AVALIAÇÃO DA COMBUSTÃO INICIADA POR MICRO-ONDAS PARA O PREPARO DE AMOSTRAS DE INSETOS COMESTÍVEIS E POSTERIOR DETERMINAÇÃO DE As, Cd e Pb

Abstract

The consumption of edible insects has been an alternative to the demand for food. However, potentially toxic metals (such as As, Cd, and Pb) can be present in these arthropods due to the substrates used in the production, which can affect the consumer's health. Therefore, analytical methodologies for the determination of As, Cd, and Pb in this type of sample need to be developed. Among the available analytical techniques, inductively coupled plasma mass spectrometry (ICP-MS) stands out for its multi-elemental character and for having low limits of quantification (LOQ). Nevertheless, operating in conventional mode, ICP-MS equipment requires that the sample to be analyzed is in liquid form, which demands a previous sample preparation step. Microwave-induced combustion (MIC) is a sample preparation method that stands out because it uses dilute solutions and results in digests with low values of carbon in solution compared to conventional acid digestion methods. Because of this, this work evaluates the use of MIC for the sample preparation of edible insect for further determination of As, Cd, and Pb by ICP-MS. For this, different insect samples (cricket, grasshopper, beetle and tenebrio molitor larvae) were dried, ground, and pressed into tablet form. The maximum sample mass (100 to 600 mg), the concentration of the HNO3 solution used as absorber solution (3 to 14.4 mol L-1) and the reflux time (5 to 15 min) were evaluated. Microwave-assisted acid digestion in a single reaction chamber (MAWD-SRC) was employed as a reference method. The accuracy was evaluated by comparing the results with the values obtained by the reference method and by analyzing the certified reference materials (CRMs, DORM-3 and DORM-5). The carbon content of the obtained solutions was determined by optical emission spectrometry with inductively coupled plasma (ICP-OES) and the concentration of As, Cd and Pb by ICP-MS. The MIC permitted combustion of up to 500 mg of sample and concordances above 90% for As, Cd and Pb were obtained using a 7 mol L-1 HNO3 absorber solution and 5 min reflux for the samples with ash contents up to 4.5%. Furthermore, for both CRMs there was no significant difference (t-student test) between the certified values for As, Cd and Pb and those obtained after MIC. The carbon content in the solutions obtained by MIC was less than 13.6 mg L-1, whereas the solutions obtained after the reference method had a content of 150 mg L-1 of C. For MIC, LOQs of 0.007, 0.003, and 0.040 µg g-1 were obtained for As, Cd, and Pb respectively, demonstrating that the proposed method is suitable for the preparation of edible insect samples and further determination of As, Cd, and Pb at low concentrations.