A rapid and sensitive quantitation of Dipterex in serum by solid-phase extraction and gas chromatography with flame thermionic detection

A simple, sensitive, and rapid quantitative method for Dipterex in serum is described. A SepPak C18 cartridge for the extraction and gas chromatography with flame thermionic detection for determination are used. The detection limit is 2.5 ng/mL, and linearity is obtained in the range 5-500 ng/mL.     

The pharmacokinetics of doxylamine: use of automated gas chromatography with nitrogen-phosphorus detection

Sixteen healthy male volunteers received a single oral dose of 25 mg doxylamine succinate. Doxylamine concentrations in plasma were measured by a newly developed gas chromatographic methodology, utilizing direct alkaline extraction into hexane:isoamyl alcohol followed by concentration and autoinjection. Doxylamine kinetics were determined from multiple plasma doxylamine concentrations measured during the 24 hours postdose. Mean kinetic variables were: peak plasma level, 99 ng/mL; time of peak, 2.4 hours postdose; elimination half-life, 10.1 hours; and apparent oral clearance, 217 mL/min. Analogous analytic methodology can be used to study the pharmacokinetics of other drugs of this class.     

Identification and quantification of trihexyphenidyl and its hydroxylated metabolite by gas chromatography with nitrogen-phosphorus detection

A sensitive and specific assay for the simultaneous quantification of trihexyphenidyl and its hydroxylated metabolite in plasma and urine is described. The method is based on the extraction of the drugs with an organic solvent and separation on a 3% OV-17 Chromosorb Q column in a gas chromatograph equipped with a nitrogen-phosphorus detector. The procedure employs SKF 525 A as the internal standard and requires no derivatization. The detection limit was found to be 2 ng/mL for trihexyphenidyl and 1 ng/mL for its metabolite. The precision of the assay procedure for both compounds is about 4 to 7%.     

Retention indices by wide-bore capillary gas chromatography with nitrogen-phosphorus detection

The use of wide-bore capillary columns in gas chromatography (GC) with nitrogen-phosphorus detectors (NPD) is gaining popularity in the toxicology laboratory. Though the preferred method to achieve reproducible results and to make interlaboratory comparisons of GC data is by retention index (RI), the selectivity of the NPD has relegated its users to calculations of relative retention time. The present study utilizes a set of drugs as reference standards under temperature programmed conditions and presents a unique method of RI calculation. RI calculations are highly reproducible with this technique (day-to-day variations range from 0.3 to 3.4 RI units) and are comparable to packed column, FID generated reference data. A program, written in Basic, calculates RI values based on daily injections of the reference standards and searches a library of over 100 basic and acidic drugs.     

Quantitation of phencyclidine, its metabolites, and derivatives by gas chromatography with nitrogen-phosphorus detection: application for in vivo and in vitro biotransformation studies

A sensitive and specific assay for the quantitation of phencyclidine (PCP), its several metabolites, and derivatives in biological samples is described. The method is based on the extraction of PCP and related compounds with organic solvents followed by gas chromatographic (GC) separation with nitrogen-phosphorous (NP) detection of the extract derivatized with heptafluorobutyric anhydride. The detection limit was about 5 pmol per injection with a linear standard curve to 16 nmol in the initial sample. The recovery of different compounds ranged from 80 to 98%. Precision of the method was within 3 to 5%, while day-to-day variations did not exceed 5%. The present procedure permits the identification and quantitation of PCP and its major primary and secondary metabolites. In addition, several PCP analogs and derivatives that are not recognized as PCP metabolites can be quantitated using this procedure. The assay was applied for the quantitation of PCP and its metabolites in tissue homogenates and body fluids of PCP-dosed animals as well as in the urine of PCP-intoxicated humans. An in vitro system for PCP biotransformation studies by liver and placental microsomes was also developed.     

A rapid and sensitive method for the determination of paraquat in plasma and urine by thin-layer chromatography with flame ionization detection

A new method for the determination of paraquat in biological fluids has been developed. It involves thin-layer chromatography with flame ionization detection (TLC/FID) and simple solid-phase extraction with a disposable octadecylsilane column. This procedure allows direct loading of the samples on the disposable column. When Chromarod SII is used as the stationary phase and methanol-2N hydrochloric acid (2:3, v/v) as the mobile phase, recovery levels of paraquat in spiked materials are from 87.5 to 98.0%. This method can be used for samples of paraquat at levels as low as 50 ng.     

Simultaneous and rapid quantitation of benazepril and benazeprilat in human plasma by high performance liquid chromatography with ultraviolet detection

A sensitive and accurate high-performance liquid chromatography (HPLC) method with ultraviolet (UV) detector was developed and validated for simultaneous determination of benazepril (BZL) and its active metabolite, benazeprilat (BZT), in human plasma. The plasma sample, after spiked with riluzole as an internal standard (IS), was subjected to a solid-phase extraction (SPE) prior to a HPLC analysis. Chromatographic separations were achieved on a Hypersil BDS C(18) (300 mm x 4.6mm, 5 microm). The mobile phase consisted of phosphate buffer (pH 2.6; 10mM) and acetonitrile mixture in a gradient mode. Detection was carried out at a wavelength of 237 nm. The retention times of BZL, BZT and IS were at about 6.2, 15.4 and 16.2 min, respectively. The calibration curve was linear in the range of 20-2000 ng/mL for both BZL and BZT (r(2)>0.997). At three quality control concentrations of 100, 500, and 1500 ng/mL, the intra-day and inter-day relative standard deviation ranged from 2.8 to 8.6% for BZL and from 2.2 to 8.5% for BZT, while the mean absolute percentage error ranged from -7.5 to 6.7% for BZL and from -6.0 to 3.2% for BZT. The limit of detection (LOD) was 10 ng/mL and the limit of quantification (LOQ) was 20 ng/mL for both BZL and BZT in human plasma. The method was successfully applied to bioequivalence evaluation of benazepril hydrochloride formulations in healthy Chinese.     

Verapamil and norverapamil determination in human plasma by gas-liquid chromatography using nitrogen-phosphorus detection: application to single-dose pharmacokinetic studies

A sensitive (to 0.5 ng/ml) and specific method for the determination of verapamil and norverapamil which utilizes gas-liquid chromatography with nitrogen-phosphorus detection is described. A basic extraction with acid back-wash and final basic reextraction is used for the preparation of plasma samples. Standard curves using alpha-isopropyl-alpha-[(N-methyl-N-homoveratryl)-beta-aminoethyl]- 3,4- dimethoxyphenylacetonitrile hydrochloride (D-517) are linear for concentrations from 0.5 to 200 ng/ml for both verapamil and norverapamil. Within-day and between-day reproducibility is good with a coefficient of variation less than 10% for all concentrations. Recovery is complete for both verapamil and norverapamil. Application of the method is demonstrated by a pharmacokinetic study in a normal volunteer who received 10 mg verapamil hydrochloride by intravenous infusion.     

A rapid and sensitive LC-MS/MS assay to quantify yonkenafil in rat plasma with application to preclinical pharmacokinetics studies

A novel method for the quantitation of yonkenafil, a new synthetic phosphodiesterase V inhibitor, in rat plasma using high-performance liquid chromatography/tandem mass spectrometry (LC-MS/MS) has been developed. The analyte and internal standard (diazepam) were extracted from plasma (100 microl) by liquid-liquid extraction and separated on a C18 column using 10mM ammonium acetate buffer: methanol (15:85, v/v) as mobile phase in a run time of 3.0 min. The detector was a Q-trap mass spectrometer with an ESI interface operating in the multiple reaction monitoring (MRM) mode. The assay was linear over the concentration range 1.0-1000 ng/ml with a limit of detection of 0.20 ng/ml. Intra- and inter-day precision (as relative standard deviation) were both within 8.45% with good accuracy. The method was successfully applied to a preclinical pharmacokinetic study of yonkenafil in rat after sublingual, oral and intravenous administration. The results demonstrate that the sublingual route gives a higher bioavailablity than the oral route and may represent a useful alternative route of yonkenafil administration.     

Quantitative analysis of tiropramide in human blood by gas chromatography with nitrogen-phosphorus detector

The analytical method of antispasmodic agent tiropramide ((+/-)alpha-(benzoylamino)-4-[2-(diethylamino)ethoxy]-N,N-dipropylbenzenepropanamide hydrochloride) was developed by gas chromatography/nitrogen-phosphorus detector (GC/NPD) in human plasma. Two kinds of tiropramide tablets were orally administered to volunteers by Latin square crossover design, and blood was withdrawn as designed schedule. The plasma of 1 mL was loaded on Sep-pak C18 cartridge and eluted with methanol after washing with 30% methanol. The residue dissolved in 100 microL of methanol after evaporation was analyzed by GC/NPD. Precision (CV%) of intra-day was located within 2.6% and accuracy was less than 9.7%. Inter-day precision was below 8.7% and accuracy was relatively good as less than 14%. Plasma samples obtained from human volunteers were analyzed for the determination of tiropramide concentration by using this method. The method was sensitive, rapid and suitable enough to be applied for pharmacokinetic and bioequivalence studies of tiropramide in human volunteers.     

Simultaneous determination of nitrendipine and one of its metabolites in plasma samples by gas chromatography with electron-capture detection

A sensitive method for GC-ECD simultaneous determination of nitrendipine and its pyridine metabolite M1 in human plasma is described. Felodipine was used as the internal standard. The plasma samples were extracted with toluene. One microlitre of the extract was injected onto the capillary column (polymethylsiloxane) and measured with electron-capture detector. The developed method showed to be linear over the range 0.25-70 for nitrendipine and 0.3-61 ng/ml for its metabolite M1 with an inter-day and intra-day precision in terms of R.S.D. lower than 8% except the concentrations near lowest limit of quantification (LLOQ) (<11% R.S.D.). The LLOQ for nitrendipine was 0.25 and 0.3 ng/ml for its metabolite, respectively. The analytical recovery was 94% for nitrendipine and 89% for its pyridine metabolite M1. This GC-ECD method was developed for being used in clinical pharmacokinetic studies.     

高效液相色谱-质谱-质谱联用法测定人血浆中艾司西酞普兰浓度及其药代动力学研究

目的建立测定人血浆中艾司西酞普兰浓度的高效液相色谱-质谱-质谱联用法.方法血浆样品经甲醇沉淀后进行分析.色谱柱Lichrospher CN柱150 mm×4.6 m I.D.5μm,流动相甲醇水(含15 mmol·L-1乙酸铵)甲酸(72∶28O.1,v/v/v),流速1.0ml·min-1,电喷雾离子化三重四极杆串联质谱检测,以选择离子反应监测(SRM)扫描方式进行检测,采用选择离子反应监测(SRM)方式进行定量分析,用于监测的离子为m/z 325.0→234.0(西酞普兰)和m/z 409.1→238.1(氨氯地平,内标).结果线性范围为0.20～50.00ng·ml-1,最低定量浓度为0.20 ng·ml-1,应用此法测试了10名健康受试者口服草酸艾司西酞普兰片(10 mg)后不同时间的血药浓度,得到艾司西酞普兰药动学参数,Cmax为9.21±2.10 ng·ml-1,Tmax为3.75±1.04h,AUC0-t为514.6±152.3 ng·h·ml-1,AUC0-∞为540.5±162.3 ng·h·ml-1,t1/2为34.06±7.71 h及Ke为0.021±O.004h-1.结论该法专属、灵敏、简便、快速,适用于人血浆中艾司西酞普兰浓度的测定.     

A highly sensitive and specific radioimmunoassay for quantitation of plasma fluphenazine

Antisera of high sensitivity and selectivity were obtained from rabbits immunized with conjugates of hemisuccinylated fluphenazine and porcine thyroglobulin. The antiserum selected (titer 1:6000) for the development of the RIA was obtained after a priming dose and a single iv booster injection three months later. This antiserum had negligible crossreactivity with known available metabolites of fluphenazine (FPZ) and an affinity constant of 2 X 10(10) L/mol. Tritiated FPZ was further purified by HPLC and used as a ligand. The method detects as little as 20 pg/mL of plasma (4 pg/RIA tube) after 1 mL of plasma is extracted. The extraction was performed at a basic pH with heptane: isoamyl alcohol (99:1); the solvent was then back extracted using an acetic phosphate buffer. Recoveries were uniformly high (88.6 +/- 2.1%), and this aqueous buffer extract was used directly in the RIA procedure. The assay has intra- and interassay coefficients of variation of 5.8 and 8.2%, respectively, in a plasma concentration of 95 pg/mL. Results using this procedure have been cross validated against an HPLC procedure (r = 0.952, slope = 1.032, intercept = 0.009, n = 18). In a single-dose FPZ study (10 mg, po), plasma FPZ levels in 25 normal volunteers could be monitored greater than 48 h post dose. Single plasma level profiles, after an initial injection of 12.5 mg of FPZ decanoate, could be measured greater than 36 d, and, in some cases, up to 100 d post dose.     

Analysis of 4-methylpyrazole in plasma and urine by gas chromatography with nitrogen-selective detection

A simple, sensitive, and specific gas chromatographic method for the quantitation of 4-methylpyrazole in plasma and urine is described. Samples containing 4-methylpyrazole, with 3-methylpyrazole as the internal standard, are extracted into ether and the concentrated ethereal extracts are chromatographed on a Carbowax 20M column using nitrogen-selective detection. Standard curves are linear and reproducible over the range of 25-1000 ng/mL for plasma and 0.5-5 micrograms/mL for urine. Recovery of 4-methylpyrazole is complete from plasma and urine, and the overall between-day coefficient of variation is within 6.0%. No interference is observed from the extractive constituents of plasma and urine. The assay method is suitable for an examination of 4-methylpyrazole disposition in animals and humans.     

Development of a rapid and sensitive method for the quantitation of amphetamines in human plasma and oral fluid by LC-MS-MS

Target analysis of amphetamines in biological samples is of great importance for clinical and forensic toxicologists alike. At present, most laboratories analyze such samples by gas chromatography-mass spectrometry. However, this procedure is labor-intensive and time-consuming, particularly as a preliminary extraction and derivatization are usually unavoidable. Here we describe the development of an alternative method. Amphetamines were isolated from human plasma and oral fluid using a simple methanol precipitation step and subsequently analyzed using reversed-phase liquid chromatography-tandem mass spectrometry. Quantitation of the drugs was performed using multiple reaction monitoring. The developed method, which requires only 50 microL of biological sample, has a total analysis time of less than 20 min (including sample preparation) and enables the simultaneous quantitation of 3,4-methylenedioxymethamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxyethylamphetamine, amphetamine, methamphetamine, and ephedrine in a single chromatographic run. Limits of detection of 2 microg/L or better were obtained. The method has been validated and subsequently applied to the analysis of plasma and oral fluid samples collected from current drug users.     

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

A rapid and sensitive gas chromatographic method for the determination of the beta-adrenergic agent isoxsuprine in human plasma has been developed. The procedure involves the extraction of the drug with ether and an internal standard (propranolol) from plasma at alkaline pH, solvent evaporation, and the formation of a tri-trifluoroacetyl derivative by reaction with trifluoroacetic anhydride in ethyl acetate. Analyses were carried out by gas-liquid chromatography on a 3% OV-17 column using an electron capture detector. The minimum detectable amount of isoxsuprine was 0.5 ng/ml of plasma and the electron capture detector response was tested to be linear (r2 greater than 0.999) between 0.5 and 20 ng/ml. No interferences from endogenous substances were found. Precision of the method was found to be 9.9, and 6.1% coefficient of variation at 1 ng/ml and 10 ng/ml of plasma, respectively. Determination of isoxsuprine at the nanogram level in cord plasma samples from newborns at the time of the delivery was possible using the described procedure.     

Determination of felodipine in plasma by capillary gas chromatography with electron capture detection

Felodipine in plasma was extracted with toluene and determined by automated capillary gas chromatography with electron capture detection. Undesirable oxidation of the dihydropyridine derivative in the injector and in the column was avoided by the use of glass materials with the inner surfaces treated by high-temperature silylation. The day-to-day reproducibility of the method was represented by a relative standard deviation (RSD) of 5% for a felodipine concentration of 25 nmol/l. The minimum determinable concentration (giving better than 15% RSD) was 1–2 nmol/l (0.4–0.8 ng/ml).