Separation and simultaneous determination of the active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography

The separation and determination of seven active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography is described. On a 35 cm × 50 μm I.D. capillary, baseline separation is possible with a carrier solution containing 0.05 M sodium dodecyl sulphate (SDS) in 0.02 M borate buffer (pH 9.2) solution. The migration time of solutes increased markedly with increasing SDS concentration and slightly with increasing pH. With consecutive injections of samples, slight decreases in the migration times of the solutes occurred, but they were in parallel, owing to the temperature rise of the capillary with time. The column efficiency was influenced by the micellar concentration and applied voltage, and optimum values at which the highest theoretical plate number was achieved were established. The determination of the active ingredients was performed using hydrochlorothiazide and levamisole hydrochyloride (for ephedrine hydrochloride only) as internal standards, with good linearity with correlation coefficients from 0.9965 to 0.9999 and recoveries from 94.1 % to 101.1%. For quantitative information, measurements of peak height were better than peak area.