Determinação de micronutrientes minerais em amostras de suplemento alimentar por espectrometria de absorção atômica

Abstract

In this work, a sample preparation procedure with acid digestion in a microwave oven has been optimized for the determination of chromium by graphite furnace atomic absorption spectrometry (GF AAS) in three types of food supplement samples: whey protein, hypercaloric and protein bar. The instrumental parameters for the determination of Cr by GF AAS have been optimized by setting the temperature pyrolysis at 1100 °C for the analysis of samples of whey protein and hypercaloric and 1050 ºC for the analysis of samples of protein bar, the atomization temperature was set at 2300 ºC for all samples. The chromium concentration values were obtained by external calibration curve, validated through variance analysis, and ranged from 0.403 to 0.647 µg/g for protein bar samples, from 0.266 to 0.442 µg/g for hypercaloric samples and from 0.224 to 1.04 µg/g for whey protein samples. It was also observed the presence of chromium in samples without nutritional information related to chromium enrichment, in which some concentrations were above the one stated as the recommended daily dose for adults (35 µg). The X-ray diffraction (XRD) was used as a chemical tool to evaluate the chromium oxidation state in the food supplement samples. The results showed the presence of characteristic diffraction peaks of Cr+3 in the form of chromium picolinate to the three types of samples and the presence of diffraction peaks characteristic to Cr+6 in the form of chromium trioxide (VI), for samples of whey protein and hypercaloric. Sodium and potassium determinations were performed by flame atomic emission spectrometry (F AES). For the analytes quantification it was used the standard addition method. The sodium concentrations varied in the range of 1.4 to 5.4 mg/g, 0.3 to 3.5 mg/g and 0.4 to 8.8 mg/g, while the potassium concentrations varied in the range of 1.5 to 18.2 mg/g 0.5 to 6.5 mg/g and 3.3 to 33.7 mg/g for the samples of protein bar, hypercaloric and whey protein, respectively. Besides, these results obtained by F AES allowed the calculation of the Na/K ratios for the supplement samples. The values obtained (≤ 1) suggest they can be considered appropriate according to WHO recommendations. Finally, through an inter-laboratory tests the results obtained by ICP-MS, showing a good agreement at a 95% confidence level. It ensured the reliability of the presented data and conclusion.