could be adjusted for haemoglobin contamination of the amniotic fluid. It was concluded that the determination of palmitic acid in amniotic fluid was a reliable method for the assessment of fetal lung maturity that could replace the determination of lecithin concentration.

Quantitative flash-methylation analysis of phenobarbital

In phenobarbital measurement by GLC with the flash-methylation technique, using trimethylanilinium hydroxide as a methylating reagent, a small amount of water decomposed phenobarbital and interfered with the quantitative analysis. Thus, both the sample and the methylating reagent must be sufficiently dehydrated to attain quantitative analyses. The hydrolysis decomposition product of phenobarbital was N-methyl-2-phenylbutyramide, as shown by its mass spectrum. The sum of methylated phenobarbital and N-methyl-2-phenylbutyramide (if observed in the spectrum) can be used for an accurate phenobarbital assay in the present flash-methylation technique.

In vivo studied on the metabolism of dibenzo [c,f]-[1,2] diazepine

The in vivo metabolism of dibenzo [c,f]-[1,2] diazepine (I) was studied after i.p. administration to rats, in order to observe the influence of the heteroatom on the metabolic pathway. Metabolites were separated by chromatography and their structures elucidated by mass spectrometry, by both gas chromatography coupled with mass spectrometry and the direct inlet system. Six metabolites were identified, some of them by direct comparison with authentic samples.