There is a strong demand for the isotopic characterization of compounds in mixtures, which until now, could only be satisfied for on-line GC separations. The Finnigan LC IsoLink provides unique and easy access for LC and LC/MS users, to IRMS precision, via a simple on-line, direct coupling. High precision isotope ratio analysis is fundamental in the revealing of isotopic signatures, which in turn, offer insight into the history and origin of organic compounds. With the Finnigan LC IsoLink, the ratio of stable carbon isotopes, specifically ¹³C/¹²C, can be determined on-line with LC separation of the analyzed compounds. Applications include: authenticity of foods, flavors and drugs, determination of biodegradable cycles (metabolism studies) and doping control, to name but a few.