Determination of glycyrrhetinic acid in human plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method has been developed for measuring 18 beta-glycyrrhetinic acid (GRA) in human plasma in the range of 0.1-3 micrograms/ml. The acetate ester of GRA is added to the plasma as an internal standard, plasma proteins are denatured with urea to release GRA, and the GRA and the internal standard are extracted in an ion-pairing solid-phase extraction process. An isocratic, reversed-phase HPLC separation is used, followed by ultraviolet absorbance detection at 248 nm. The results from the analysis of five GRA-fortified plasma pools show a mean relative standard deviation of 7% and are accurate to within 10%. With evaporative concentration of the extract, the limit of detection for GRA in plasma is approximately 10 ng/ml.     

Determination of mycophenolic acid in human plasma by high-performance liquid chromatography

The development, validation and evaluation of high-performance liquid chromatography (HPLC) method for quantifying mycophenolic acid in human plasma is described. The method involved protein precipitation using acetonitrile, after addition of terazosin as an internal standard. Separation was achieved with a reversed-phase C18 column (250 mm x 4.6 mm) employing UV detection at 215 nm. The mobile phase consisted of 0.02 M potassium dihydrogenphosphate solution adjusted to pH 6.9 with 2 M potassium hydroxide solution-acetonitrile (80:20 (v/v)) at a flow rate of 1.5 ml/min. The total run time was 21.0 min. The assay was linear from 0.2 to 25 microg/ml with goodness of fit (r2) greater than 0.99 observed with three precision and accuracy batches during validation. The observed mean recoveries were 89.3 and 98.0% for drug and internal standard, respectively. The applicability of this method to pharmacokinetic studies was established after successful application during a 34-subject bioavailability study. The method was found to be precise, accurate and specific during the study.     

Determination of metformin in plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of metformin, an oral antidiabetic agent, in plasma is described. Plasma samples containing the internal standard, phenformin, are eluted through Amprep extraction columns before injection into the chromatographic column, packed with microBondapak phenyl. The eluent is monitored at 236 nm. At a mobile phase flow-rate of 1.35 ml/min, the retention times of metformin and phenformin are 2.8 and 5.6 min, respectively. The intra-day coefficients of variation are 1.5 and 4.3% at metformin concentrations of 0.05 and 1 mg/l, respectively.     

Determination of p-chloronitrobenzene in plasma by reversed-phase high-performance liquid chromatography.

A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of p-chloronitrobenzene (p-CNB) in rat plasma. A plasma sample was deproteinized with methanol containing the internal standard (p-bromonitrobenzene). The resulting methanol eluate obtained after centrifugation was filtered and injected into a high-performance liquid chromatograph (50 microliters each). A column packed with 5 microns octadecylsilane (ODS) spherical particles was used with isocratic elution of methanol-water (45:55, v/v) at a flow-rate of 1.0 ml/min. The compounds were detected by ultraviolet absorbance at 280 nm. The retention times of p-CNB and the internal standard were 12.5 and 15.5 min, respectively, at a column oven temperature of 30 degrees C. The results were linear from 0.05 to 100 micrograms/ml (r = 0.999), and the detection limit was 0.01 microgram/ml. The relative error and the coefficient of variation on replicate assays were less than 7 and 10%, respectively, for all concentrations studied. The overall recoveries of p-CNB were between 97 and 105%. Plasma samples could be stored for up to one month at -20 degrees C.     

Determination of tetracyclines in plasma by high-performance liquid chromatography

A new method for the separation and quantitative determination of certain anti-biotics of the tetracycline series in blood plasma by high-performance liquid chromatography on a column filled with Partisil PXP 5 silica gel is described.I. M. Sechenov First Moscow Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 376–379, May–June, 1981.     

Determination by high-performance liquid chromatography of hydroxyurea in human plasma.

An assay using reversed-phase high-performance liquid chromatography with electrochemical detection was developed to measure hydroxyurea in plasma at concentrations suitable for pharmacokinetic studies. The sample preparation is simple, the analysis rapid and assays can be batched. The between-run precision is excellent (coefficient of variation = 2.8-4.5%) and the limit of detection is 0.02 mmol/l. Preliminary studies have shown that the method is suitable for pharmacokinetic studies.     

Determination of tetracyclines in plasma by high-performance liquid chromatography

A new method for the separation and quantitative determination of certain anti-biotics of the tetracycline series in blood plasma by high-performance liquid chromatography on a column filled with Partisil PXP 5 silica gel is described.     

Determination of four carboxylic acid metabolites of felodipine in plasma by high-performance liquid chromatography.

A reversed-phase high-performance liquid chromatography method with ultraviolet detection at 220 nm was developed to determine four carboxylic acid metabolites in plasma following therapeutic doses of the calcium antagonist felodipine. After the addition of an internal standard the analytes were isolated by liquid-liquid and solid-phase extraction. The metabolites were applied to a C2 cartridge in their free acid form, but they were transformed and retained as ion pairs with tetrabutylammonium during a wash with phosphate buffer (pH 7), prior to automated elution and injection by the Varian AASP system onto the analytical C18 column. Using a sample volume of 1 ml of plasma, the lower limit of determination for the metabolites was about 20 nmol/l. The influence of the pH of the mobile phase on the retention time of the metabolites and the structural requirements for the internal standard were studied. The method was applied to plasma samples from four dogs collected after an oral dose of felodipine. The plasma concentration-time profiles of the metabolites gave useful information about the mechanisms by which they were formed and eliminated.