Determination of mineral content of active dry yeast used in pharmaceutical formulations.

The efficiency of seven common methods of digestion of active dry yeast (ADY), which is used in anticariogenic dental formulations, was evaluated for the analytical determination of Fe, Zn, Ca, Mg, Na and K. Four wet-acid digestion and three dry ashing methods are compared in consideration of their estimated reproducibility and metal concentrations obtained. HNO(3), HNO(3)+HCl, HNO(3)+H(2)SO(4) and HNO(3)+HClO(4) were applied for wet digestion of the samples in medium temperatures, while dry ashing at higher temperature with Mg(NO(3))(2) or SrCl(2) as ashing aid agents, were the alternative methods. The final solutions were subsequently analyzed for Fe, Zn, Ca and Mg by flame atomic absorption spectroscopy (FAAS) and for Na and K by atomic emission spectroscopy (AES). Two multivariate statistical methodologies, Analysis of variance (ANOVA) and the Kruskal-Wallis test were applied for the interpretation of the results. Seven additional statistical tests (least-significant difference, Bonferoni, Duncan multiple range, Student-Newman-Keuls, Tuckey significant difference, Tuckey b and Scheffe) were used and proved useful to estimate which of the decomposition methods are outliers. The ideographic approach enabled the comparison of the methods in terms of complexity and difficulty of their steps. Zn and Mg could be reliably determined by any one of the tested methods, while for the other elements, the most powerful method was found and the obtained recoveries were found (>95%).