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

Abstract

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 HNO₃ concentration were optimized. Quantitative recoveries were obtained using 15 min of extraction time and 0.6 mol L⁻¹ HNO₃. 0.48 mol L⁻¹ HCl was added after the extraction procedure in order to stabilize the analytes in the diluted HNO₃ 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.