Method modified AOAC 2015.01 in the microwave conditions and the addition of HCl during sample digestion for simultaneous Pb, Cd, Hg, and As in infant formula using ICP-MS: a method validation

Abstract

The presence of heavy metals in infant formula has become a global concern. The most common method to determine heavy metals is AAS. However, as this technique is lacking in several aspects, including the instrument’s low sensitivity, a more sensitive instrument such as ICP-MS is necessary. The Inductively Coupled Plasma Mass Spectrometry (ICPMS) was used in accordance with the standard method AOAC 2015.01 with modifications on the microwave condition and the addition of hydrochloric acid (HCl) during the sample digestion process. The modified standard method requires a validation process. This research aimed to validate the method of analysis for the determination of Pb, Cd, Hg, As in infant formula using ICP-MS and its application in formula milk. This research consists of five stages: 1) instrumental performance; 2) homogeneity test; 3) method orientation; 4) method validation; and 5) the application of the validated method to other products. The findings in the research were: the method linearity was confirmed at working concentration 5-30 µg/kg for all the heavy metals with R2 value of nearly 1,000; the method limits of detection (LOD) were 0.74 µg/kg (Pb), 0.41 µg/kg (Cd), 0.08 µg/kg (Hg), 0.50 µg/kg (As), while the method’s limits of quantification (LOQ) were 2.48 µg/kg (Pb), 1.36 µg/kg (Cd), 0.27 µg/kg (Hg), 1.67 µg/kg (As); the method was found precise with Relative Standard Deviation (RSD) below 2/3 RSD Horwitz and all the recovery values were found to fall within the acceptable range (60–115%); the % RSD intra-lab reproducibility was below RSD Horwitz; and the method was robust, indicating that it was unaffected by small changes in its variables. The validated method can be applied routinely to determine heavy metals in infant formula and formula milk.