LCxSFC Valve\nTechnologies: Guidelines toward a Successful\nOnline Modulation

Online two-dimensional\nliquid chromatography can be used\nunder\nvarious separation modes but is sometimes limited in terms of orthogonality,\nespecially for the analysis of neutral compounds. The use of SFC in\nthe second dimension offers a wide choice of mobile and stationary\nphases, suggesting retention properties complementary to those of\nthe first dimension. Initial works on online LCxSFC coupling published\nin the literature highlighted the first difficulties of solvent compatibility\nor potential problems with bubbles created by CO<sub>2</sub> in loops.\nThe present work highlights the impact of the interface between the\nLC and SFC dimensions on the performance of the 2D separation. Six\ndifferent configurations have been evaluated, differing by the addition\nof a makeup flow in the first dimension, a division, or a separation\nof flow paths in the second dimension. Their performances with empty\nloops eliminated the need for complex trapping columns, regardless\nof the LC mobile phase nature. Injection in partial fill mode was\npossible without any problems of CO<sub>2</sub> bubble formation,\nsolvent miscibility, pressure, or modulation repeatability in each\nof the studied configurations. Selected configurations even allowed\nfor the use of a mobile phase split upstream of the valve, so that\nthe online LCxSFC configuration could be as flexible as LCxLC instrumentation\nin terms of the first dimension flow rate or second dimension injected\nvolume. The obtained results allowed for building guidelines presenting\nthe best interfaces to set up depending on the nature of the mobile\nphases in both dimensions. Two applications on monomers of lignin\nand industrial polymers confirmed preliminary results on configuration\ntesting and illustrated that online LCxSFC could now be easily implemented.\nPrecision tests on retention time were conclusive and are promising\nfor the future use of this technique in industrial routines.