Determination of ritodrine in biological fluids of the pregnant sheep by fused-silica capillary gas chromatography using electron-capture detection

A sensitive and selective gas chromatographic assay method employing splitless injection, fused-silica capillary columns and electron-capture detection is reported for the quantitation of the tocolytic drug, ritodrine, in a variety of biological fluids obtained from the pregnant ewe and fetus. This method has improved sensitivity and selectivity over previously published assay procedures. A 25 m × 0.31 mm I.D., cross-linked 5% phenylmethylsilicone, fused-silica capillary column was employed for all analyses. Linearity of response was observed over the range 2.5–75 ng of ritodrine base per 0.05–0.5 ml of biological fluid, representing ≈ 1–75 pg at the detector. The coefficient of variation was less than 10% over the range 2.5–75 ng of added ritodrine. The minimum quantifiable amounts is ≈ 2.5 ng from a 0.5-ml biological fluid sample. Applicability of this method to biological fluids, obtained from ovine subjects, is demonstrated by the analysis of samples obtained during the course of ritodrine placental transfer studies.     

Determination of delta-aminolaevulinic acid in biological fluids by gas-liquid chromatography with electron-capture detection

A derivative of delta-aminolaevulinic acid (AmLev), 2-methyl-3-acetyl-4-(3-propionic acid pentafluorobenzyl ester)pyrrole, with favourable properties for g.l.c. with electron-capture detection, was synthesized. Less than 1 pg could be detected on the column. 6-Amino-5-oxohexanoic acid formed the analogous derivative under similar conditions and was used as the internal standard in the development of a highly sensitive and specific assay for AmLev. The method has been applied to peripheral-venous and umbilical-cord plasma and to cerebrospinal fluid of normal and porphyric subjects.     

Determination of acetaldehyde in biological samples by gas chromatography with electron-capture detection

A simple specific assay was developed for the determination of acetaldehyde in biological samples. Acetaldehyde was derivatized to 2,4-dinitrophenylhydrazone, which was determined by gas chromatography with electron-capture detection. The use of this detection method is an important device to which no one drew notice. This procedure was very simple and so sensitive that as little as 500 fmol of acetaldehyde could be measured in aqueous solution. The calibration curve of acetaldehyde was linear at least up to 40 μM. Its recoveries from human plasma and rat liver homogenate were 96.5 and 95.7%, respectively.     

Determination of triazolam in serum by deactivated metal capillary gas chromatography with electron-capture detection

A method for the determination of trace amounts of triazolam in serum by deactivated metal capillary gas chromatography with electron-capture detection was established. The column used exhibits excellent thermostability in high-temperature analysis and easy handling and a long lifetime of the column and well shaped peaks on the chromatograms are obtained. With the metal capillary column, it was found to be easier to maintain suitable analytical conditions for the routine assay of triazolam than with a fused-silica column. With this method, 0.5 ng/ml of triazolam in serum can be determined. The method is useful for pharmacokinetic and therapeutic purposes.     

Analysis of malondialdehyde in biological matrices by capillary gas chromatography with electron-capture detection and mass spectrometry

A gas chromatographic method is described for the quantification of free and total malondialdehyde (MDA) in biological materials. The procedure involves derivatization of the analyte with 2,4,6-trichlorophenylhydrazine, extraction with n-hexane, and separation of the cyclic derivatization product on a OV-5 gas chromatographic column. Concentration of the derivatization reagent, pH, reaction time, and temperature were investigated to determine the optimal derivatization conditions. Under these conditions, the method allows for the selective detection of free and total MDA at femtomole levels in several biological materials without any interferences. The procedure yields relative standard deviation values for the intra- and interassays in the range 3.3 and 3.9%, respectively, for the electron-capture and mass-selective (SIM mode) detection systems. Recoveries of MDA from spiked matrices reached 96%. The present method offers the advantage of the alternative use of either electron-capture or mass-selective detection. Furthermore it avoids overestimation of MDA since it employs mild conditions for sample processing and there is no need for preventing protein separation for the assessment of free MDA.     

Determination of 3-hydroxy-guanfacine in biological fluids by electron-capture gas—liquid chromatography

An electron-capture gas—liquid chromatographic method was developed for measuring 3-hydroxy-guanfacine, the main metabolite of guanfacine in human plasma and urine. After extraction, the metabolite was derivatized by condensing the amidino group with hexafluoroacetylacetone and by methylating the NH and OH groups with methyl iodide. The obtained derivative possessed good bioanalytical gas chromatographic properties, using a capillary column. The O-glucuronide was measured after enzymatic hydrolysis. Unchanged guanfacine could be determined in urine together with its 3-hydroxy metabolite by this method.     

Determination of paroxetine levels in human plasma using gas chromatography with electron-capture detection

A simple, rapid and sensitive procedure using gas chromatography with electron-capture detection to measure paroxetine levels in human plasma has been developed. The analyte was extracted from plasma with ethyl acetate after basification of the plasma and then derivatized with heptafluorobutyric anhydride before gas chromatographic separation. The calibration curves were linear, with typical r² values >0.99. The assay was highly reproducible and gave peaks with excellent chromatographic properties.     

Determination of remifentanil in human blood by capillary gas chromatography with nitrogen-selective detection

A validated method for the determination of remifentanil in human blood, applicable to all therapeutic concentrations, using capillary GC with nitrogen-specific detection and fentanyl as the internal standard has been developed. Citrated whole blood samples were extracted into 1-chlorobutane following precipitation of proteins with methanol. The drugs were back extracted into 10 mM HCl and re-extracted into methanol-1-chlorobutane. The extracts were reconstituted in methanol and injected onto a 25-m BPX-5 column. The lower limit of quantitation was 0.2 ng/ml with within- and between-day coefficients of variation of less than 15%.     

Determination of gamma-hydroxybutyric acid in biological fluids by using capillary electrophoresis with indirect detection

gamma-Hydroxybutyric acid (GHB) is a central nervous system (CNS) depressant and hypnotic which, in recent times, has shown an increasing abuse either as recreational drug (due to its euphoric effects and ability to reduce inhibitions) or as doping agent (enhancer of muscle growth). Analogues of GHB, namely gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD), share its biological activity and are rapidly converted in vivo into GHB. At present, GHB and analogues are placed in the Schedules of Controlled Substances. Numerous intoxications in GHB abusers have been reported with depressive effects, seizures, coma and possibly death. The purpose of the present work was the development of a rapid analytical method based on capillary zone electrophoresis for the direct determination of GHB in human urine and serum at potentially toxic concentrations. Analytical conditions were as follows. Capillary: length 40 cm (to detector), 75 microm i.d.; buffer: 5.0 mM Na(2)HPO(4), 15 mM sodium barbital adjusted to pH 12 with 1.0 M NaOH; voltage: 25 kV at 23 degrees C; indirect UV detection at 214 nm; injection by application of 0.5 psi for 5 s. alpha-Hydroxyisobutyric acid was used as internal standard (IS). Sample pretreatment was limited to 1:8 dilution. Under these conditions, the sensitivity was approximately 3.0 microg/ml (signal-to-noise ratio >3). Calibration curves prepared in water, urine and serum were linear over concentration ranges 25-500 microg/ml with R(2)>/=0.998. Analytical precision was fairly good with R.S.D.<0.60% (including intraday and day-to-day tests). Quantitative precision in both intraday and day-to-day experiments was also very satisfactory with R.S.D.相似文献   

Analysis of pipecolic acid in biological fluids using capillary gas chromatography with electron-capture detection and [H11]pipecolic acid as internal standard

A sensitive and accurate stable isotope dilution assay was developed for the measurement of pipecolic acid in body fluids using capillary gas chromatography with electron-capture detection. The method utilizes [²H₁₁]pipecolic acid as the internal standard. Sample preparation consisted of derivatization in aqueous solution (pH 11.5) of the amine moiety with methyl chloroformate to the N-methylcarbamate, followed by acidic ethyl acetate extraction at pH ≤ 2 and further derivatization of the carboxyl moiety with pentafluorobenzyl bromide, the excess of which was removed by solid-phase extraction. Control values have been determined in the plasma of at-term infants, age > 1 week (n = 21, mean = 1.36 μM, range = 0.47–3.27 μM). The utility of the method was demonstrated by quantitating pipecolic acid in biological fluids derived from patients with peroxisomal disorders. The method was validated against an established electron-capture negative ion mass fragmentographic technique.     

Quantitation of levorphanol in human plasma at subnanogram per milliliter levels using capillary gas chromatography with electron-capture detection

A gas chromatographic method for the determination of levorphanol in human plasma is described. The method utilizes extractive alkylation with tetrabutylammonium cation as the phase-transfer catalyst and pentafluorobenzyl bromide as the alkylating agent, and employs a structural analog, d-3-hydroxy-N-ethylmorphinan, as the internal standard. The pentafluorobenzyl ethers formed are separated by capillary gas chromatography and detected by electron capture. The method has good precision and accuracy for concentrations ranging from 0.25 ng/ml to 100 ng/ml and has been used to measure plasma concentrations as part of a study to evaluate the management of chronic neuropathic pain with levorphanol.     

Assay of timolol in human plasma using gas chromatography with electron-capture detection

A simple and sensitive gas chromatographic method has been developed for the determination of timolol in plasma using electron-capture detection and propranolol as internal standard. Timolol was extracted using butyl chloride and derivatized using trifluoroacetic anhydride in butyl acetate. The lower detection limit for the assay was found to be 1 ng/ml from 1 ml of plasma. Extracted standards gave within-day precision of 12.55, 9.68 and 3.78% for 1, 20 and 100 ng/ml plasma samples, respectively. A recovery of at least 80% of timolol was found using the extraction method described. The assay was used in a randomized cross-over bioequivalence trial using an oral administration of 20 mg of timolol. Pharmacokinetic parameters compare favourably with other literature values.     

Determination of fosfomycin in biological fluids by capillary electrophoresis

A capillary electrophoresis method was developed for the determination of the antibiotic fosfomycin in serum, cerebrospinal fluid and aqueous humor. The technique uses indirect UV detection and the working buffer includes an organic cation to improve fosfomycin mobility. The electrophoretic time of migration is less than 7 min in both fluids. The limit of quantification is 2.5 and 1 μg/ml in serum and aqueous fluids, respectively (signal-to-noise RATIO = 3). The method was validated in serum and water over the concentration range 2.5–200 μg/ml. The calibration graph for serum was linear with a correlation coefficient r = 0.999. At a fosfomycin concentration of 2.5 μg/ml in serum, the intra- and inter-day precisions (coefficients of variation) were 5 and 5.2%, respectively. The mean recovery in serum was 94.5% (S.D. = 2.4%).     

Determination of urinary methylhistamine excretion in male and female rats by gas chromatography with electron-capture detection

A gas-liquid chromatographic method for the determination of methylhistamine in urine is described. Methylhistamine is reacted with 2,6-dinitro-4-trifluoromethylbenzene sulfonic acid and the derivative thus formed is quantitated with electron-capture detection. The twenty-four hour urinary excretion of methylhistamine in the male rat is about five-fold greater than that in the female rat. Amino-guanadine, a diamine oxidase inhibitor, causes a four-to five-fold increase in methylhistamine excretion in both male and female rats. Treatment with pargyline, a monoamine oxidase inhibitor, causes only a small increase in methylhistamine excretion in male and female rats thereby suggesting that oxidative deamination of methylhistamine is a relatively minor pathway.