Analysis of Benzoic Acid in Quasi-Drug Drink Using Isotope Dilution Liquid Chromatography Mass Spectrometry

Abstract

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 13 C 6 -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− 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.

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“…The mass spectrometer was operated at negative ionization (ESI) mode with a spray voltage of −2500 V and a vaporizer temperature of 350 °C. Quantification was performed using multiple reaction monitoring (MRM); the MRM transition was m / z 121 → 77 (i.e., [M – H] → [M – CO 2 H] − ) . The gradient solvent program started from 90% acetonitrile in 5 mM ammonium acetate with a 1 min hold and then decreased to 50% acetonitrile over 4 min, followed by a return to 90% acetonitrile over 1 min and equilibrium for 1.9 min.…”

“…Considering, results for the short amplicons with C t ≥ 38.4 were recorded as nondetected (equivalent to 6 copies/μL for the sulI and 8 copies/μL for tetA). 43 The gradient solvent program started from 90% acetonitrile in 5 mM ammonium acetate with a 1 min hold and then decreased to 50% acetonitrile over 4 min, followed by a return to 90% acetonitrile over 1 min and equilibrium for 1.9 min. For quality assurance and quality control (QA/QC), samples diluted with methanol (10 μL of injection) were spiked with 10 μg of mass-labeled internal standard, benzoic acid-D5 (98%, Cambridge Isotope Laboratories, Inc., U.S.A.).…”