Iodine speciation in biological samples by capillary electrophoresis - inductively coupled plasma mass spectrometry

A hyphenation of capillary electrophoresis (CE) to inductively coupled plas ma mass spectrometry (ICP-MS) was employed for the speciation of iodine. Th e separation method used a buffer sandwich of phosphate (pH 2.3), NaOH, sod ium dodecyl sulfate (SDS) and berate buffer (pH 8.3) for stacking, aiming a t sufficient separation of iodide, iodate, thyroxine (T4) and triiodothyron ine (T3). These four iodine species were separated within 15 min and subseq uently detected during a pressure-driven detection step (baseline-separated ) at 19.5, 29.1, 36.6 and 42.2 s. The detection limits were determined at 0 .08 mu g I/L (iodide), 0.3 mu g I/L (iodate), 3.5 mu g I/L (thyroxine) and 2.5 mu g I/L (triiodothyronine). This method was applied on iodine speciati on in human serum ("healthy" and after thyroid gland operation) and urine. The serum from the healthy person contained iodide (13 mu g I/L), T4 (61 mu g lit) and T3 (7.5 mu g lit), whereas the serum from the thyroid-operated person lacked T3. As no "free" I-hormones are known in serum, the role of t he thyroid hormone binding globulin (TBG) was investigated. We found that s piked T4 or T3 immediately bound to TBG. Investigations on human urine show ed only a peak for iodide.