Determinação de enxofre em shampoo por espectrofotometria UV-VIS: avaliação de métodos de preparo de amostras

Abstract

Dry ashing, dissolution in aqueous medium or wet digestion methods were evaluated for sample preparation of shampoo for the subsequent indirect determination of sulfur by UV-Vis spectrophotometry. Among the sample preparation methods evaluated, microwave-assisted wet digestion using 7 mol L-1 HNO3 was the most suitable method for this purpose. Accuracy of the proposed method was evaluated by recovery test using standard solution, and the recovery was about 96%. Moreover, for comparison of results, S (as SO4 2-) was also determined by ion chromatography, after microwave-assisted wet digestion using concentrated HNO3, and no significant difference was observed between the obtained results (according to the t-test for a 95% confidence level, p = 0.288). Relative standard deviations were always lower than 10% and the limit of detection was 0.007% w/v. Finally, the proposed method was applied for analysis of sixteen shampoos used to many types of hair, from different brands produced in Brazil, and the concentration of S ranged from 0.78 to 2.82% w/v.