A high-throughput method for multi-element determination in green coffee beans using diluted nitric acid and ultrasound energy

Different coffee varieties have been developed due to climatic particularities in Brazil; these varieties may have to overcome rigorous quality control that includes, among other, elemental determination, for which sample preparation is a critical step. Hence, this work describes the multivariate development of a straightforward method based on the use of diluted nitric acid and ultrasound-assisted extraction (UAE) followed by determination using inductively coupled plasma optical emission spectrometry and application for multi-element determination in newly developed varieties of coffee. The extraction time and HNO 3 concentration were optimized. Quantitative recoveries were obtained using 15 min of extraction time and 0.6 mol L −1 HNO 3 . 0.48 mol L −1 HCl was added after the extraction procedure in order to stabilize the analytes in the diluted HNO 3 solution. The accuracy of the method was evaluated comparing the proposed method with microwave-assisted digestion (MAD) and recovery tests. The UAE results were in agreement with those obtained by MAD according to a t -test at the 95% confidence level. A total of thirty-five coffee bean samples were analyzed using the proposed method. The results showed a variation in concentration from 0.2 to 4.5 μg g −1 for Ba, 1507 to 2576 μg g −1 for Ca, 5 to 30 μg g −1 for Cu, 17 to 44 μg g −1 for Fe, 30 771 to 55 741 μg g −1 for K, 2005 to 3327 μg g −1 for Mg, 12.1 to 148.8 μg g −1 for Mn, 1.0 to 7.6 μg g −1 for Sr, 1105 to 2766 μg g −1 for P, and 4 to 12 μg g −1 for Zn. It was also possible to obtain the correlation of elements and the variation in the elemental content, which was related to the cultivars, geographic location and year. This work describes the multivariate development of a straightforward method for multi-element determination based on the use of diluted nitric acid and UAE followed by determination using ICP-OES.