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

We present the development and optimization of an analytical method based on Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS) for the analysis of multivitamin dietary supplements. Samples were ground and mixed with a cellulose powder containing internal standard elements; the resulting powder was pressed into pellets. Two calibration strategies were compared: (1) using increasing mass fractions of cellulose powder fortified with multiple elements of interest and (2) matrix matching using a multivitamin reference material in addition to the multi-element cellulose powder. Laser and ICP-MS parameters were closely monitored to achieve optimal conditions for monitoring multiple elements in cellulose and multivitamins while reducing the variability between replicate measurements. An energy output of 0.5 J/cm 2 , a repetition rate of 30 Hz, and a He carrier gas flow rate of 800 mL/min provided the best compromise between sensitivity and reproducibility. These parameters produced the most similar ablation behavior between cellulose and a matrix-matched calibration strategy. The dissimilarities in ablation yield due to differences in focus on the surface of the samples were successfully corrected after normalizing to an internal standard, resulting in relative differences of less than 10%. The results from the two different calibration approaches were compared to those obtained from solution-based ICP-MS and Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES) analyses. For most multivitamins, both calibration methods (i.e., cellulose and matrix-matched calibrations) performed adequately for As, B, Co, Cr, Cu, Mg, Ni, Na, Pb, and Zn. Matrix-matched calibration additionally resulted in better recoveries for S and Fe. Overall, matrix-matched calibration resulted in better recoveries for more multivitamins in comparison with cellulose calibration.