Inductively coupled plasma optical emission spectrometric determination of fifteen elements in dietary supplements: Are the concentrations declared in the labels accurate?

Abstract

A study was carried out to establish a reliable procedure for determining 15 elements (As, Bi, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, V and Zn) in different brands of dietary supplements purchased in Argentina and USA. Supplements were digested with HNO3 and H2O2 using an optimized microwave procedure. Inductively coupled plasma optical emission spectrometry (ICP OES) was selected for total element determination. The overall approach was tested in tablets of: (i) Se supplement, (ii) two multimineral supplements, (iii) cholesterol control tablets, (iv) multivitamins for men, and (v) a multivitamin+multimineral supplement. Arsenic, Cd and Pb concentrations were in all the analyzed samples below the detection limits for these elements (As, 1.2 µg g-1; Cd, 0.09 µg g-1 and Pb, 1.5 µg g-1). Elemental concentrations of the other elements investigated showed a great variability depending on the trade mark analyzed. Measured metal concentration ranged from 0.78±0.19 µg g-1 (Ni) to 13.5±0.7 % (Ca). Most abundant elements, detected as percentage were Ca, Mg and Fe. In general terms, the study evidenced that metal content reported by the manufacturer in labels of dietary supplements agree with found values. On the other hand, significant differences in metal concentration were found among tablets of the same bottle.