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 + NH4OH 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 75As, and 76 ± 5, 79 ± 5, and 78 ± 7 ng g-1 for 110Cd, 111Cd and 114Cd 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.

中文翻译：

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通过连续共沉淀和电感耦合等离子体质谱法同时分离多种维生素/矿物质补充剂的干扰盐基质中的砷和镉

多种维生素/矿物质 (MVM) 补充剂具有高盐度基质，除非消除，否则无法通过电感耦合等离子体质谱法 (ICP-MS) 准确测定痕量的有毒金属杂质。文献中描述了多步分离（最多四步）；由于难以去除基质成分，通常用于单元素测定。在本研究中，我们开发了一种三步顺序共沉淀程序，用于从 MVM 补充剂中同时分离 As 和 Cd 杂质，以便通过 ICP-MS 进行测定。该程序有效地消除了 MVM 溶液中的盐基质，包括 Ca、Mg 和 KCl，以及干扰性的钼 (Mo) 和锡 (Sn)。KCl、Mo 和 Sn 通过两步 Mg(OH)2 共沉淀去除至约 34 µg mL-1 K（约 31 µg mL-1 Cl）和 0。4 µg mL-1 Mo。Sn 和 Na 的含量不显着。得到的 MVM 溶液与 HF + NH4OH 混合物的第三次共沉淀使几乎所有的 Ca 和 Mg 分别沉淀到 1 和 10 µg mL-1。加标 MVM 溶液中 As 和 Cd 的回收率分别约为 96% 和 95%。该方法的准确性通过对多种维生素/多元素片剂认证参考物质 (SRM 3280) 的分析进行验证。75As 的实验值分别为 112 ± 37 ng g-1，110Cd、111Cd 和 114Cd 同位素的实验值分别为 76 ± 5、79 ± 5 和 78 ± 7 ng g-1，与认证值无显着差异As (132 ± 44 ng g-1) 和 Cd (80.2 ± 0.9 ng g-1) 在 95% 的置信水平。使用该程序分析了几种市售的 MVM 补充剂。片剂中测量的平均砷水平在 24 到 128 ng g-1 之间变化，而镉的平均水平在 28 到 125 ng g-1 之间，表明每份摄入的砷或镉总量低于安全每日暴露限值。此外，与文献中报告的值相比，通过该程序获得的 As 和 Cd 的结果较低，表明复杂 MVM 补充剂的 ICP-MS 分析可能容易出现更高的不准确风险，而无需去除干扰基质。