Development of Simple Method for Multi-elemental Determination of Inorganic Elements in Handmade Chocolate Employing Extraction Induced by Emulsion Breaking and MIP OES

Abstract

The objective of this work was the multi-element determination of Ca, Zn, Sr, Ba, Cu, Mn, Mg, and Cr in handmade chocolate samples after extraction induced by emulsion breakage (EIEB) using optical emission spectrometry with plasma induced by microwaves (MIP OES). After study of each parameter, the most efficient extraction conditions were obtained using 0.250 g of sample, 5.0 mL of extraction solution consisting of HNO₃ 1.5 mol L⁻¹ and Tween 80 1.5% m/v, submitted to an ultrasonic bath for 5 min, followed by breaking the emulsion by heating at 90 °C in a water bath for 4 min. The detection limits obtained, in mg kg⁻¹, were 0.35 (Cr), 0.013 (Zn), 0.064 (Sr), 0.083 (Ca), 0.46 (Fe), 0.010 (Ba), 0.099 (Cu), 0.016 (Mg), and 0.036 (Mn). Precision, based on the relative standard deviation (RSD%), was less than 9.8% (N = 7). The accuracy was confirmed by analyzing the SRM Baking Chocolate 2384 and comparing the proposed method with a calcination method. The method was applied to samples of chocolate bars made in the southern region of Bahia and containing cocoa contents at 50, 58, 60, 63, 70, 80, and 85%. The average results obtained were 328 to 1424 mg kg⁻¹ (Ca), 561 to 2152 mg kg⁻¹ (Mg), 7.8 to 251 mg kg⁻¹ (Cu), 8.5 to 304 mg kg⁻¹ (Mn), 6.22 to 98.32 mg kg⁻¹ (Fe), 8.38 to 80.2 mg kg⁻¹ (Zn), 3.4 to 175 mg kg⁻¹ (Ba), and 2.15 to 12.79 mg kg⁻¹ (Sr). It was observed that as the percentage increases cocoa, there is a tendency to increase the concentration of the studied elements. The developed method has satisfactory precision and accuracy, and is simple, fast and with low consumption of reagents, has good sensitivity, especially when compared to digestion methods.