A Rapid Method for the Determination of Stable Hydrogen Isotope Ratios of Acetic Acid in Vinegar

RationaleVinegar is an everyday condiment made from fermented grains or fruits. It contains acetic acid which is the main organic material produced by fermentation. Vinegar suffers from the authenticity problem of exogenous adulteration due to the indistinguishability of low-cost chemical sources of synthetic acetic acid from acetic acid produced by fermentation. It is necessary to establish a simple and rapid measurement technique.MethodsDetermination was according to the total acid content of vinegar diluted with acetone to a certain concentration. Online separation and determination of acetic acid delta D in vinegar were carried out using gas chromatography-pyrolysis-isotope ratio mass spectrometry.ResultsAn HP-Plot/U column was selected for online separation of acetic acid and water with molecular sieve characteristics. At the same time, combined with the instrument blowback function to remove water. Dilute solvent acetone was treated with a molecular sieve to remove trace water. The reproducibility of this method is less than 3 parts per thousand. The long-term stability is within a reasonable error range. The accuracy correlation coefficient is greater than 0.99. The delta D values of acetic acid in vinegar (-264.5 +/- 20.3 parts per thousand) and from chemical sources (-30.5 +/- 90.8 parts per thousand) were obtained.ConclusionsA rapid method was developed for identification of different sources of acetic acid. These different sources of acetic acid exhibited significant hydrogen isotope distribution characteristics. Additionally, it was observed that the carboxyl hydrogen of acetic acid exhibited facile exchange with water. In future investigations, we aim to mitigate this interference.