Rapid Separation and Determination of Thyromimetic Iodoamino Acids by Gradient Elution Reverse Phase Liquid Chromatography with Electrochemical Detection

The usefulness and capabilities of gradient elution techniques with electrochemical detection are shown with a rapid separation of D,L-tyrosine (Tyr), 3-iodo-L-tyrosine (MIT), 3,5-diiodo-L-tyrosine (DIT), D,L-thyronine (T0), 3,5-diiodo-D,L-thyronine (T2), 3,3′,5-triiodo-L-thyronine (T3), and L-thyroxine (T4) by reverse phase liquid chromatography. A rapid (five minute) isocratic separation of T0, T2, T3, and T4 is also reported. Limits of detection are in the sub-nanogram range with a linear dynamic range to 500 ng for T2 and T3, and 1000 ng for T4. Analysis of levothyroxine sodium tablets and injectable intravenous samples is described.