Multivariate optimization for the development of a sample preparation procedure and evaluation of calibration strategies for nutrient elements determination in handmade chocolate

Abstract

This study presents a procedure for microwave-assisted sample preparation of handmade chocolates with different levels of cocoa (30 to 85%) using 2.5 mol L−1 of HNO3 followed by determination of nutrient elements (Ca, Cu, Fe, K, Mg, Mn, P and Zn). The determinations were perfomed using inductively coupled plasma optical emission spectrometry (ICP OES). The optimization of the sample preparation procedure was performed using a Doehlert design, for evaluation of the following variables: volume de H2O2 and concentration of HNO3. The best condition for digestion of 200 mg of samples were obtained using only 5 mL of HNO3 at 2.5 mol L−1. In addition, three calibration strategies were evaluated: external calibration (EC), internal standardization (IS) and one-point standard addition (OP SA), and the EC showed the best results for the determination of the evaluated elements. The proposed procedure was validated and applied for the determination of Ca, Cu, Fe, Mg, Mn, P and Zn in 11 samples of handmade chocolates with different levels of cocoa produced in south region of Bahia State, Brazil. The concentration ranges for Ca, Cu, Fe, K, Mg, Mn, P, S and Zn found in the samples were compared with the values of recommended diary intake (RDI), inferring that handmade chocolates is a good nutrients source.