Improving Peak Capacity in Fast Online Comprehensive Two-Dimensional Liquid Chromatography with Post-First-Dimension Flow Splitting

Abstract

The use of flow splitters between the two dimensions in online comprehensive two-dimensional (2D) liquid chromatography (LC LC) has not received very much attention, in comparison with their use in 2D gas chromatography (GC GC), where they are quite common. In principle, splitting the flow after the first dimension column and performing online LC LC on this constant fraction of the first dimension effluent should allow the two dimensions to be optimized almost independently. When there is no flow splitting, any change in the first-dimension flow rate has an immediate impact on the second dimension. With a flow splitter, one could, for example, double the flow rate into the first dimension column and perform a 1:1 flow split without changing the sample loop size or the sampler’s collection time. Of course, the sensitivity would be diminished, but this can be partially compensated through the use of a larger injection; this will likely only amount to a small price to pay for this increased resolving power and system flexibility. Among other benefits, we found a 2-fold increase in the corrected 2D peak capacity and the number of observed peaks for a 15-min analysis time, using a post-first-dimension flow splitter. At a fixed analysis time, this improvement results primarily from an increase in the gradient time, resulting from the reduced system re-equilibration time, and, to a smaller extent, it is due to the increased peak capacity achieved by full optimization of the first dimension.