Determination of total and speciated arsenic in rice by ion chromatography and inductively coupled plasma mass spectrometry

Abstract

A method is presented for arsenic speciation analysis in rice using ion chromatography coupled to inductively coupled plasma mass spectrometry. Several procedures for the extraction of arsenic species from rice were investigated and compared. Treatment of the samples with 2 M trifluoroacetic acid for 6 h at 100 °C provided good extraction efficiency. Fortification recoveries were 83, 88, 100, and 93% for arsenite (100 ng As g−1), arsenate (100 ng As g−1), methylarsonic acid (MMA, 50 ng As g−1), and dimethylarsinic acid (DMA, 200 ng As g−1), respectively. The arsenate fortification recovery was calculated using the sum of the increase in arsenate and arsenite concentrations because arsenate was partially reduced to arsenite during the extraction process. Thus the sum of their concentrations is reported in this method as total inorganic arsenic. The sum of the arsenic species determined in NIST SRM 1568a rice flour (0.27 µg g−1 As), compared well with the certified total arsenic value (0.29 µg g−1 As). The speciation results obtained for 5 samples of long grain rice and one sample of wild rice are compared with total arsenic concentrations as determined by ICP-MS. The total arsenic concentrations ranged from 0.11 to 0.34 mg kg−1. The sum of the arsenic species extracted and determined by IC-ICP-MS ranged from 84 to 99% of the measured total arsenic concentrations. Inorganic arsenic accounted for 11–91% of the arsenic detected while DMA accounted for most of the remaining arsenic in the samples.