Studies for analyzing restricted ingredients such as sodium benzoate

Sodium benzoate is a kind of preservatives in cosmetics and is nominated as the restricted ingredients in cosmetics in Japanese Pharmaceutical Affairs Act. So the analytical method for sodium benzoate was investigated by HPLC. After adding 5 ml of tetrahydrofuran to 0.05 g of the lotions or creams with 0.1 or 1.0% sodium benzoate and dissolving them, that mixture was made up to 50 ml with methanol. If necessary, the mixture was filtrated with a membrane filter (0.45 microm). The testing solution of 20 micro1 was analyzed by HPLC using the ODS column (CAPCELL PAK C18 column, 4.6 x 250 mm), the mixture of 50 mmol/l phosphate buffer (pH5.5) and acetonitrile (7:3) and the detection wavelength of 227 nm. The working curve from 1.0 to 12.0 microg/ml showed a linear line between the concentrations of sodium benzoate and the peak area. There was no interference of peak of sodium benzoate from the lotion and cream.