Simultaneous separation of arsenic and cadmium from interfering salt matrix of multivitamin/mineral supplements by sequential coprecipitation and determination by inductively coupled plasma mass spectrometry

Abstract

Multivitamin/mineral (MVM) supplements possess highly saline matrix which, unless eliminated, precludes accurate determination of trace amounts of toxic metal impurities by inductively coupled plasma mass spectrometry (ICP-MS). Multi-step separations (up to four-steps) are described in literature; often for single element determinations due to difficulties in removing the matrix components. In this study, we developed a three-step sequential coprecipitation procedure for simultaneous separation of As and Cd impurities from MVM supplements for determination by ICP-MS. The procedure provided effective elimination of salt matrix, including Ca, Mg and KCl along with the interfering molybdenum (Mo) and tin (Sn) from MVM solutions. KCl, Mo and Sn were removed by two-step Mg(OH) 2 coprecipitation to about 34 µg mL −1 K (ca. 31 µg mL −1 Cl) and 0.4 µg mL −1 Mo. Levels of Sn and Na were not significant. A third coprecipitation of the resulting MVM solution with HF + NH 4 OH mixture precipitated virtually all Ca and Mg to as low as 1 and 10 µg mL −1 , respectively. The recoveries for As and Cd in the spiked MVM solutions were about 96% and 95%, respectively. The accuracy of the method was validated with analysis of multivitamin/multielement tablets certified reference material (SRM 3280). Experimental values were 112 ± 37 ng g −1 for 75 As, and 76 ± 5, 79 ± 5, and 78 ± 7 ng g −1 for 110 Cd, 111 Cd and 114 Cd isotopes, respectively, that were not significantly different from the certified values of As (132 ± 44 ng g −1 ) and Cd (80.2 ± 0.9 ng g −1 ) at 95% confidence level. Several commercially available MVM supplements were analyzed with the procedure. Mean As levels measured in the tablets varied between 24 and 128 ng g −1 and that for Cd were between 28 and 125 ng g −1 indicating total amount of As or Cd ingested per serving size were below the safe daily exposure limits. In addition, the results obtained for As and Cd with the procedure were lower in comparison to the values reported in literature indicating that ICP-MS analysis of complex MVM supplements could be prone to higher risks of inaccuracy without removal of interfering matrix.

Method Development for the Quantitative Analysis of Multivitamin Supplements by Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS)

“…For this reason, cadmium, mercury, potassium, and calcium were not reported. Cadmium isotopes suffer interferences from molybdenum oxide polyatomics, which formed in the ICP from high Mo concentrations in most of the multivitamins (Begu et al, 2019). Mercury was not determined above limits of detection in the solution analyses; therefore, it could not be compared to the LA-ICP-MS concentrations.…”

The Importance of Reference Materials and Method Validation for Advancing Research on the Health Effects of Dietary Supplements and Other Natural Products

“…The use of SRM 3280 for the determination of minerals and toxic elements (As, Cd) for both method development and validation has been reported by several researchers using ICP/MS ( 54 , 55 , 60 , 71 , 72 ) and AAS ( 63 , 69 ). Wolle et al used SRM 3280 for extraction method development in the determination of arsenic in dietary supplements ( 65 ).…”