Two dimensional LC-IRMS – The future of CSIA?

Compound-specific stable isotope analysis (CSIA) has many applications, including the investigation of micropollutant sources and transformation processes. The coupling of liquid chromatography (LC) with an isotope ratio mass spectrometer (IRMS) allows the measurement of analytes in complex water samples. The use of organic eluents, buffers or modifiers in LC-IRMS can lead to false determination of the carbon isotope signatures of the analytes and must be avoided. This limits the use of established chromatographic separations based on the use of organic eluents, which account for over 90% of current LC-methods. One way to overcome this limitation is to combine two-dimensional LC (2D-LC) with LC-IRMS. Adaptation of the 2D system allows LC-methods taken from the literature to be used with organic additives in the first dimension without the need for method development. The analyte of interest is then transferred to the second dimension via heart-cut modulation, where the organic solvents are separated from the analyte prior to oxidation. In this study, we aim to investigate the potential of 2D-LC-IRMS to make CSIA more accessible to a wider range of applications. The initial development and optimisation of a 2D-LC-IRMS system is presented. Further development will include testing different forms of heart-cut modulations, e.g. sample loop, trap column or multiple heart-cut modulators. The long term aim is to apply this instrumentation to mechanistic investigations and the measurement of complex real life samples.