On a single method for determining As and Hg in dietary supplements by CVG-MIP OES: optimization of the multimode sample introduction system

Abstract

A single method was developed for the determination of As and Hg in dietary supplements by chemical vapor generation coupled with microwave-induced plasma optical emission spectrometry (CVG-MIP OES) using a commercial multimode sample introduction system (MSIS). The MSIS setup, general CVG conditions, and pre-reduction methods for the conversion of As(V) to As(III) were evaluated. It was possible to reach a magnification factor of 7 and 2 times for As and Hg, respectively, using the optimized MSIS setup compared to the standard setup. The proposed method provided a limit of quantification (LOQ) in the range from 5 to 15 and 29 to 93 ng g⁻¹ for As and Hg, respectively, which complies with the maximum concentration of 1.5 μg g⁻¹ for these elements in dietary supplements set by United States Pharmacopeia (USP) General Chapter 2232. This method was applied for the simultaneous determination of As and Hg in four classes of dietary supplements (vitamins and minerals, minerals, amino acids, and botanicals), which were previously digested by microwave-assisted wet digestion. The concentrations of both elements were found to be below the maximum limit established by USP General Chapter 2232 in all the samples. The accuracy of the proposed method was evaluated using certified reference materials (CRMs) and no statistical difference was observed between the reference and obtained values (t-test, confidence level of 95%). Also, no difference was observed in the results obtained using the proposed method with those using comparative methods (CVG-ICP-MS for Hg after wet digestion and ICP-MS for As after microwave-induced combustion (MIC)). After optimizing the MSIS setup and CVG conditions, the proposed method can be considered an alternative for the quality control of As and Hg in dietary supplements, given that it is suitable for the determination of these elements according to the limit established by USP.