Sample preparation of lipstick for further Cd and Pb determination by ICP-MS: is the use of complexing acids really necessary?

Abstract

In this work, the use of complexing acids (HF and HCl) combined with HNO₃ was carefully evaluated for the digestion of several types of lipsticks and further Cd and Pb determination by inductively coupled plasma mass spectrometry (ICP-MS). Creamy, opaque and shimmering lipsticks were digested using HNO₃ (6 mL) or a mixture containing HNO₃ (6 mL) plus HCl (0.5 or 2 mL) or HNO₃ (6 mL) plus HF (2 mL). The results indicate that complexing acids are not required for the subsequent determination of Cd in all types of lipsticks evaluated. On the other hand, complexing acids were essential for ensuring quantitative results for Pb in shimmering lipstick. Thus, by using HNO₃ combined with only 0.5 mL of HCl, it was possible to obtain quantitative results for Pb and Cd in lipsticks. Under these conditions, recoveries for Cd and Pb were between 95 and 103%. No statistical difference was observed between the results obtained using the proposed method (HNO₃/HCl) and those obtained using HNO₃/HF, where a complete dissolution of the lipsticks' inorganic fraction occurred. Moreover, by using HCl, HF was avoided and solutions more compatible with ICP-MS analysis were obtained. The limits of detection for Cd and Pb were 3 and 77 ng g⁻¹, respectively. This method was applied for a variety of lipsticks, and the concentration of Cd and Pb ranged from <3 to 31 ng g⁻¹ and 271 to 2250 ng g⁻¹, respectively.