HPCE determination of R(+) and S(-) mepivacaine in human serum using a derivatized cyclodextrin and ultraviolet detection.

A high performance capillary electrophoresis assay for the quantitative determination of R(+) and S(-) mepivacaine in human serum is reported using heptakis (2,6-di-O-methyl) beta-cyclodextrin as the chiral selector for the separation of the enantiomers. The background electrolyte was a 100 mM phosphate buffer (pH 2.5) containing 20 mM heptakis (2,6-di-O-methyl) beta-cyclodextrin and 30 nM hexadecyltrimethylammonium bromide (HTAB). A 72 cm uncoated fused silica capillary was used for the analysis. HTAB was used as the buffer additive to decrease the adsorption of endogenous substances onto the silica wall. To separate the analytes of interest from the endogenous serum substances, a liquid-liquid extraction procedure was used. The extraction recoveries were greater than 70% for both R(+) and S(-) mepivacaine. The detection limits were around 150 ng ml-1 using 1 ml of serum and the limits of quantitation were 200 ng ml-1. The calibration curves were linear over a range of 200-2000 ng ml-1 with R(-) prilocaine as internal standard (IS) and coefficients of determination were greater than 0.999 (n=3). Precision and accuracy of the method were 4.1-7.2 and 2.6-5.9%, respectively, for R(+) mepivacaine and 4.0-7.4 and 3.2-7.4% for respectively, for S(-) mepivacaine. The HPCE method was compared to an existing HPLC method in terms of sensitivity and selectivity for the routine analysis of the drugs.

Stereoselective determination of R-(-)- and S-(+)-prilocaine in human serum by capillary electrophoresis using a derivatized cyclodextrin and ultraviolet detection.

A capillary electrophoresis (CE) method for the quantification of R-(-)- and S-(+)-prilocaine in human serum was developed and validated. Stereoselective resolution was accomplished using 15 mM heptakis(2,6-di-methyl)-beta-cyclodextrin and 0.03 mM hexadecyltrimethylammonium bromide (HTAB) contained in 100 mM phosphate buffer, pH 2.5. Solid-phase extraction was used as a sample preparation technique to remove endogenous interferences. A 72-cm uncoated fused-silica capillary at a voltage of 25 kV and 30 degrees C was used for the analysis. The detection limits for R-(-)- and S-(+)-prilocaine were 38 ng/ml using 1 ml of human serum and the limits of quantitation were 45 ng/ml. The calibration curve was linear over the range of 45-750 ng/ml with procainamide as the internal standard. Precision and accuracy of the method were 2.86-8.50% and 3.29-7.40%, respectively, for R-(-)-prilocaine, and 3.94-9.17% and 2.0-6.73%, respectively, for S-(+)-prilocaine. The CE method was compared to an existing chiral HPLC method in terms of sensitivity and selectivity for the routine analysis of the drug.

Stereoselective determination of mepivacaine in human serum using a brush-type chiral stationary phase and solid-phase extraction.

A stereoselective high-performance liquid chromatography assay method was developed for the quantitation of R-(+)- and S-(-)-mepivacaine in human serum. The assay uses a Pirkle brush-type (S)-tert.-leucine, (R)-1-(alpha-naphthyl)ethylamine stationary phase (Sumichiral OA-4700, 250 x 4 mm I.D.) at ambient temperature with a mobile phase of hexane-ethylenedichloride-absolute methanol (85:10:5, v/v) for the separation of R-(+)- and S-(-)-mepivacaine. The eluents were monitored using UV detection at 220 nm. Isolation of the analytes from serum was performed using a 1-ml C18 solid-phase extraction cartridge with high recovery and selectivity. The detection limits were 100 ng/ml for each enantiomer and the limits of quantitation were 150 ng/ml for both enantiomers. Linear calibration curves in the 150-2400 ng/ml range showed good correlation coefficients (r > 0.9994, n = 3). Precision and accuracy of the method were within 2.1-5.3 and 2.0-3.6%, respectively, for R-(+)-mepivacaine and 2.7-5.7% and 1.7-4.2%, respectively, for S-(-)-mepivacaine.

Enantioselective determination of S-(+)- and R-(-)-ondansetron in human serum using derivatized cyclodextrin-modified capillary electrophoresis and solid-phase extraction.

A high-performance capillary electrophoresis (HPCE) assay method for the quantitation of S-(+)- and R-(-)-ondansetron in human serum was developed. Resolution was achieved using 15 mM heptakis-(2, 6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) in 100 mM phosphate buffer (pH 2.5). A 72-cm untreated fused-silica capillary, at a constant voltage of 20 kV, was used for the analysis. A 0.03-mM cationic detergent was used as a buffer additive to decrease the adsorption of endogenous substances onto the silica wall. The analytes of interest were isolated from endogenous substances using a solid-phase extraction procedure. The cyanopropyl cartridge gave good recoveries in excess of 85% for both S-(+)- and R-(-)-ondansetron, without any interferences. To decrease the limits of detection of the analytes, an on-capillary sample concentration technique was employed. The detection limit was 10 ng/ml using 2 ml of serum and the limit of quantitation was 15 ng/ml. The calibration curve was linear over a range of 15-250 ng/ml, with procainamide as the internal standard, and the coefficients of determination obtained were greater than 0.999 (n = 3). Precision and accuracy of the method were 2.76-5.80 and 2.10-5.00%, respectively, for S-(+)-ondansetron, and 3.10-6.57 and 2.50-4.35%, respectively, for R-(-)-ondansetron. The HPCE method is a useful alternative to existing chiral high-performance liquid chromatographic methods.

Stereoselective determination of R(-)- and S(+)-prilocaine in human serum using a brush-type chiral stationary phase, solid-phase extraction and UV detection.

A chiral HPLC method was developed for the quantitation of R(-)- and S(+)-prilocaine in human serum. The method involves sensitive and selective detection of R(-)- and S(+)-prilocaine using normal-phase chiral HPLC on a pirkle-type naphthyl ethylamine stationary phase (Sumichiral OA-4700, 250 mm x 4 mm i.d.) at ambient temperature with a flow rate of 0.8 ml min-1. A sample clean-up procedure was used for isolation of the analytes of interest from human serum using Bond-Elut C18 columns with high recovery and selectivity. The detection limits were 4 ng ml-1 for R-prilocaine and 5 ng ml-1 for S-prilocaine. The limits of quantitation were 10 ng ml-1 for both enantiomers. Linear calibration curves in the 10-1000 ng ml-1 range showed good coefficients of determination > 0.999 (n = 3). Precision and accuracy of the method were within 4-5.8% and 1.5-4.8% respectively for R(-)-prilocaine, and 2.8-5.7% and 3.2-5.2% respectively for S(+)-prilocaine.

Determination of fenbufen and its metabolites in serum by reversed-phase high-performance liquid chromatography using solid-phase extraction and on-line post-column ultraviolet irradiation and fluorescence detection.

An improved analytical method for the detection and quantification of fenbufen and its two major metabolites is described. The assay consists of reversed-phase high-performance liquid chromatography and post-column irradiation with ultraviolet light and fluorescence detection. A highly selective chromatography separation was established on a cyanopropyl column at ambient temperature with a flow-rate of 0.5 ml/min. The analytes of interest were isolated from serum using a Bond-Elut CIN column with high recovery and selectivity. The fluorescence response of all three analytes upon UV irradiation was investigated. The post-column UV irradiation was optimized and the effect of irradiation time on the fluorescence response was determined for all three analytes. The detection limits were 10 ng/ml for each analyte using 1 ml of serum. Linear calibration curves from 50 to 375 ng/ml for all three analytes show coefficients of determination of 0.99. Precision and accuracy of the method were within 3.9-6.5 and 5.1-7.4% for fenbufen, 3.5-6.4 and 4.9-6.3% for metabolite II (expressed as lactone III) and 5.4-7.4 and 2.6-7.4% for metabolite IV, respectively.

Determination of sulindac and its metabolites in human serum by reversed-phase high-performance liquid chromatography using on-line post-column ultraviolet irradiation and fluorescence detection.

On irradiation with ultraviolet light, the antiinflammatory agent sulindac and its two metabolites sulindac sulfone and sulindac sulfide form highly fluorescent derivatives. This reaction was exploited for the sensitive and selective detection of these compounds in serum using reversed-phase high-performance liquid chromatography on a Ultrasphere octylsilane column (150 x 4.6 mm I.D.) at ambient temperature with a flow-rate of 0.5 ml/min. The analytes of interest were isolated from serum using a Bond-Elut C2 column with satisfactory recovery and selectivity. The detection limits were 10 ng/ml for each of the three analytes using 1 ml of serum and the limit of quantitation was 50 ng/ml. Linear calibration curves from 50 to 1000 ng/ml for all three analytes show coefficients of determination of 0.9999. The post-column ultraviolet irradiation was optimized and the effect of irradiation time on the fluorescence response was determined for all three analytes. Precision and accuracy of the method were 0.4-5.6 and 1.6-4.5% for sulindac, 2.3-5.6 and 1.4-5.3% for sulindac sulfone and 2.5-4.3 and 0.8-2.8% for sulindac sulfide, respectively.