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

A hyphenation of capillary electrophoresis (CE) to inductively coupled plasma mass spectrometry (ICP-MS) was employed for the speciation of iodine. The separation method used a buffer sandwich of phosphate (pH 2.3), NaOH, sodium dodecyl sulfate (SDS) and borate buffer (pH 8.3) for stacking, aiming at sufficient separation of iodide, iodate, thyroxine (T4) and triiodothyronine (T3). These four iodine species were separated within 15 min and subsequently 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 microg I/L (iodide), 0.3 microg I/L (iodate), 3.5 microg I/L (thyroxine) and 2.5 microg I/L (triiodothyronine). This method was applied on iodine speciation in human serum ("healthy" and after thyroid gland operation) and urine. The serum from the healthy person contained iodide (13 microg I/L), T4 (61 microg I/L) and T3 (7.5 microg I/L), whereas the serum from the thyroid-operated person lacked T3. As no "free" I-hormones are known in serum, the role of the thyroid hormone binding globulin (TBG) was investigated. We found that spiked T4 or T3 immediately bound to TBG. Investigations on human urine showed only a peak for iodide.