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 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 the (+)- and (-)-enantiomers of pirprofen in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed to determine the (+)- and (-)-enantiomers of pirprofen, an anti-inflammatory drug. After addition of an internal standard, the plasma sample was brought onto a glass column pre-packed with silica and eluted with dichloromethane. The extracts were derivatized with 1,1'-carbonyldiimidazole and R (+)-1-methylbenzylamine to form the two diastereomeric amides. The diastereoisomers were separated on a chiral column by HPLC with ultraviolet detection at 272 nm using n-hexane-dichloromethane (64:36, v/v) as the mobile phase. The limit of quantitation was 0.992 mumol/l (0.25 microgram/ml) for each enantiomer.     

Determination of nifedipine and its three principal metabolites in plasma and urine by automated electron-capture capillary gas chromatography

A sensitive, efficient, linear and reproducible capillary gas chromatographic method with electron-capture detection was developed for the quantitation of nifedipine and its primary metabolite M-I in plasma together with the urinary and principal metabolites M-II and M-III. On-column, rather than split-splitless, injection was employed to obviate oxidative degradation of nifedipine to M-I. The photosensitivity of nifedipine was re-examined under laboratory conditions and nifedipine was found to have a half-life in excess of two days when amber glassware and darkroom manipulations under red light were used. The method can determine nifedipine and its metabolites in plasma and urine after a single oral dose of 5 mg and can be applied to measure M-I production by human liver microsomes.     

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.     

Analysis of lipopolysaccharides by methanolysis, trifluoroacetylation, and gas chromatography on a fused-silica capillary column

A gas chromatographic method for simultaneous analysis of fatty acids and sugars of lipopolysaccharides (LPS) has been developed. The sample (1 mg or less) is methanolyzed at 85°C overnight in 2 M HCl in methanol. The released methyl esters and methyl glycosides are trifluoroacetylated and chromatographed on a methylsilicone-impregnated fused-silica capillary column. This column resolves all ordinary LPS sugars and fatty acids, and quantitative analysis is possible, including 2-deto-3-deoxyoctanoic acid (KDO), glucosamine and heptoses. 3,6-Dideoxyhexoses show some thermal degradation at 85°C during methanolysis, but this can be overcome by lowering the temperature to 37°C. For KDO the higher temperature similarly causes some degradation, but a reproducile response factor was found. The method appears to be useful for analysis of purified LPS as well as a means for monitoring for LPS content during purification of bacterial antigents of different kinds.     

Determination of amino acids by gas chromatography using a wide bore capillary column

A procedure is described in which a wide bore capillary column is used as an alternative to the more traditional packed column for the quantitative analysis of amino acids as their N-heptafluorobutyryl isobutyl ester (HBB) derivatives. The column, installed in a gas chromatograph previously configured for use with a packed column, is shown to give good reproducibility by repeated determination of amino acid response factors (RSD values for all amino acids are below 3%). A number of problems, encountered during the use of this column, are discussed and suitable techniques to overcome them are reported.