RESUMO
An acid digestion procedure of the forage palm (Opuntia ficus-indica Mill and Nopalea cochenilifera) employing a closed digestor block applied full 24 factorial design was optimized. The optimal conditions were HNO3 5.0 mol L-1, 2.0 mL of H2O2 30% m m-1, 120 min of digestion, and heating temperature of 180 °C. The certified reference materials of apple leaves (NIST 1515) and tomato leaves (Agro C1003a) were used to evaluate the accuracy of the analytical method. The concentrations of the macroelements were (in % m m-1) Ca (1.32-3.71), K (0.88-5.29), Mg (0.70-1.78), and P (0.03-0.32). For the microelements, the concentrations (in µg g-1) obtained were As (< 1.39), Cd (< 0.10), Cu (< 0.17-5.6), Fe (8.0-50.2), Na (< 1.85), Sr (41-348), and Zn (17.3-159). Essential elements such as Ca, Mg, and Zn made good contributions to daily intake, being an alternative to meet the nutritional needs of these macroelements and microelements in humans. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to evaluate the results, obtaining trends between the samples in relation to their mineral composition.
