Influence of Digestion Procedure and Residual Carbon on Manganese, Copper, and Zinc Determination in Herbal Matrices by Atomic Absorption Spectrometry

Abstract

Mineralization to the complete oxidation of sample carbon component does not always assure the best analyte recovery. Particular attention should be paid to the presence of silicon in the investigated plant sample and especially in the certified reference material for which Si content is scarcely given by the providers. During mineralization without addition of the hydrofluoric acid, the residual carbon may block silica surfaces and increase availability of an analyte for its spectral determination in the solution. This issue is of particular relevance because standard protocols for digestion of plant matrices often do not support hydrofluoric acid addition. Several procedures recommended for decomposition of herbal plants were applied for the respective certified reference material and examined in detail. Manganese, copper, and zinc contents were analyzed in all samples by the flame atomic absorption spectrometry. Additionally, the residual carbon was determined in all mineralizates. Silicon content was analyzed by the X-ray fluorescence method. The best recoveries were observed for samples characterized by relatively high residual carbon.

Figure 1

Recoveries versus NPOC as determined for all protocols which were applied for microwave digestion in a closed system: (a) Mn, (b) Zn, and (c) Cu.

Figure 2

Results of the one-way ANOVA calculations for manganese (a); zinc (b); copper (c) content as compared for all pairs of investigated methodologies. Grey squares represent combinations for which average concentrations are equal at the 0.95 probability level. Numerical values are given in the supplementary materials.