Evaluation of non-aqueous capillary zone electrophoresis for the determination of histamine H2 receptor antagonists in pharmaceuticals.

A new non-aqueous capillary electrophoresis method is proposed for the separation and simultaneous determination of cimetidine, ranitidine, roxatidine, nizatidine and famotidine by using a 30-cm long × 75 µm i.d. fused silica capillary and UV detection at 214 nm. Using a temperature of 25°C, an applied voltage of 15 kV, and a background electrolyte consisting of methanol containing 10 mM ammonium acetate and 0.2% acetic acid allowed the analytes to be separated in less than 4 min. The limits of detection obtained ranged from 7 and 17 µg L(-1). The proposed method was successfully used to determine the analytes in pharmaceutical preparations and its results were checked against an HPLC method.

Capillary electrophoretic determination of methotrexate, leucovorin and folic acid in human urine.

A simple, rapid and sensitive procedure using capillary zone electrophoresis (CZE) to measure methotrexate, folinic acid and folic acid in human urine has been developed and validated. Optimum separation of methotrexate, folinic acid and folic acid was obtained on a 60 cm x 75 microm capillary using a 15 mM phosphate buffer solution (pH 12.0), temperature and voltage 20 degrees C and 25 kV, respectively and hydrodynamic injection. Under these conditions the analysis takes approximately 9.0 min. Good results were obtained for different aspects including stability of the solutions, linearity, accuracy and precision. Before CZE determination, the urine samples were purified and enriched by means of a solid phase extraction step with a preconditioned C(18) cartridge and eluting the compound with a mixture 1:1 of methanol:water. A linear response over the urine concentration range 1.0-6.0 mgL(-1) for MTX and 0.5-6.0 mgL(-1) for folinic acid and folic acid was observed. Detection limits for the three compound in urine were 0.35 mgL(-1). CZE was shown to be a good method with regard to simplicity, satisfactory precision, and sensitivity.

Development and validation method for determination of fluoxetine and its main metabolite norfluoxetine by nonaqueous capillary electrophoresis in human urine.

A simple, rapid and sensitive procedure using nonaqueous capillary electrophoresis (NACE) to measure fluoxetine and its main metabolite norfluoxetine has been developed and validated. Optimum separation of fluoxetine and norfluoxetine, by measuring at 230nm, was obtained on a 60cm x 75mum capillary using a nonaqueous solution system of 7:3 methanol-acetonitrile containing 15mM ammonium acetate, capillary temperature and voltage 25 degrees C and 25kV, respectively and hydrodynamic injection. Paroxetine was used as internal standard. Good results were obtained for different aspects including stability of the solutions, linearity, and precision. Detection limits of 10mugL(-1) were obtained for fluoxetine and its metabolite. This method has been used to determine fluoxetine and it main metabolite at clinically relevant levels in human urine. Before NACE determination, the samples were purified and enriched by means of extraction-preconcentration step with a preconditioned C(18) cartridge and eluting the compounds with methanol.

Determination of sildenafil citrate and its main metabolite by sample stacking with polarity switching using micellar electrokinetic chromatography.

Micellar electrokinetic capillary chromatography (MEKC) coupled with sample stacking and polarity switching was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320, UK) in human serum in the concentration range of clinical interest. Human serum samples spiked with SC and UK were eluted with methanol from a C18 cartridge, the extract was evaporated and regenerated in a solution that contained 1 mM phosphate buffer (pH 12.3) and 20% methanol. The MEKC separation was performed using an injection time of 275 s, a polarity switching time of 93 s, a phosphate buffer, (pH 12.3, 15 mM) containing 25 mM sodium dodecyl sulfate as separation electrolyte and a fused-silica capillary. The analysis takes about 6 min and gives satisfactory inter-day precision with respect to migration times and linear responses over the 80-900 ng/ml concentration range investigated for SC and UK. Intra-day RSDs (n=4 graphs) for the slopes of the calibration graphs were 4.86% for SC and 3.50% for UK. Inter-day RSDs for the slopes were 4.37% for SC and 5.39% for UK. Detection limits (S/N=3) were about 17 ng/ml for both compounds in human serum. A 1-ml volume of blood serum was necessary to do this determination.