Avaliação de procedimentos de preparo de amostras de farinhas de oleaginosas para determinação multielementar por espectrometria de emissão óptica com plasma acoplado indutivamente

Abstract

Flours obtained from oilseeds (almond, peanut, coconut, and flaxseed) are widely consumed due to their functional properties and potential health benefits, including being a source of inorganic constituents such as Cu, Fe, Mn, Ni, Zn, Ca, K, P, and Mg, which play vital roles in the human body. Given the need to determine their nutritional values, the objective of this work was to develop sustainable analytical procedures for the preparation of oilseed flour samples for subsequent elemental determination by inductively coupled plasma optical emission spectrometry (ICP OES). 2³ factorial designs were applied to evaluate variables involved in acid decomposition procedures using a closed system digestion block (P1) and ultrasound assisted extraction (P2). The variables studied for P1 were temperature (160–180 °C), nitric acid concentration (3–7 mol L⁻¹), and time (60–120 min), and the response variable in the factorial design was the recovery percentage in relation to the reference method. The selected conditions were 3.0 mol L⁻¹ nitric acid, 160 °C, and 60 min of heating for approximately 0.25 g of sample, and the results obtained showed precision (RSD < 3%) and accuracy (recoveries between 88 and 110%) within the recommended range compared to the reference method. The limits of quantification (mg kg⁻¹) ranged from 2 to 34 for macroelements (Ca, Mg, P, and K) and from 0.09 to 4 for microelements (Cu, Fe, Mn, Ni, and Zn). The concentration ranges obtained (mg kg⁻¹) for the flours were: Cu (5.4–18.1), Fe (17.6–119.6), Mn (16.7–43.1), Ni (0.5–3.1), Zn (20.3–46.6), Ca (303–2641), K (6225–12033), P (4674–9238), and Mg (1742 2633). For procedure P2, the variables studied were temperature (30–60 °C), nitric acid concentration (1–2 mol L⁻¹), and sonication time (10–20 min), with the multiple response, obtained from the emission intensity of the elements of interest, used as the response variable in the factorial design. The recommended conditions for the determination of Cu, Fe, Mn, Zn, and K were 1.5 mol L⁻¹ nitric acid, 45 °C, and 10 min of sonication for 0.12 g of sample. The study also included the comparison of different nebulizers and the evaluation of the filtration step, demonstrating that these variables had a significant influence, contributing to greater precision (RSD < 3%). This method also showed precision (RSD < 3%) and accuracy (recoveries between 80 and 110%) within the established limits, with quantification limits ranging from 0.07 e 4 mg kg⁻¹. The concentrations obtained for the analyzed flours were, in mg kg⁻¹: Cu (5.0–17.5), Fe (12.7–90.6), Mn (14.1–43.1), Zn (21.5–45.5), and K (6073–13769). The Student’s t-test was applied to the results obtained by the two proposed methods in comparison with the reference method, and no significant differences were observed at the 95% confidence level, except for potassium in procedure P2, although the recovery percentages remained within the limits established by regulatory agencies. Multivariate analyses (PCA and HCA) were applied, revealing two main clusters that highlighted the similarity between almond and peanut flours, in contrast to the distinct profiles of flaxseed and coconut flours. Additionally, the AGREEprep metric was employed to compare the procedures regarding adherence to Green Analytical Chemistry principles, identifying ultrasound-assisted extraction as the more sustainable alternative.