Multi-energy calibration and induced plasma optical emission spectrometry (MEC-MIP OES) as an alternative method for the multi-elemental determination of essential elements in cocoa

Abstract

The challenge of combining MEC-MIP OES arises from the limited number of emission lines available in this analytical technique. For the MEC-MIP OES optimization, the emission line wavelengths, sample dilution, proportion sample:standard for preparing MEC solutions, and nebulizer gas flow rate were studied. Then, the use of multi-energy calibration (MEC) and microwave-induced plasma optical emission spectrometry (MIP OES) was proposed as an alternative method for the determination of essential elements (Ca, K, Mg, Mn, and Na) in cocoa. In the optimized conditions, the method presented adequate analytical performance, with recoveries of 94–104 % and relative standard deviations lower than 5 %, showing adequate precision. The limits of detection (mg kg⁻¹) were 12 for Ca, 2 for K, 3 for Mg, 3 for Mn, and 6 for Na. The proposed method was applied to analyze cocoa samples cultivated in Brazil and Ecuador after acid decomposition. The results were in the range (mg kg⁻¹) of 409–1530 for Ca, 5520-13300 for K, 1460–3210 for Mg, 16–34 for Mn, and 28–61 for Na. Samples cultivated in Ecuador presented higher metal concentrations than the Brazilian samples. The proposed procedure was an easy and reliable approach for determining metals in cocoa samples, enabling multi-elemental determination with a lower cost and simplified calibration to be applied in routine applications.