A simple method for nicardipine hydrochloride quantification in plasma using solid-phase extraction and reversed-phase high-performance liquid chromatography

A simple and sensitive reversed-phase liquid chromatography method was developed and validated for the determination of nicardipine hydrochloride (NC) in rabbit plasma. Nicardipine hydrochloride and nimodipine, used as internal standard, were initially extracted from plasma by a rapid solid-phase extraction using C(18) cartridges. After extraction, nicardipine hydrochloride was separated by HPLC on a C(18) column and quantified by ultraviolet detection at 254 nm. A mixture of acetonitrile-0.02 M sodium phosphate buffer-methanol (45:40:15) with 0.2% of triethylamine of pH of 6.1 was used as mobile phase. The mean (+/-SD) extraction efficiency of NC was 77.56 +/- 5.4, 84.23 +/- 4.32 and 83.94 +/- 3.87% for drug concentrations of 5, 25 and 100 ng/mL, respectively. The method proved to be linear in the range of 5-100 ng/mL with a regression coefficient of 0.9993. The relative standard deviations of intra- and inter-day analysis for NC in plasma were 3.26-6.52% (n = 5) and 4.71-9.38% (n = 5), respectively. The differences of the mean value measured from the concentration prepared, expressed in percentages (bias percentage), were only - 5.2, 0.4 and 0.8% at NC 5, 25 and 50 ng/mL, which confirmed the accuracy of the method. The analytical technique was used to determine NC plasma concentration after drug oral administration to rabbits. The results inferred that NC is rapidly absorbed in rabbits and has a short half-life (t(1/2) = 1.34 h).     

A chromatographic method for baicalin quantification in rat thalamus

A rapid reversed-phase high-performance liquid chromatographic (rp-HPLC) assay for the determination of baicalin in rat thalamus was developed. This was carried out on a Hypersil -C(18) column using 4-nitro-benzoic acid as the internal standard with a mobile phase of methanol-water-H(3)PO(4) (45:55:0.2, v/v/v). Detection was by UV at 277 nm. The calibration curve for baicalin was linear (r=0.9992) over the concentration range of 0.05--4.0 microg/mL and the limit of detection was 10 ng/mL. The coefficients of variation of intra- and inter-day assays were 2.64, 5.19 and 3.19% and 3.46, 6.21 and 5.58% at concentrations of 0.5, 1.0 and 3.0 microg/mL, respectively. The recoveries of baicalin from rat thalamus were 85.4+/- 5.62, 90.7+/- 2.43 and 89.1+/- 4.75% at concentrations of 0.5, 1.0 and 3.0 microg/mL, respectively. The method was applied to determine the time course of baicalin in rat thalamus, following a single dosage of intravenous administration of Scutellariae radix extract at 90 mg/kg of baicalin to male Wistar rats.     

Improvement of cyclosporin A determination in whole blood by reversed-phase high-performance liquid chromatography

A chromatographic method was developed for the determination of cyclosporin A in human whole blood using reversed-phase HPLC at room temperature. Most previous reports carried out this liquid chromatographic separation at temperatures above 70 degrees C. The present procedure greatly improves the detection limit by controlling peak broadening effects, as well as the lifetime of the column at room temperature. Under optimal conditions and using ketoconazole as an internal standard, the calibration graph was linear in the range of 16-1000 microg/L with a relative standard deviation of 3.72% at 150 microg/L and 2.45% at 300 microg/L (n = 11) of cyclosporin A. The detection limit was of 5.0 microg/L cyclosporin A. By this procedure, cyclosporin A pharmacokinetic parameters in healthy Chinese subjects were studied. The developed method could be applied to the quantification of cyclosporin A in human blood samples and allows the study of its pharmacokinetics in routine laboratories.     

Determination of cymoxanil in drinking water and soil using high-performance liquid chromatography

We describe a method for determination of cymoxanil, 1-2-cyano-2-methoxy(iminoacetyl)-3-ethylurea, in drinking water and in soil, using reversed-phase HPLC with UV detection at 240 nm and a mobile phase of acetonitrile-water (30:70, v/v). Fortified water samples (1.0 L) were extracted with solid-phase extraction on Strata X. Soil samples (20 g) were extracted with acetone and the extracts were transferred onto Strata C18E. The recoveries of cymoxanil from water and soil samples were over 85% for each fortification level. The RDS were within the range 1.7-4.1% for water and 0.9-1.2% for soil samples. After optimization of the extraction and separation conditions, the method was validated.     

Determination of piceatannol in rat serum and liver microsomes: pharmacokinetics and phase I and II biotransformation

A method of analysis of piceatannol in biological fluids is necessary to study the kinetics of in vitro and in vivo metabolism and determine its concentration in foodstuffs. A novel and simple high-performance liquid chromatographic method was developed for simultaneous determination of piceatannol and products of its metabolism in rat serum and liver microsomes. Serum, or microsomes (0.1 mL), were precipitated with acetonitrile after addition of the internal standard, 4-methylumbelliferone. Separation was achieved on a phenomenex C(18) column (250 x 4.6 mm i.d., 5 microm) equipped with a phenomenex C(18) (4 x 3.0 mm i.d., 5 microm) guardcolumn with fluorescence excitation at 320 nm and emission at 420 nm. Separation was also possible with UV detection at 310 nm. The fluorescent calibration curves were linear ranging from 0.05 to 100 microg/mL. The mean extraction efficiency was >95%. Precision of the assay was <10% (coefficient of variation), and was within 10% at the limit of quantitation (0.05 ng/mL). Bias of the assay was lower than 7%. The limit of detection was 50 ng/mL for a 0.1 mL sample. The assay was applied successfully to the in vitro kinetic study of metabolism of piceatannol in rat liver microsomes and pharmacokinetics in rats. Three metabolites of piceatannol have been identified. .     

Development of solid-phase extraction method and its application for determination of hydrochlorothiazide in human plasma using HPLC

A high-performance liquid chromatographic method was developed, validated and applied for the determination of hydrochlorothiazide in human plasma. The effects of mobile phase composition, buffer concentration, mobile phase pH and concentration of organic modifiers on retention of hydrochlorothiazide and internal standard were investigated. The method involves solid-phase extraction on RP-select B cartridges followed by isocratic reversed-phase chromatography on a Hibar Lichrospher 100 RP-8 column with UV detection at 230 nm. The recovery, selectivity, linearity, precision and accuracy of the method were evaluated from spiked human plasma samples. Limit of quantification was 10 ng mL(-1). The method has been implemented to monitor hydrochlorothiazide levels in patient samples.     

Direct injection HPLC micro method for the determination of voriconazole in plasma using an internal surface reversed-phase column

A direct plasma injection liquid chromatographic method has been developed for the determination of a new triazole antifungal agent, voriconazole, using an internal surface reversed phase column. Therapeutic drug monitoring of voriconazole is relevant for patient management, especially in the case of drug-drug interaction. The method is easy to perform and requires 10 microL of a plasma sample. The chromatographic run time is less than 9 min using a mobile phase of 17:83 v/v acetonitrile-potassium dihydrogen phosphate buffer, 100 mM, pH 6.0 and UV detection at 255 nm. The fl ow rate was 1 microL/min. A linear response was observed over the concentration range 0.5-10 microg/mL (r2 = 0.977). A good accuracy (bias < or = 7.5%) was achieved for all quality controls, with intra-day and inter-day variation coefficients inferior to 6.7%. The lower limit of quantitation was 0.2 microg/mL, without interference of endogenous components. The stability of voriconazole in plasma stored at different temperatures was checked. Finally, the possibility of direct injection of plasma samples into the column permits a reduction in reagent consumption and in analytical steps, and hence in analytical error.     

Simultaneous determination of oxycodone and its major metabolite, noroxycodone, in human plasma by high-performance liquid chromatography

Oxycodone (14-hydroxy-7,8-dihydrocodeinone) is a potent opioid receptor agonist. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with UV detection was validated and applied for the analysis of oxycodone and its major metabolite, noroxycodone, in human plasma. The analytes were separated using a mobile phase, consisting of acetonitrile and phosphate buffer (8:92, v/v) at a flow rate of 1 mL/min, and UV detection at 205 nm. The retention times for oxycodone, noroxycodone and codein (internal standard) were 14.7, 13.8 and 10.2 min, respectively. The validated quantitation range of the method was 2-100 ng/mL for oxycodone and 10-100 ng/mL for noroxycodone. The developed procedure was applied to assess the pharmacokinetics of oxycodone and its metabolite following administration of a single 20 mg oral dose of oxycodone hydrochloride to one healthy male volunteer.     

Speciation of organotin and organoarsenic in water samples

Determination of tributyltin concentrations in water at low levels (0.1–1 ppt) is possible with the hydride generation/gas chromatographic separation/atomic absorption spectrophotometric method. This technique can easily be adapted for the determination of arsenic and methylated arsenic species. Arsenic (III) and arsenic (V) can be separated by selective coprecipitation with dibenzyldithiocarbamate.     

Synthesis,Structure and Acaricidal Activity of Tricyclohexyltin Benzoate

Tricyclohexyltin 4-amino-3-methyl-benzoate(1) and tricyclohexyltin 3,4-dimethoxybenzoate(2) were synthesized and their crystal structures were determined by X-ray diffraction. Compound 1 belongs to the monoclinic system, space group P21/c with a = 14.0554(15), b = 11.6947(13), c = 16.2720(17) , Z = 4, V = 2565.7(5) 3, Dc = 1.341 g·cm-3, μ(MoKα) = 1.016 mm-1, F(000) = 1080, R = 0.0833 and wR = 0.2964. Compound 2 is of monoclinic system, space group C2/c with a = 17.8712(6), b = 8.4433(3), c = 35.5783(13) , Z = 8, V = 5366.8(3) 3, Dc = 1.360 g·cm-3, μ(MoKα) = 0.980 mm-1, F(000) = 2288, R = 0.0549, wR = 0.1279. In compounds 1 and 2, the central Sn atom is coordinated in a tetradentate manner to assume a distorted tetrahedral configuration. Preliminary biological tests showed that these two compounds have strong acaricidal activity.     

HPLC determination of diltiazem in human plasma and its application to pharmacokinetics in humans

A simple and sensitive reversed-phase high performance liquid chromatographic method (HPLC) has been developed and validated for the routine analysis of diltiazem in human plasma and the study of the pharmacokinetics of the drug in the human body. Diltiazem and diazepa (internal standard) were extracted with a mixed organic solution of hexane, chloroform and isopropanol (60:40:5, v/v/v), and then HPLC separation of the drugs was performed on an Spherisorb C(18) column and detected by ultraviolet absorbance at 239 nm. The use of methanol-water solution (containing 2.8 mm triethylamine, 80:20, v/v) as the mobile phase at a fl ow-rate of 1.2 mL/min enables the baseline separation of the drugs free from interferences with isocratic elution. The method was linear in the clinical range 0-300 ng/mL and the lower limit of detection of diltiazem in plasma was 3 ng/mL. The range of percentage of relative standard deviation (%RSD) was from 3.5 to 6.8% for within-day analyses and from 6.2 to 8.4% for between-day analyses, respectively. The extraction recoveries of diltiazem from spiked human plasma (n = 5) at three concentrations were 91.4-104.0%. The method has been used to determine diltiazem in human plasma samples from eight volunteers who had taken diltiazem hydrochloride slow release tables and the data obtained was fitted with a program on computer to study the pharmacokinetics. The results showed that the peak level in plasma approximately averaged 118.5 +/- 14.3 ng/mL at 3.1 +/- 0.4 h, and the areas under the drug concentration curves (AUC) was 793.1 +/- 83.1 ng.h/mL.