Glass capillary gas chromatography with electron-capture detection. Separation of prostaglandins

Glass capillary gas chromatography of the prostaglandins was performed on a system including an all-glass, solventless injector; thermostable methylphenyl-polysiloxane glass capillary columns; and a conventional electron-capture detector fitted with a make-up gas tee. The principal stable metabolites of prostaglandin endoperoxide were separated as perfluorinated derivatives in 35 min. Detection limits equal or exceed those obtained for packed column separations and electron capture detection. Prostaglandin endoperoxide metabolic profiles from mammalian cell cultures were obtained using this system. These profiling studies are not possible with other chromatographic methods because of inferior resolution and sensitivity.     

Simultaneous determination of nitroglycerin and its dinitrate metabolites by capillary gas chromatography with electron-capture detection

A sensitive gas chromatographic-electron-capture detection method for the simultaneous determination of the antianginal drug nitroglycerin (GTN) and its dinitrate metabolites (1,2-GDN and 1,3-GDN) was developed. Human plasma samples (1 ml) spiked with 2,6-dinitrotoluene as the internal standard were extracted once with 10 ml of a methylene chloride-pentane mixture (3:7, v/v). Using this solvent system, less contaminants are extracted into the organic phase from plasma, resulting in cleaner chromatograms and prolonged column life. A break point was observed on the standard curves of GTN and GDNs. The two linear regions for the detectable concentrations of GTN are 0.025-0.3 and 0.3-3 ng/ml and for 1,2-GDN and 1,3-GDN they are 0.1-1 and 1-10 ng/ml. The limits of detection by this method for GTN, 1,2-GDN and 1,3-GDN in plasma are 0.025, 0.1 and 0.1 ng/ml, respectively.     

Quantitative analysis of prostaglandins in cell culture medium by high-resolution gas chromatography with electron-capture detection

Prostaglandins have been shown to be important modulators of haemostatis , immune responses, and growth of normal and neoplastic cells. In order to investigate the cell origin and metabolic profile of the endogenous prostaglandins in human tumours, a convenient extraction and gas chromatographic method for measuring the various classes of prostaglandins was developed. Infiltrating macrophages from human tumours were isolated using adherence to plastic. Macrophage-enriched and macrophage-depleted cell populations were then cultured in vitro and the media supernatant was studied for the presence of prostaglandins E1, E2, F2 alpha, and 6-keto-F1 alpha (the spontaneous breakdown product of prostacyclin, PGI2). Routinely, 1 ml of medium containing 10(6) cells was studied. The eicosanoids were extracted using commercially available octadecylsilyl silica reversed-phase columns prior to derivatization. Standards and samples were prepared as pentafluorobenzyl ester (methoxime) trimethylsilyl ether derivatives for analysis on an OV-101 (25 m X 0.2 mm) fused-silica capillary column. Recovery of standards ranged from 93% to 37%, with linear recovery in all instances (regression coefficients greater than 0.98). Detection limits were 20 pg for each of the prostaglandins. Analysis of cell subpopulations from six human tumours revealed that infiltrating macrophages produce various prostaglandin profiles and are largely responsible for the prostaglandin production in human cancer. The described analytical method is the first application of high-resolution gas chromatography with electron-capture detection to the quantitative profiling of prostaglandins from human cell culture.     

Quantitative determination of nitroglycerin in human plasma by capillary gas chromatography with electron-capture detection

A sensitive method for the selective determination of nitroglycerin at concentrations down to 50 pg/ml in human plasma is described. After the addition to plasma of a known amount of butane-1,2,4-triol trinitrate as internal standard, both compounds are extracted into hexane. Nitroglycerin is then quantitated by capillary gas chromatography with electron-capture detection.     

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.     

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 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.     

Specific assay for unconjugated dehydroepiandrosterone in human plasma by capillary gas chromatography with electron-capture detection.

A specific and sensitive method for the determination of unconjugated dehydroepiandrosterone in plasma is described. After extraction and purification of the extracts on a Celite column, the iodomethyldimethylsilyl ether derivative of dehydroepiandrosterone was isolated on an aluminium oxide column and assayed by gas chromatography with electron-capture detection. The method is sensitive: sample volumes of 0.5-1 ml are sufficient for the determination of dehydroepiandrosterone in plasma of normal male and female subjects aged 1-80 years. The assay is highly specific and has the potential to be used as a reference method for the determination of unconjugated dehydroepiandrosterone in biological samples.