Determination of thyroxine in pharmaceuticals using flow injection with luminol chemiluminescence inhibition detection

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Abstract
A simple flow injection method is reported for the determination of thyroxine, based on its inhibition effect on luminol–iron(II) chemiluminescence in alkaline medium in the presence of molecular oxygen. The detection limits (2s) for d‐ and l‐thyroxine are 0.08 and 0.1 mg/L, respectively, with a sample throughput of 100/h. The calibration data for d‐ and l‐thyroxine over the range 0.2−1.0 mg/L gives correlation coefficients (r2) of 0.9915 and 0.984 with relative standard deviations (RSD; n = 4) in the range 1.2−2.8%. The effects of some organic compounds was studied on luminol‐iron(II) CL system for thyroxine determination. The method was applied to pharmaceutical thyroxine tablets and the results obtained (in the range 50.5 ± 2.0−51.6 ± 1.2 µg l‐thyroxine/tablet) were in reasonable agreement with the value quoted. Copyright © 2006 John Wiley & Sons, Ltd.