Quantification of Arsenic Species in Wheat Flour Samples by Ion Chromatography Coupled to High Resolution Inductively Coupled Plasma-Mass Spectrometry (IC-HR-ICP-MS)

Abstract

A method was developed for arsenic speciation of South African wheat flour by microwave-assisted extraction with ion chromatography (IC) separation and detection with high resolution inductively coupled plasma–mass spectrometry (IC-HR-ICP-MS). Method optimization included development of the extraction and elution methods for baseline separation of the As-species in the samples. The As-species were successfully extracted using deionized water and baseline separation was attained using a gradient elution method with 0.5 mM HNO₃ (pH 3.4) and 50 mM HNO₃ (pH 1.4). Method validation parameters, including trueness (bias), precision, linearity, limit of detection (LOD), limit of quantification (LOQ) and selectivity were evaluated to assess the quality of the results. Three certified reference materials (CRMs), NIST SRM 1568b (rice flour), NMIJ CRM 7533-a (brown rice flour), and ERM BC211 (brown rice flour) were used to evaluate the trueness of the developed method. Low limits of detection and quantification were achieved (0.3 to 2.6 pg g⁻¹ and 1.1 to 8.6 pg g⁻¹, respectively) for the As-species. The dominant peaks in the wheat flour were arsenite (As(III)), dimethyl arsenic acid (DMA), and arsenate (As(V)). The concentrations of the inorganic (iAs), i.e., As(III) and As(V) in the wheat flour were very low from 6.8 to 17.8 ng g⁻¹, with a relative expanded uncertainty ( $U$) of <6.9% ( $k$=2), which is below the permissible level of iAs in food and food products proposed by the World Health Organization (WHO).