Determination of levothyroxine and its degradation products in pharmaceutical tablets by HPLC-UV-ICP-MS

Journal of Analytical Atomic Spectrometry Pub Date: 2003-10-09 DOI: 10.1039/B307970H

Abstract

A new analytical methodology using high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) was applied to study the presence of possible degradation products in levothyroxine tablets. The analytical methodology takes advantage of the element-specific and highly-sensitive I detection provided by ICP-MS and is applied to the speciation of: 3,3′,5,5′-tetraiodothyronine (T4); 3,3′,5-triiodothyronine (T3); 3,5-diiodothyronine (T2); 3,3′,5,5′-tetraiodothyroacetic acid (TTAA4); 3,3′,5-triiodothyroacetic acid (TTAA3); and 3,5-diiodothyroacetic acid (TTAA2). Chromatographic conditions were optimized by using UV absorption at 225 nm and ICP-MS detection of 127I. Complete chromatographic resolution of the levothyroxine degradation products within 25 min was obtained using 22% (v/v) acetonitrile at pH 2.3, adjusted with 0.08% (v/v) trifluoroacetic acid. The introduction of the mobile phase containing acetonitrile was performed by post column on-line dilution (1∶3.3) of the chromatographic eluent with a 2% (v/v) nitric acid solution using a PTFE tee. The separations with either detector were good with little detector effect on the resolution. The peak broadening caused by on-line dilution was insignificant. The detection limits obtained with UV detection ranged from 28.9 to 34.5 μg l?1, whereas those obtained with the plasma detector were about 175–375 times better (lower). Finally, the analytical methodology was applied to the determination of possible iodine species originated by degradation of T4 in synthetic and commercial levothyroxine sodium tablets.

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