Development of a Method Based on Slurry Sampling for Determining Ca, Fe, and Zn in Coffee Samples by Flame Atomic Absorption Spectrometry

Coffee is a source of mineral nutrients and, therefore, analytical procedures are needed for fast and reliable determination of metals in this matrix. This work proposes the development of a procedure for the determination of calcium, iron, and zinc in powdered coffee using slurry sampling and flame atomic absorption spectrometry (FAAS). The slurry liquid optimization was carried out using a constrained mixture design. Thus, for a mass of 0.1 g of the sample, this method allowed the determination of iron, calcium, and zinc with the limits of detection and quantification of 11 and 36, 18 and 60, and 10 and 32 mu g g(-1), respectively, and precision expressed as percent relative standard deviation (% RSD, 0.5 mg g(-1), N = 8), of 1.5, 1.2, and 2.1%. Accuracy was evaluated by (i) comparison of the generated values by the proposed method with that obtained by sample decomposition in acid media and (ii) analysis of a certified reference material (apple leaves NIST 1515). This method was applied to the analysis of industrialized and handcrafted coffees. The levels of iron, calcium, and zinc were found in coffees ranging from 41.5 to 186.0, 59.8 to 426.8, 38.6 to 58.7 mg g(-1), respectively. The application of the t test for the results, with a confidence level of 95%, showed no significant difference between the results generated by the proposed method and by digestion in acid media.