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

• Published in: Química Nova 2017-05, Vol.40 (7), p.785-790
• Main Authors: Bielemann, Natalia J., Novo, Diogo L. R., Pereira, Rodrigo M., Mello, Julia E., Costa, Vanize C., Mesko, Marcia
• Format: Article
• Language: English
• Subjects: microwave-assisted wet digestion; sample preparation; shampoo; sulfur determination; UV-Vis spectrophotometry
• ISSN: 0100-4042; 1678-7064; 1678-7064
• DOI: 10.21577/0100-4042.20170052

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 SO42-) 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.