Applications of laser ablation inductively coupled plasma mass spectrometry for monitoring impurities in solid foodstuff

The development of rapid and simple analytical methods that reliably monitor metal impurities in nutraceutical products is beneficial. An alternative solid sampling approach to quantify As, Cd, Hg, and Pb with LA-ICPMS is proposed in this work. This approach employs the incorporation of spiked organic binder standards with powdered raw materials in consistent ratios for the analysis of pressed pellets with LA-ICPMS. To date, LA-ICPMS calibration techniques have been limited by the inability to produce matrix matched standards and samples. This modified standard addition method provides a higher degree of matrix matching. It is hypothesized that LA-ICPMS will produce reliable analytical data for the analysis of elemental impurities in powders for the nutraceutical industry. Also, it is hypothesized that the incorporation of binders into analytical samples will be an effective way to accomplish standard addition. A Cetac LSX 500 266 nm Nd:YAG laser, and a Photon Machines Analyte G2 193 nm excimer laser were coupled to a Thermo XSeries2 ICP-MS to analyze berry, fiber and chondroitin samples in polyvinyl alcohol, microcrystalline and α-cellulose, and vanillic acid matrices under optimized laser conditions. USP 34 regulatory limits were used as guidelines to monitor As, Cd, Hg, and Pb. Quantification limits (LOQ) of 0.56, 0.13, 0.10, 0.10 μg/g were determined for As, Cd, Hg, and Pb respectively with the Nd:YAG laser. Similarly, the excimer laser gave LOQ of 0.063, 0.016, 0.057, 0.006 μg/g. All LOQ were capable of quantifying the impurities below regulatory limits. Accuracy validation with excimer laser gave recoveries ranging from 82 - 99% and 84 - 103% with scandium and yttrium normalizations in PVA respectively; the method precision met validation criteria of less than 20% RSD ranging from 5.4 to 19.8% for Pb and Hg respectively. Linearity validation studies gave R² values above 0.95 meeting acceptance criteria. The accuracy of Pb was maintained with both laser systems, and experimental values were within experimental uncertainty of the certified NIST 1547 and NIST 1486 reference values. The data supports that LA-ICPMS was a viable tool in generating reliable analytical data and that the incorporation of binders into samples effectively accomplished standard addition.

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