Liquid chromatography (LC) is a key technique in the arsenal of an analytical chemist. The peak capacity of LC can be further increased by going from one-dimensional to comprehensive two-dimensional liquid chromatography (LC×LC). In conventional LC×LC, fractions of the effluent from the first- dimension (1D) are transferred to the second dimension (2D) by a modulation valve equipped with loops. However, the disadvantages of this approach are potential incompatibility issues, due to two mismatched solvent systems, and dilution, resulting in a decreased sensitivity. These problems can be overcome by using stationary-phase-assisted modulation (SPAM), which utilizes trapping columns to only retain the analytes on the column and discard the 1D eluent, so as to mitigate potential solvent incompatibility issues. With SPAM, the analytes are preconcentrated before entering the 2D column. It reduces the injection volume of the 2D separation and the associated band broadening. The major requirement for SPAM is that the analytes must be effectively retained on (and later released from) the trapping column. If the analytes are not retained, this will result in sample loss. A possible solution could be the addition of a dilution flow to increase the retention of the analytes on the trap column. Such a dilution flow is often chosen randomly, which does not eliminate the possibility of losing the early eluting compounds. In retention modelling, analyte-specific parameters are obtained by performing scanning experiments. These can be used to predict retention at different concentrations of organic modifier or for different gradients. In this presentation, the use of retention modelling will be demonstrated for developing and optimizing SPAM in LC×LC. First, the retention on trap columns in compared with that on analytical columns. Then, the best set of scanning-experiments on the analytical column is discussed for predictions on the trap columns. Finally, the retention is predicted as a function of the dilution flow. We will present a new tool that allows scientist to predict the applicability of SPAM in their setup without having to test trap columns.

Retention Modelling on Stationary-Phase-Assisted-Modulation Columns for Application in Two-Dimensional Liquid Chromatography

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ACS Fall 2022

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