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

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 (r(2)) 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 microg l-thyroxine/tablet) were in reasonable agreement with the value quoted.