Impurity profiling of dexamphetamine sulfate by cyclodextrin-modified microemulsion electrokinetic chromatography.

A CD-modified microemulsion electrokinetic chromatography method has been developed and validated for dexamphetamine sulfate which allows the simultaneous determination of charged and uncharged impurities of the drug including the levorotary (R)-enantiomer. The optimized background electrolyte consisted of 1.5% w/w SDS, 0.5% w/w ethyl acetate, 3.5% w/w 1-butanol, 2.5% w/w 2-propanol and 92% w/w 50 mM sodium phosphate buffer, pH 3.0, containing 5.5% w/w sulfated β-CD. Separations were performed in a 50.2/40 cm, 50 μm id fused silica capillary at a temperature of 20°C and an applied voltage of -14 kV. Carbamazepine was used as internal standard. The assay was validated in the range of 0.1-1.0% for the related substances and 0.1-5.0% for levoamphetamine based on a concentration of 3 mg/mL of dexamphetamine sulfate. The LOD of all analytes ranged between 0.05 and 0.2%. In commercial samples of dexamphetamine sulfate, levoamphetamine was found at concentrations between 3.2 and 3.8%, whereas none of the other impurities could be detected.