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 (T₄) and 3,3′,5-triiodothyronine (T₃). A carbon disk electrode was used as working electrode in this system and exhibited a good response at 1.05 V (versus Hg/Hg₂Cl₂, 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 Na₂B₄O₇-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 T₃ (S/N = 3), respectively. The proposed method was applied to analyze T₄ and T₃ in pharmaceutical formulations, and the results were satisfactory.