METHOD DEVELOPMENT AND VALIDATION FOR THE DETERMINATION OF MINERAL ELEMENTS IN FOOD AND BOTANICAL MATERIALS BY CAPILLARY ELECTROPHORESIS

A capillary electrophoresis (CE) procedure was developed and validated for the determination of K+, Na+, Ca2+, Mg2+ and Mn2+ in solid natural products: Closed-vessel microwave acid digestion [HNO3-H2O2 (2:0.5)] was used for the sample preparation. Digests of these samples were diluted with deionized water and the resulting solutions injected for CE. The excess of nitric acid in the samples was found to influence the analytical performance, so its effect was investigated in detail. Direct calibration with aqueous standard solutions was applicable for the analysis of all sample types. To evaluate the bias of the proposed procedure, reference materials were analysed. The results agreed well with the certified or recommended values. The precision of the procedure was evaluated with a two-level nested analysis of variance. This allows one to estimate separately the variance due to three factors (the CE measurement, the sample preparation and time) that are expected to contribute to the variability of the measurement results. For all the elements determined, the CE system repeatability (R.S.D.) was smaller than 4%, method repeatability smaller than 6% and the within-laboratory reproducibility smaller than 9%. The limit of detection (LOD) and limit of quantification (LOQ) in solution are below 600 mu g/l, except for K+, for which the LOQ is about 2 mg/l.