Analytical Sciences

Determination of Iodine and Bromine Compounds by Ion Chromatography/Dynamic Reaction Cell Inductively Coupled Plasma Mass Spectrometry

Kai-en WANG and Shiuh-Jen JIANG

Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic detector for the speciation of iodine and bromine. Gradient elution using NH₄NO₃ at pH 10 allowed the chromatographic separation of ionic iodine (I^- and IO₃^-) and bromine (Br^- and BrO₃^-) species in less than 8 min. Effluents from the ion-exchange column were delivered to the nebulization system of ICP-MS for the determination of I and Br. The potentially interfering ³⁸Ar⁴⁰ArH⁺ and ⁴⁰Ar⁴⁰ArH⁺ at the bromine masses m/z 79 and 81 were significantly reduced in intensity (by approximately two orders of magnitude) by using 0.6 mL min^-1 O₂ as a reactive cell gas in the dynamic reaction cell (DRC). Moreover, the signal-to-background ratio at iodine mass m/z 127 increased significantly when O₂ was used as the reaction gas. The detection limits were in the range of 0.001 - 0.002 and 0.03 - 0.04 ng mL^-1 for various I and Br compounds, respectively, based on the peak height. The relative standard deviation of the peak areas for five injections of a 2 ng mL^-1 I^-, IO₃^- and 20 ng mL^-1 Br^-, BrO₃^- mixture was in the range of 3 - 4%. The concentrations of I and Br compounds have been determined in selected water and urine samples. The spike recoveries were in the range of 94 - 102% for all of the determinations. This method has also been applied to determine various I and Br compounds in an NIST RM 8435 whole-milk powder reference material and a seaweed sample obtained locally. A microwave-assisted extraction method was used to extract these compounds, which were quantitatively leached with a 10% mass/volume (m/v) tetramethylammonium hydroxide (TMAH) solution in a focused microwave field within a period of 6 min. The major components of I and Br in milk powder and seaweed were I^- and Br^-.

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