The most common method for detecting the fraudulent dilution of vinegar with synthetic acetic acid is SNIF-NMR. Discrimination relies upon marginal differences in the stable isotope ratio of atoms at certain positions within the acetic acid molecular structure, dependent upon the synthetic pathway of the molecule. SNIF-NMR requires large sample sizes and long preparation times, and lacks transferability between laboratories.
Researchers have published (purchased required) an alternative method to discriminate acetic acid on a similar basis but using GC-pyrolysis-IRMS, using a sample preparation protocol that mitigates the problem of isotope-exchange with water. Although this method still uses specialist expensive laboratory equipment it is faster and more sensitive than SNIF-NMR. The authors consider the two methods to be complementary for building a body of analytical evidence.
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