Determination of xylometazoline in plasma and urine by gas chromatography using a fused-silica capillary column and an electron-capture detector

A sensitive method is described for the determination of unchanged xylometazoline in plasma and urine at concentrations down to 35 nmol/l. After addition of naphazoline as an internal standard, both compounds are extracted with dichloromethane-diethyl ether (20:80) at pH 10, back-extracted with an acidic solution and re-extracted from a sodium hydroxide solution with dichloromethane-diethyl ether (20:80). The compounds are then derivatized with heptafluorobutyric anhydride in the presence of pyridine. The derivatives are determined by capillary gas chromatography using electron-capture detection.     

Determination of propafenone in biological fluids by fused-silica capillary gas chromatography using electron-capture detection

A gas-liquid chromatographic method with electron-capture detection using a capillary column with the inlet in the splitless injection mode is reported for the assay of propafenone. A 25 m X 0.31 mm cross-linked, 5% phenylmethylsilicone-coated fused-silica capillary column was employed for all analyses. The present method provides improved selectivity and sensitivity over other existing gas chromatographic and high-performance liquid chromatographic (HPLC) methods. Linearity was observed in the ranges 2.5-50 and 10-100 ng/ml. The coefficient of variation was found to be less than 10% over the concentration ranges studied. Application of the developed method is demonstrated by measuring serum propafenone concentrations over 24 h in a normal healthy volunteer after a single oral dose of propafenone and by measuring trough plasma propafenone concentrations at steady state in patients receiving this new antiarrhythmic drug. Validity of the present method is further demonstrated by comparison of analytical results obtained from measurement of patient samples using a modified published HPLC method.     

Determination of busulfan in human plasma by gas chromatography with electron-capture detection

A simple and highly sensitive gas chromatographic method has been developed for the determination of busulfan in human plasma. After extraction of plasma specimens (clinical or spiked) with ethyl acetate, busulfan and the internal standard [1,8-bis(methanesulfonyloxy)octane] were derivatized with 2,3,5,6-tetrafluorothiophenol to yield compounds monitored by a 63Ni electron-capture detector. Sample recoveries from extraction and derivatization were greater than 78 and 91%, respectively. The limit of quantitation was 0.01 microgram/ml (0.04 microM) in 1 ml of plasma with a linear relationship over the 0.01-1.0 micrograms/ml (0.04-4 microM) concentration range. The method has been applied to analyze the plasma versus time profile of busulfan in human subjects following administration of an oral dose of 4 mg/kg per day as a marrow ablative chemotherapy for bone marrow transplantation.     

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 x 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 approximately 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 amount is approximately 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 4-hydroxyandrostenedione in plasma and urine by extractive alkylation and electron-capture gas chromatography

A sensitive and specific quantitative assay has been developed for the determination of 4-hydroxyandrostenedione (4-OHA), a potent aromatase inhibitor used in the treatment of estrogen-dependent breast cancer. This steroid has a high first-pass metabolism and is extensively metabolized, mainly by glucuronidation. Plasma levels of unchanged 4-OHA are very low, even after high peroral doses. The analytical method is based on the addition of 17 alpha-ethinylestradiol (internal standard), liquid-liquid extraction from biological material followed by extractive alkylation with pentafluorobenzyl bromide and quantitation by gas chromatography. The method has been validated for sensitivity, accuracy and precision and was found to be suitable for application to pharmacokinetic and bioavailability studies of peroral formulations of 4-OHA.     

Use of deactivated fused-silica capillary precolumns in pesticide analysis by gas chromatography with electron-capture detection.

The advantages and disadvantages of coupling a retention gap of fused-silica between the injection port and the chromatographic column are discussed. The influence on the peak width and height of several factors such as the solvent (n-hexane, acetone, ethyl acetate and methanol), the gap (length, inner diameter, deactivation mode), the injection volume and the pesticide concentration has been examined. Those factors have very different incidences so, it is not possible to extract a general recommendation about the use of gaps. For this reason, checking its viability in each particular case is more advisable.     

Determination of the S(+)- and R(-)-enantiomers of baclofen in plasma and urine by gas chromatography using a chiral fused-silica capillary column and an electron-capture detector

A sensitive and enantiospecific gas chromatographic method for the determination of the S(+)- and R(-)-enantiomers of baclofen (I and II) in plasma and urine has been developed and validated. The method is based on the complete resolution of the derivatized enantiomers on a chiral fused-silica capillary column. The hydrochloride salt of a (-)-fluoro analogue of baclofen (III.HCl) was used as the internal standard in plasma, the hydrochloride salt of a (+)-fluoro analogue of baclofen (IV.HCl) as the internal standard in urine. Rapid and convenient isolation of the compounds was achieved using reversed-phase Bond-Elut C18 columns. After elution, the compounds were converted into isobutyl esters and purified by base-specific solvent extraction. The isobutyl esters were then N-acylated with heptafluorobutyric anhydride. The derivatives were quantitated after separation on the chiral column using electron-capture detection. The analysis of spiked plasma and urine samples demonstrated the good accuracy and precision of the method, with limits of quantitation of 25 nmol/l for I and II in plasma and of 2 mumol/l for I and II in urine. The method appears to be suitable for use in pharmacokinetic studies of the enantiomers in plasma and urine from animals and man after administration of the racemic baclofen.     

Determination of the GABAergic antidepressant drug fengabine and some of its metabolites in plasma by capillary gas chromatography with electron-capture detection

A sensitive capillary gas chromatographic method was developed for the determination of fengabine (a GABAergic antidepressant drug) and some of its metabolites in plasma samples. The method involves a single and rapid liquid-liquid extraction of the parent drug and metabolites from plasma buffered at pH 5, evaporation of the organic phase under nitrogen, derivatization to tert.-butyldimethylsilyl ethers and esters and automatic gas chromatography on a fused-silica, silicone-bonded capillary column coupled to an electron-capture detector. The detection limit for fengabine and other compounds is lower than 1 ng/ml in plasma; the method was successfully applied to pharmacokinetic and drug monitoring clinical studies and tested on more than 2000 biological samples and was found not to suffer from endogenous or exogenous interferences.     

Determination of fluvalinate residues in beeswax by gas chromatography with electron-capture detection

A simple, rapid, and accurate method is described for the determination of residual fluvalinate in beeswax. The procedure consists of partitioning on a disposable column of diatomaceous earth (Extrelut), followed by chromatographic cleanup on a Florisil cartridge. The final extract is analyzed by capillary gas chromatography with electron-capture detection (GC-ECD). Briefly, wax samples were dissolved in n-hexane, and the solutions were sonicated and transferred to Extrelut columns. The fluvalinate was extracted with acetonitrile, and a portion of the extract was cleaned up on a Florisil cartridge. The fluvalinate was eluted with diethyl ether-n-hexane (1 + 1) and directly determined by GC-ECD. Recoveries from wax samples spiked at 5 fortification levels (100-1500 microg/kg) ranged from 77.4 to 87.3%, with coefficients of variation of 5.12-8.31%. The overall recovery of the method was 81.4 +/- 3.2%, and the limit of determination was 100 microg/kg.     

Determination of pesticide residues in lettuce by gas chromatography with electron-capture detection

A sensitive, rapid, and simple multiresidue method for the simultaneous determination of 19 pesticides in different varieties of lettuce (Lactuca sativum) was developed. Lettuce samples were extracted by homogenization with acetone and partitioned into ethyl acetate-cyclohexane. Subsequent sample cleanup was not needed. Final determination was made by capillary gas chromatography (GC) with electron-capture detection (ECD). Confirmation analysis of pesticides was performed by GC coupled with mass spectrometry in the selected ion monitoring mode. The average recovery by the GC-ECD method obtained for these compounds varied from 66.4 to 119.2% with relative standard deviations < 7.7%. The GC-ECD method has good linearity, and the detection limit for the pesticides studied varied from 0.1 to 3.8 microg/kg. The proposed method was used to determine pesticide levels in different types of lettuce grown in soils from experimental fields.