Purity Assessment of Honey Based on Compound Specific Stable Carbon Isotope Ratios Obtained by LC-IRMS

Abstract Background The use of stable carbon isotope ratios (δ13C) of sugar fractions of honey is a powerful tool to detect adulteration with sugar syrups. This is accomplished by calculating differences of the δ13C values between individual honey saccharides and comparing them to published purity criteria. A liquid chromatography–isotope ratio mass spectrometry (LC-IRMS) method for the determination of δ13C values of sugars in honey was previously validated by an interlaboratory comparison, but no further guidance was given how to include the obtained precision figures of the compound-specific δ13C values in the purity assessment of honey. Objective To use existing data to estimate the standard deviation of the repeatability (sr) and reproducibility (sR) of differences (Δ δ13C) between the δ13C values of individual honey saccharides. Methods Previously published δ13C values were used to calculate differences (Δ δ13C values) between δ13C fructose—δ13C glucose, δ13C glucose—δ13C disaccharides, etc. in a honey sample; sr and sR of Δ δ13C values were calculated according to ISO 5725–2:2019. Results The Δ δ13C sr and sR values were essentially of the same magnitude as the sr and sR values of δ13C values of the sugar fractions. The precision of the Δ δ13C values was used to estimate the critical difference for comparing a test result with a reference value according to ISO 5725–6:1994. This varied between 0.26 and 1.10‰. Conclusion The estimated critical differences can be used to determine whether a honey test result complies with published Δ δ13C purity criteria. Highlight The proposed procedure will increase confidence in decisions based on compound-specific δ13C values regarding the conformity of honey with published purity criteria.