Liquid-chromatographic determination of cinnamic and benzoic acids in benzoin preparations.

Abstract

Compound benzoin tincture (10 ml) was heated under reflux with ethanolic 0.5M-KOH for 1.5 h, the ethanol was evaporated and hot water was added. The soln. was cooled, water and 4% MgSO4 soln. were added, and the mixture was filtered. The filtrate was acidified with 0.5M-HCl and extracted with ether. The extracts were back-extracted with 5% NaHCO3 soln., the aq. layer was diluted with NaHCO3 soln., and a portion was diluted with mobile phase. A 10-µl aliquot was injected on to a column of LiChrosorb RP-18 (10 µm), with 0.01M-KH2PO4 (pH 5.8) - methanol (17:3) as the mobile phase and detection at 254 nm. The concn. of benzoic and cinnamic acids were calculated from calibration graphs (peak area vs. concn.). The average recoveries were 100.2 and 100.3%, respectively. The results were compared with those by the official BP titrimetric method.