Determination of ¹³C/¹²C ratios of saccharides in honey by liquid chromatography – isotope ratio mass spectrometry

An interlaboratory comparison (ILC) was organised to provide an opportunity for interested laboratories to assess and compare their competence in determining the ¹³C/¹²C ratios of fructose, glucose, di- and trisaccharides in honey by using liquid chromatography – isotope ratio mass spectrometry. Fourteen laboratories participated in the ILC and tested six honey samples. For proficiency assessment, the mean values reported back by the participating laboratory were transformed into z-scores by using the consensus value (grand mean) and the reproducibility standard deviation.
For fructose 3 out of 84 z-scores (3.6 %) were |2| ≤ z ≤ |3|, for glucose 2 out of 84 (2.4 %) were |2| ≤ z ≤ |3| and 4 (4.8 %) were ≥ |3|, for disaccharides 2 out of 78 (2.6 %) were |2| ≤ z ≤ |3| and 2 (2.6 %) were ≥ |3|, for trisaccharides 2 out of 69 (2.9 %) were |2| ≤ z ≤ |3| and 3 (4.3 %) were ≥ |3|.
The majority of the participating laboratories demonstrated the proficient use of the applied LC-IRMS for mono-, di- and trisaccharides in honey, which will allow them to apply the technique for detecting adulterated honey samples within the scope of the method. Further guidance on the proper detection and evaluation of the oligosaccharide fraction will be needed to provide proof that the method is fit for compliance assessment of honey with purity criteria.
In general, the results of the ILC demonstrate that LC-IRMS is a suitable technique for determining carbon isotope ratios of fructose, glucose, di- and trisaccharides in honey with sufficient precision and it is fit for assessing whether sugar syrups have been added to honey, within the limits of the method.