Sample storage conditions and holding times for the determination of total iodine in natural water samples by ICP-MS

The determination of total soluble iodine concentration in fresh water by inductively coupled plasma mass spectrometry (ICP-MS) is simple and easy because no complicated pretreatment is needed; however, not all analysts have easy access to this instrumentation because it is expensive and has high running costs. In this study, sample storage conditions and holding times were examined for total soluble iodine measurement in standard and three river water samples by ICP-MS to provide more favorable circumstances for users. When standard solutions were stored at room temperature, the determined iodine at day 21 decreased by ca. 20% in the samples without adding an alkaline reagent, such as tetramethyl ammonium hydroxide (TMAH), probably due to I2 release from the solution. However, with the addition of a small amount of TMAH, iodine was retained in the solution and no decrease was observed. When the samples were stored at 5?, however, it was not necessary to add an alkaline reagent; for example, measured total iodine concentrations did not change for six months. Besides, measured total iodine concentrations in river water samples stored at 5? did not change for almost one year. The concentrations of total iodine in the three Japanese rivers (10 samples per each river) were all measured, and the concentration ranged from 0.33 to 3.87 micro g L-1, with an average of 1.16 micro g L-1