Thermal modulation for multidimensional liquid chromatography separations using low-thermal-mass liquid chromatography (LC)

We report on a proof-of-principle experiment with a novel thermal modulation device with potential use in two-dimensional liquid chromatography (LC × LC) systems. It is based on the thermal desorption concept used in two-dimensional gas chromatography (GC × GC) systems. Preconcentration of neutral analytes eluting from the first dimension column is performed in a capillary "trap" column packed with highly retentive porous graphitic carbon particles, placed in an aluminum low-thermal-mass LC heating sleeve. Remobilization of the trapped analytes is achieved by rapidly heating the trap column, by applying temperature ramps up to +1200 °C/min. Compared to the nonmodulated signal, the presented thermal modulator yielded narrow peaks, and a concentration enhancement factor up to 18 was achieved. With a thermally modulated LC separation of an epoxy resin, it is shown that when the thermal modulation is applied periodically, the trapped and concentrated molecules can be released periodically and that the modulating interface can both serve as a preconcentration device and as an injector for the second dimension column of an LC × LC setup. Because of the thermal modulation, a high-molecular-weight epoxy resin could be adequately separated and the different fractions were identified with a GPC analysis, as well as an offline second dimension LC analysis.