Single Laboratory Validation of Determination of 13 Trace Elements in Rice by ICP-MS with an Overview of Challenges Encountered

Abstract

With the emerging concern on trace element content in rice on both toxicological and nutritional standpoints, validation of analytical method to determine both essential and toxic elements in rice is important in order to produce reliable results. Therefore, this study was aimed to validate analytical method to determine As, Cd, Pb, Hg, Cr, Ni, Se, Cu, Mn, Mo, Fe, Co and Zn in rice while giving an overview of the challenges encountered and application of the method to analysis trace elements in selected traditional rice varieties available in Sri Lankan market. Sample digestion was carried out by microwave digestion and analysed by ICP-MS. The analytical method was validated by measuring precision, accuracy, limits of detection (LODs), limits of quantification (LOQs), working and linear range, recovery percentage and measurement uncertainty. They showed that the method is fit for its purpose as those complies with the standard method performance requirements of AOAC. Percentage of relative standard deviations (RSD) of repeatability was not greater than 9.9% and RSDs (%) of reproducibility were not greater than 10.1% for all elements. Mean recoveries varied from 81% to 110%. Limits of detections of elements were in the range of 0.04 - 0.8 mg/kg and LOQs were in the range of 0.05 - 1.2 mg/kg. Expanded uncertainties of trace elements lay between 1.1% and 6.0%. Good agreement with the certified values of Standard Reference Material (SRM) 1568b—Rice Flour analysed by the proposed method with recovery percentages between 89.4% and 105.7% further confirms the accuracy and traceability of the method. The distribution pattern of essential elements in all rice varieties analysed was Mn > Zn > Fe > Cu > Mo > Se > Co. Even though arsenic was detected in all varieties, only the mean concentration of lead of Kaluneenati exceeds the maximum level (FAO/WHO CODEX Alimentarius).