Multi-element Determination in Craft Chocolate with Different Cocoa Contents Using Ultrasound-Assisted Extraction and Dilute Acid as Sample Preparation

This work evaluated the efficiency of an ultrasound-assisted extraction method using diluted acids to determine micronutrients and toxic elements in samples of craft chocolates with different cocoa content. Ca, Fe, K, Mg, Na, P, and Zn were determined through inductively coupled plasma optical emission spectroscopy (ICP-OES) and As, Cd, and Pb through inductively coupled plasma mass spectrometry (ICP-MS). For method optimization, the Mixture Plan type simplex-centroid was used, investigating HNO₃ (nitric acid), HCl (hydrochloric acid), and CH₂O₂ (formic acid) in the evaluation of the best extracting solution. The optimal condition indicated the usage of 10 mL of HNO₃ (2.0 mol L⁻¹) for extracting analytes from a mass of 200 mg at 50 ± 5 °C for 10 min of sonication. From the optimized method, limits of quantification vary from 0.030 to 15 mg kg⁻¹ for As and P, respectively, and precision is expressed as relative standard deviation (%RSD) below 10%. Aiming to evaluate the influence of cocoa content and the chocolate production region, the method analyzed 17 samples of craft chocolate from two different suppliers. The results were assessed by principal component analysis and demonstrated a possible influence of cocoa planting location in the presence of micronutrients and product concentrations. The concentration range of analytes found in the samples was compared with the daily recommended ingestion (DRI) values, concluding that this follows the maximum recommended values.