US FDA: Elemental Analysis Manual: Section 4.11: Arsenic Speciation in Rice and Rice Products Using High Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometric Determination
Version 1.1 (November 2012)
Authors: Kevin M. Kubachka, Nohora V. Shockey, Traci A. Hanley, Sean D. Conklin
and Douglas T. Heitkemper
4.11.2 SUMMARY OF METHOD
HPLC-ICP-MS provides for sensitive, selective determination of arsenic species in rice.2-11 In this method, analytical samples of rice and rice-containing food products are composited and portions of the composite are mixed with a 0.28 M HNO3 solution and heated at 95°C for 90 minutes.5,6 The extracts are initially diluted with deionized water, centrifuged, filtered, and then diluted further while adjusting pH prior to analysis by HPLC-ICP-MS. The arsenic species are separated using an isocratic anion-exchange HPLC separation with a mobile phase of 10 mM ammonium phosphate dibasic at pH 8.25 (±0.05).12 The ICP-MS is used as an arsenic-specific detector monitoring m/z 75 for arsenic-containing chromatographic peaks and is operated in helium collision cell mode to eliminate interference from possible co-eluting chloride species. Arsenic species are identified by peak retention time match with arsenic species standards. Quantification of arsenic species is achieved using peak areas and an external calibration curve. Signal drift is corrected by adding a post-column internal standard.