Development of a capillary electrophoresis method for the separation of flavonolignans in silymarin complex.

CE method for the baseline separation of structurally similar flavonolignans silybin A, silybin B, isosilybin A, isosilybin B, silychristin, silydianin, and their precursor taxifolin in silymarin complex has been developed and validated. The optimized background electrolyte was 100 mmol/L boric acid (pH 9.0) containing 5 mmol/L heptakis(2,3,6-tri-O-methyl)-ß-CD and 10% (v/v) of methanol. The separation was carried out in an 80.5/72 cm (50 µm id) fused silica capillary at +25 kV with UV detection at 200 nm. Genistein (10 µg/mL) was used as internal standard. The resolution between the diastereomers of silybin and isosilybin was 1.73 and 2.59, respectively. The method was validated for each analyte in a concentration range of 2.5-50 µg/mL. The calibration curves were rectilinear with correlation coefficients ≥0.9972. The method was applied to determine flavonolignans in two dietary supplements containing Silybum marianum extract. The accuracy was evaluated by comparing the results of the CE analyses of the dietary supplements with those of the reference United States Pharmacopeial HPLC method. The unpaired t-test did not show a statistically significant difference between the results of both the proposed CE and the reference method (p > 0.05, n = 3).

Fast assay of glucosamine in pharmaceuticals and nutraceuticals by capillary zone electrophoresis with contactless conductivity detection.

A novel capillary electrophoresis (CE) method with contactless conductivity detection suitable for the determination of glucosamine (GlAm) and K(+) in pharmaceuticals was devised. Under the optimum conditions (aqueous 30 mM acetate buffer of pH 5.2 as the background electrolyte; voltage 30 kV; 25 degrees C), GlAm (migrating as glucosaminium cation) was well separated from K(+) that could occur in the dosage forms as excipient. The CE analysis was performed in fused-silica capillaries (50 microm i.d., 75 cm total length, 27 cm to detector) and the separation took <3 min. The calibration graphs were linear for both GlAm (100-300 microg/mL; r(2)=0.997) and K(+) (15-75 microg/mL; r(2)=0.997) when using ethanolamine (100 microg/mL) as the internal standard. The LOD values (S/N=3) were 9.3 microg/mL for GlAm and 2.9 microg/mL for K(+). The method was applied to the assay of GlAm content in various dosage forms. Intermediate precision evaluated by determining the content of GlAm in a single formulation on 3 consecutive days was characterized by RSD 2.35% (n=15). Acceptable accuracy of the CE method was confirmed by the added/found GlAm recovery experiments (recoveries 94.6-103.3%) and by statistical comparison of the results attained by the proposed CE and a reference HPLC method.