Automated determination of nifedipine in human plasma by capillary gas chromatography with electron capture detection

A rapid, sensitive, and reliable method for the determination of nifedipine in human plasma is described. Using a single-step solvent extraction and capillary gas chromatography combined with electron capture detection, an assay sensitivity of 2 ng/ml is achieved routinely using 0.5 ml of plasma. Intact nifedipine is quantitated and separated from its nitroso- and nitropyridine-derivatives. The suitability of the assay for pharmacokinetic studies is illustrated.     

Nanogram level quantitation of oxycodone in human plasma by capillary gas chromatography using nitrogen-phosphorus selective detection.

A sensitive and specific capillary gas chromatographic assay is reported for the quantitation of oxycodone in human plasma. The technique involves a single extraction of oxycodone and internal standard (hydrocodone) from plasma by toluene containing 1% isopropanol. Separation is achieved on a methyl silicone (HP-1) fused-silica capillary column (25 m x 0.2 mm I.D., 0.33 microns film thickness) and detection is by nitrogen-phosphorus selective mode. The minimum quantifiable limit is 1.8 ng/ml using 2 ml of plasma. The method is applicable to characterize the plasma profile of oxycodone in humans after a single oral 5-mg oxycodone hydrochloride tablet.     

Determination of bencyclane in human plasma by means of capillary gas chromatography and nitrogen-phosphorus selective detection

A sensitive and specific method for the determination of bencyclane in human plasma is presented. Bencyclane was extracted from human plasma with two 3-ml volumes of isooctane and was shaken for 10 min. The organic phase was separated and evaporated to dryness at 40 degrees C under a nitrogen stream. The residue was dissolved and an aliquot was injected into the gas chromatograph. The separation was performed with a DB-17 column with helium as the carrier gas. Nitrogen-selective detection was performed. The quantification was performed with the signal output. The limit of detection was 1 ng/ml.     

Automated high-performance liquid chromatographic method for the determination of mianserin in plasma using electrochemical detection.

An automated high-performance liquid chromatographic method for the determination of mianserin in plasma is described. Extraction and injection of the samples were automatically done by the Gilson ASPEC system using C8, 100-mg Supelclean solid-phase extraction columns. The extracts were chromatographed on a reversed-phase C18 column (150 mm x 3.9 mm I.D.) with a phosphate buffer-acetonitrile-methanol mobile phase and the analytes detected electrochemically. Calibration curves were linear to at least 53.7 ng/ml at which the between-day relative standard deviation was 5% and the recovery 101%. The limit of quantification was 1.67 ng/ml at which the between-day relative standard deviation was 9% and the recovery 92% using a sample volume of 0.5 ml. The method was applied to the determination of mianserin in the plasma of normal human volunteers participating in a comparative bioavailability study.     

Determination of fendiline in human plasma by means of capillary gas chromatography and nitrogen-phosphorus selective detection.

A sensitive and specific method for the determination of fendiline in human plasma is presented. Fendiline was extracted from human plasma after the addition of phosphate buffer two times with 4 ml of n-hexane. The organic phase was separated and evaporated to dryness at 40 degrees C under a stream of nitrogen. The residue was dissolved and an aliquot was injected into the gas chromatograph. Chromatographic separation was performed with a DB-1 column with helium as carrier gas. Nitrogen-selective detection was performed. Quantification was performed with the signal output. The limit of detection was 1 ng/ml of plasma.     

Determination of carphedon in human urine by solid-phase microextraction using capillary gas chromatography with nitrogen-phosphorus detection

Carphedon is a phenyl derivative of nootropil and is effective in increasing physical endurance and cold resistance, and is used for amnesia treatment. Carphedon was extracted from human urine samples by solid-phase microextraction with a 65 microns carbowax-divinylbenzene-coated fiber. This analysis was performed by using capillary gas chromatography with nitrogen-phosphorus detection and optimized at pH 9.6, 30% NaCl, immersion time 10 min and desorption in the GC injector at 250 degrees C for 3 min. The regression equation for carphedon showed good linearity in the range from 0.1 to 10 micrograms ml-1 for human urine samples. The limit of detection was 0.01 microgram ml-1. The developed method is more sensitive and simpler in sample preparation than liquid-liquid extraction and can be applied to doping analysis for stimulants.     

Determination of polyamines in human erythrocytes by capillary gas chromatography with nitrogen-phosphorus detection

A capillary gas chromatographic method with nitrogen-phosphorus detection is used to determine simultaneously 1,3-diaminopropane, putrescine, cadaverine, spermidine and spermine in human erythrocytes. The compounds are isolated by adsorption on silica and converted into their heptafluorobutyryl derivatives. We give quality-control data and (age-dependent) normal values for 48 apparently healthy controls.     

Solid-phase microextraction for the determination of pethidine and methadone in human urine using gas chromatography with nitrogen-phosphorus detection

A simple and rapid analytical method is presented for the determination of pethidine (meperidine) and methadone in human urine using solid-phase microextraction (SPME) and gas chromatography with nitrogen-phosphorus detection (GC-NPD). After the analytes had been partitioned between an extracting phase and the aqueous sample matrix, the needle of the coating fiber assembly was injected directly into the GC injector. The analytes were thermally desorbed in the heated injector (240 degrees C) and subsequently separated and detected by the GC-NPD system. The factors influencing the SPME method, such as the salt (NaCl) effect (15%), pH (pH 11), and equilibration time (30 min), were optimized. The calibration graphs for urine samples showed a good linearity. The detection limit was below 1 ng ml-1 for both drugs.     

High-performance liquid chromatographic determination of nafazatrom in human plasma using fluorescence detection

A rapid, sensitive, and selective high-performance liquid chromatographic assay was developed for determination of the pyrazole derivative nafazatrom (Bay g 6575, NFZ) in human plasma. Separation was obtained using a normal-phase Si-60 column and a mobile phase of methylene chloride--methanol (90:10, v/v) containing 0.25% water. The fluorescence of NFZ was monitored at excitation and emission wavelengths of 232 and 362 nm, respectively. The recovery of NFZ extracted from plasma with methylene chloride was 109 +/- 5% (mean +/- S.D.) in the concentration range from 5.0 to 500 ng/ml. The assay was applied to the determination of plasma concentrations of NFZ following administration of the compound to patients in a Phase I clinical trial.     

Enantioselective gas chromatographic assay with electron-capture detection for dl-ritalinic acid in plasma

Enantioselective gas chromatographic assays for the quantitation of methylphenidate and its major metabolite ritalinic acid in plasma are described. The procedures involved the extraction of methylphenidate enantiomers from alkanised plasma. The plasma was then washed to ensure complete removal of methylphenidate before saturation with sodium carbonate to promote the extraction of ritalinic acid enantiomers with ethyl acetate-isopropanol (60:40) solvent mixture. Subsequently, ritalinic acid enantiomers were converted back into methylphenidate enantiomers by Fisher-Speier esterification. N-Heptafluorobutyryl-L-prolyl chloride, a chiral acylating reagent, was used to convert the enantiomers of methylphenidate into their corresponding diastereomeric amide derivatives, which were separated cleanly on an achiral capillary column (OV-225) and quantitated with electron-capture detection. The assays were sensitive, reliable and reproducible.     

Sensitive assay of methadone in plasma by using capillary gas chromatography with photoionization detection

A new gas chromatographic assay for methadone, utilizing a fused-silica capillary column, is presented. Extreme sensitivity was reached, compared to nitrogen-phosphorus and mass spectrometry detection, by employing a photoionization detector. Plasma concentrations of methadone as low as 1 ng/ml can easily be detected and, by further optimization, 0.1 ng/ml was reached. The minimum detectable amount of methadone reaching the detector was 70 fg. The results indicate that the photoionization detector has potential as a tool in drug monitoring.     

Chiral gas chromatographic assay with flame ionization detection for amphetamine enantiomers in microsomal incubates

A chiral assay for amphetamine enantiomers in rat liver microsomal incubates is based on derivatization with (S)-(-)-N-(trifluoroacetyl)-prolyl chloride (S-TFPC), capillary chromatographic separation of the diastereomeric amide derivatives, and detection by a flame ionization detector. The method is capable of detecting low levels of S- or R-amphetamine. The assay is linear from 5 to 250 micrograms/mL for each enantiomer, and the limit of detection is 0.5 microgram/mL. The analytical method affords the average recoveries of 77.53 +/- 5.22% for R-amphetamine and 74.47 +/- 3.08% for S-amphetamine. The method allows the study of the metabolic depletion of S- and R-amphetamine in rat liver microsomal incubates. The time-dependent concentration of amphetamine enantiomers in rat liver microsomes was determined, and the stereoselectivity of amphetamine phase I metabolism was observed.     

High-performance liquid chromatographic assay for mitoxantrone in plasma using electrochemical detection

A sensitive and specific high-performance liquid chromatographic (HPLC) assay was developed for the quantitation of mitoxantrone in plasma using electrochemical detection. Bisantrene was chosen as the internal standard. A reversed-phase, 10-microns muBondapak C18 analytical column (30 cm X 3.9 mm) with an isocratic mobile phase of 28% acetonitrile in 80 mM sodium formate buffer (pH 3.0) was used. The eluent was monitored by both electrochemical detection at an applied potential of +0.75 V vs. Ag/AgCl and visible absorbance at 660 nm. Only electrochemical detection was able to quantitate the internal standard and provided ten times higher sensitivity than visible absorbance for mitoxantrone with a detection limit as low as 0.1 ng/ml. Calibration curves in the range 0.1-1000 ng/ml showed good linearity (r = 0.998) and precision (coefficient of variation less than 10%). This HPLC method utilized a reproducible and inexpensive liquid-liquid extraction procedure. Using methylene chloride, the extraction efficacy of mitoxantrone from plasma was 85.3% with a coefficient of variation less than 2.1%. This new assay was then applied to measure mitoxantrone concentrations in plasma obtained from two leukemic patients receiving 12 mg/m2 mitoxantrone as a 1-h infusion.