Simultaneous determination of thyroxine and triiodothyronine in pharmaceutical formulations using capillary electrophoresis with amperometric detection

A simple, reliable and repeatable method, based on CE with amperometric detection has been developed for the simultaneous separation and determination of thyroxine (T 4 ) and 3,3′,5‐triiodothyronine (T 3 ). A carbon disk electrode was used as working electrode in this system and exhibited a good response at 1.05 V ( versus Hg/Hg 2 Cl 2 , 3 mol/L KCl) for two analytes. The CE separations were investigated in detail. At 21 kV of applied voltage, the two compounds were separated within 11 min in 0.05 mol/L Na 2 B 4 O 7 ‐NaOH buffer (pH 11.3). And the detection limits were as low as 1.0×10 −7  mol/L for T 4 and 8.5×10 −8  mol/L for T 3 ( S/N =3), respectively. The proposed method was applied to analyze T 4 and T 3 in pharmaceutical formulations, and the results were satisfactory.