Determination of carbon isotope ratios for honey samples by means of a liquid chromatography/isotope ratio mass spectrometry system coupled with a post-column pump

RationaleLiquid chromatography/isotope ratio mass spectrometry (LC/IRMS) has been used to authenticate and trace products such as honey, wine, and lemon juice, and compounds such as caffeine and pesticides. However, LC/IRMS has several disadvantages, including the high cost of the CO2 membrane and blocking by solidified sodium persulfate. Here, we developed an improved system for determining carbon isotope ratios using LC/IRMS. MethodsThe main improvement was the use of a post-column pump. Using the improved system, we determined C-13 values for glucose with high accuracy and precision (0.1 and 0.1, respectively; n=3). The glucose, fructose, disaccharide, trisaccharide, and organic acid constituents of honey samples were analyzed using LC/IRMS. ResultsThe C-13 values for glucose, fructose, disaccharides, trisaccharides, and organic acids ranged from -27.0 to -24.2 parts per thousand, -26.8 to -24.0 parts per thousand, -28.8 to -24.0 parts per thousand, -27.8 to -22.8 parts per thousand, and-30.6 to -27.4 parts per thousand, respectively. The analysis time was a third to a half of that required for analysis by previously reported methods. ConclusionsThe column flow rate could be arbitrarily adjusted with the post-column pump. We applied the improved method to 26 commercial honey samples. Our results can be expected to be useful for other researchers who use LC/IRMS.