DETERMINATION OF IODINE IN FOOD-RELATED CERTIFIED REFERENCE MATERIALSUSING WET ASHING AND DETECTION BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

Iodine was accurately determined in food-related certified reference m aterials (CRMs) by wet ashing in closed steel bombs using a mixture of nitric acid and perchloric acid followed by measurement of iodine by ICP-MS at m/z 127. The iodine concentrations determined were 0.15-4.59 mu g g(-1) (dry mass). Potentially volatile iodine species such as hy drogen iodide were converted during the ashing procedure to nonvolatil e species, Hereby memory problems in the ICP-MS due to volatile iodine were prevented, The concentric nebulizer which was used in combinatio n with a low dead-volume cyclonic spray chamber improved the iodine si gnal intensity and reduced the wash-out time between samples compared with the standard Ryton double-pass spray chamber equipped with a cros s flow nebulizer, Iodine contamination from the PTFE liners of the bom bs led to blank values at an average of 9 ng per ashing, The limit of detection which was based on three standard deviations of the blank wa s 30 ng g(-1) (dry mass), By adding 3% v/v methanol to the analyte sol utions and increasing the plasma power to 1200 W, the signal-to-noise ratio and hence the limit of detection was improved by 50% due to the signal enhancement effect by carbon of the incompletely ionized iodine .