Analysis of Benzoic Acid in Drink Using ID-LC/MS

An analytical method was developed for the accurate determination of benzoic acid in commercial quasi-drug drinks using isotope dilution liquid chromatography mass spectrometry (ID-LC/MS). Sample drinks were spiked with C6-benzoic acid and these mixtures were cleaned by a nylon membrane filter. The sample mixtures were then analyzed using LC/Tandem MS in the negative ion mode without further clean-up or extraction steps. For the chromatographic separation, a C18 column with isocratic mobile phase of 50:50 (v/v) ammonium acetate buffer at pH 4.5 and methanol mixture was used. MS was operated with electrospray ionization in the negative mode. Benzoic acid and its isotope analogue were detected by selectively monitoring the collisionally-induced dissociation channels of [M-H]− → [M-CO2H] − at m/z 121 → 77 and m/z 127 → 83, respectively. Repeatability and reproducibility studies showed that the ID-LC/MS/MS method is a reliable and reproducible method which can provide less than 0.3% of relative standard deviation (RSTD) of method precision for analysis of benzoic acid.