Sequential coprecipitation and matrix removal for determination of cadmium impurities from multivitamin supplements by inductively coupled plasma mass spectrometry and method validation by isotope dilution analysis of SRM 3280 multivitamin/multielement tablets

Abstract

In this paper, we examined three different sequential coprecipitation schemes based on Mg(OH) and CaF precipitation using triethylamine (TEA) and hydrofluoric acid (HF), respectively, for determination of cadmium (Cd) impurities from multivitamin/mineral (MVM) supplements by isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP-MS). The schemes involved three-step coprecipitation with either TEA alone or in combination with HF and are designated as Scheme 1 (TEA-TEA-TEA), Scheme 2 (TEA-HF-TEA) and Scheme 3 (HF-TEA-TEA) according to the addition sequence of each reagent. Experiments were carried out with MVM solutions spiked with 60 μg L Cd from a multielement standard solution. All schemes provided quantitative separation of Cd from MVM matrix. Scheme 1 was the least effective in removal of interfering concomitant elements, molybdenum (Mo) and tin (Sn). Scheme 2 performed better for Sn, but failed in eliminating Mo. Scheme 3 was the most effective in eliminating both Mo and Sn. Mo levels in test MVM solutions reduced from 4.3 μg mL to as low as 0.014 μg mL while that for Sn decreased from 0.5 μg mL to 0.018 μg mL allowing interference-free determination of Cd to be achieved. Salt-matrix due to Mg, Ca, P and K along with the essential elements (Mn, Fe, Cu and Zn) levels was also reduced significantly. Reagent blanks from HF and TEA were insignificant (0.008 μg L) allowing a limit of detection of 0.004 μg L or 0.26 ng g Cd to be achieved (3σ, n = 6). The performance of the coprecipitation method (Scheme 3) was validated by determination of Cd in multivitamin/multielement tablets certified reference material (SRM 3280) by ID-ICP-MS. Experimental results (ng g) and recoveries were 78.8 ± 4.7 (98.5%), 77.9 ± 5.2 (97.4%) and 76.5 ± 4.8 (95.6%) for Cd,Cd and Cd isotopes, respectively. Several commercial MVM supplements were analyzed using the method. Mean Cd concentration ranged from 21.4 ng g to 93.3 ng g. These values are much lower than those reported to date for various MVM supplements by ICP-MS determinations without chemical separation.

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

“…Ideally, MVM supplements should not contain any potentially toxic elements, such as arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) that cause harmful effects on human health under chronic exposure. Nevertheless, they do contain toxic elements at varying levels depending on the raw minerals, their origin and chemical processes used in manufacturing [13][14][15][16][17][18][19].…”

“…In recent years, there has been an increasing interest in monitoring As and Cd impurities in dietary MVM supplements owing to their adverse effects on human health [4,9,12,13,15,16,20]. Arsenic is known to cause hepatic, renal, reproductive, and nervous systems disorders [21,22].…”

“…A number of studies have revealed that commercial MVM supplements contain both As and Cd impurities at varying levels [4,9,12,13,15,16,20]. Dolan et al [15] reported as high as 4 µg g −1 As and 0.4 µg g −1 Cd in a number of dietary supplements.…”

“…Chronic exposure to high levels of As and Cd are concerning for humans, especially for children and pregnant women, and thus development of appropriate methods is imperative to accurately monitor their levels in MVM supplements. Currently, inductively coupled plasma mass spectrometry (ICP-MS) is the most popular technique for testing the toxic elements impurities in MVM supplements due mainly to its excellent sensitivity [15,16,20,[24][25][26]. Nonetheless, determination of trace As and Cd impurities is a difficult task due to the highly saline nature of MVM supplements.…”

“…Certified reference materials serve an indispensable role for quality assurance and development of suitable methods for elemental analysis of MVM supplements [16,27]. Recent reports, however, indicate that accurate measurements may not even be achieved with suitable reference materials owing to the fact that interferences of salt matrix could substantially confound the results from ICP-MS analysis.…”