Laboratorio arbitral agroalimentario del Ministerio de Agricultura, Pesca y Alimentación, Crta. Coruña km 10,700, 28023 Madrid, Spain Journal of Agricultural and Food Chemistry (2006), V54 (26), pp 9719–9727, doi: 10.1021/jf062067x A new interface for the on-line coupling of a liquid chromatograph to a stable isotope ratio mass spectrometer Ana I. Cabañero , Jose L. Recio and Mercedes Rupérez A new procedure to determine individual sugar (sucrose, glucose, and fructose) 13C isotope ratios, using liquid chromatography-isotope ratio mass spectrometry (HPLC-IRMS), has been developed to improve isotopic methods devoted to the study of honey authenticity. For this purpose 79 commercial honey samples from various origins were analyzed. Values of d13Choney ranged from -14.2 to -27.2‰, and d13Cprotein ranged from -23.6 to -26.9‰. A very strong correlation is observed between the individual sugar 13C ratios, which are altered in the event of sugar addition, even at low levels. The use of ?d13C [fruct-glu], ?d13C [fruct-suc], and ?d13C [gluc-suc] systematic differences as an authenticity criterion permits the sugar addition [C3, beet sugar; or C4, cane sugar, cane syrup, isoglucose syrup, and high-fructose corn syrup (HFCS)] to be reliably detected (DL = 1-10%). The new procedure has advantages over existing methods in terms of analysis time and sensitivity. In addition, it is the first isotopic method developed that allows beet sugar addition detection.