Abstract

A method for the determination of the total As concentration in wheat flour samples from South African crops was developed based on a microwave-assisted digestion procedure. Different aspects of sample preparation, as well as optimization of the instrumental technique, such as strategies for signal enhancement, were investigated. The optimum digestion procedure was achieved using 6 mL nitric acid (HNO₃) with 40 µL hydrogen peroxide (H₂O₂) to facilitate the dissolution of the organic matter in the samples with gentle heating up to 95 °C over a period of 55 min. The analysis was performed using high resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS) for optimum interference control for As. The measurement trueness of the method was confirmed with an $E_n$-value = 0.01 calculated for the NIST SRM 1568b (Rice Flour) and an $E_n$-value = 0.9 calculated for the NCS ZC 80002b (Wheat) CRMs, respectively. The repeatability of the method was calculated to give a relative standard deviation (RSD) of <12%. The limit of detection (LOD) was 0.021 ng g⁻¹ for the samples in solution and the limit of quantification (LOQ) was 0.069 ng g⁻¹. This method was successfully applied to the analysis of 10 wheat flour samples with concentrations in the range of 5.5 to 12.3 ng As g⁻¹dry sample with a relative uncertainty of 11% ($k$=2). The concentrations of As in wheat flour samples obtained in this study were below the permissible levels of As allowed in food and food products.

摘要

基于微波辅助消解程序开发了一种测定南非作物小麦粉样品中总 As 浓度的方法。研究了样品制备的不同方面，以及仪器技术的优化，例如信号增强策略。使用 6 mL 硝酸 (HNO ₃ ) 和 40 µL 过氧化氢 (H ₂ O ₂) 以促进样品中有机物的溶解，在 55 分钟内温和加热至 95 °C。使用高分辨率电感耦合等离子体质谱 (HR-ICP-MS) 进行分析，以实现对 As 的最佳干扰控制。该方法的测量正确性得到了验证${乙}_n$-值 = 0.01 为 NIST SRM 1568b（米粉）和${乙}_n$- 值 = 0.9，分别针对 NCS ZC 80002b（小麦）CRM 计算得出。计算该方法的重复性以得到 <12% 的相对标准偏差 (RSD)。溶液中样品的检测限 (LOD) 为 0.021 ng g ^-1，定量限 (LOQ) 为 0.069 ng g ^-1。该方法成功应用于分析 10 个小麦粉样品，其浓度范围为 5.5 至 12.3 ng As g ^-1干样品，相对不确定度为 11% ($ķ$=2)。本研究中获得的小麦粉样品中的砷浓度低于食品和食品中允许的砷含量。