HPLC Determination of Benzoic Acid and Sorbic Acid in Cosmetics with Sample Pretreatment by Solid Phase Extraction

The cosmetic sample was treated with methanol to dissolve benzoic acid and sorbic acid. After centrifugation, the supernatant was purified by passing through the RP C18 SPE microcolumn. The eluent from the column, after filtering and de-gassing, was used for HPLC analysis. Tweenty μL of the eluent were introduced into the instrument and separated on the Hypersil C18 RP chromatographic column (column temp. 30 ℃), using a mixed solution of methanol and 0.02 mol·L-1 NH4OAc solution (mixed in the ratio of 15+85) as mobile phase (with flow rate of 0.8 mL·min-1). UV detection at 221 nm was adopted in the determination. Values of detection limits (3S/N) for benzoic acid and sorbic acid was found to be 0.04 mg·L-1 and 0.08 mg·L-1, respectively. Precision was tested by using 5 mg·L-1 standard solutions of the 2 acids, giving values of RSD (n=7) 2.8% (for benzoic acid) and 2.5% (for sorbic acid). Recovery was tested by addition of standard solutions of the 2 acids, giving results of recovery in the range of 85.0%-106.7%.