Application of extraction disks in dissolution tests of clenbuterol and levothyroxine tablets by capillary electrophoresis

Sample preparation procedures using octadecyl (C-18) extraction disks were developed to obtain accurate and reproducible results for determinations of clenbuterol (20 mu g per dose) and levothyroxine (100 mu g per dose) in dissolution media of solid oral dosage forms. Preconcentration of samples allowed final concentrations of 1.1 mu g/ml of clenbuterol and 4.0 mu g/ml of levothyroxine to be reached prior to CE analysis. The results obtained by CE were in good agreement with those of HPLC. The precision of the migration time, peak area, peak height and accuracy were determined in both intra-day (n = 6) and inter-day (n = 18) assays. Linearity was demonstrated over the ranges 0.5-80.0 mu g/ml of clenbuterol and 1.0-30.0 mu g/ml of levothyroxine. The mean recoveries were higher than 94.0%, ranging from 50 to 125% levels with respect to dose potencies. The proposed methodology may be generally applied to determine drugs at ng/ml concentrations.