Determination of Iodine in Food-related Certified Reference Materials Using Wet Ashing and Detection by Inductively Coupled Plasma Mass Spectrometry

Abstract

Iodine was accurately determined in food-related certified reference materials (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 mg g ⁻¹ (dry mass). Potentially volatile iodine species such as hydrogen iodide were converted during the ashing procedure to nonvolatile species. Hereby memory problems in the ICP–MS due to volatile iodine were prevented. The concentric nebulizer which was used in combination with a low dead-volume cyclonic spray chamber improved the iodine signal intensity and reduced the wash-out time between samples compared with the standard Ryton double-pass spray chamber equipped with a cross flow nebulizer. Iodine contamination from the PTFE liners of the bombs 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 was 30 ng g ⁻¹ (dry mass). By adding 3% v/v methanol to the analyte solutions and increasing the plasma power to 1200 W, the signal-tonoise ratio and hence the limit of detection was improved by 50% due to the signal enhancement effect by carbon of the incompletely ionized iodine.