Facile and Accurate Analysis of Sodium Dehydroacetate in Cosmetic Powders After Extraction by Na2CO3-Methanol-H2O and Derivatization with 4-Nitrophenylhydrazine∙HCl

Sodium dehydroacetate (SDA) was extracted from cosmetic powders using a Na2CO3-methanol-H2O system. After the extract was neutralized, the resulting dehydroacetic acid (DAA) reacted with 4-nitrophenylhydrazine∙HCl (4-NPH∙HCl) to give the corresponding hydrazone, which was determined by an HPLC-VIS (400 nm) system. Using 4-NPH∙HCl in great excess was suitable for detecting the presence of DAA, which almost reacted with the hydrazine to yield the corresponding hydrazone. As a result, it was determined that contaminants in the cosmetic powder did not interfere with analysis of the hydrazone. Importantly, the molar absorptivity of the hydrazone (1.29 × 104 at 400 nm) is five times that of DAA (2.57 × 103 at 230 nm). Accordingly, detection of the hydrazone at 400 nm in a new analytical method might have fivefold higher sensitivity compared with that of DAA at 230 nm in the standard method.