Determination of iodide in urine using electrospray ionization tandem mass spectrometry

A rapid and sensitive electrospray ionization (ESI) tandem mass spectrometry (MS–MS) procedure was developed for the determination of iodide (I−). A gold (Au) and I− complex was formed immediately after the addition of the chelating agent NaAuCl4 to I− solution, and was extracted with methyl isobutyl ketone. One to five microliters of the extract were injected directly into an ESI–MS–MS instrument. I− quantification was performed by selecting reaction monitoring of the product ion I− at m/z 127 derived from the precursor ion 197AuI2− at m/z 451. I− concentration was measured in the quantification range from 10−7 to 10−5 M using 50 μL of solution within 10 min. Iodate was reduced to I− with ascorbic acid and determined. I− concentration in reference urine 2670a was measured after treatments.