LAUSR

A novel alternative to gradient elution in capillary supercritical fluid chromatography (SFC) based upon the systematic removal of a water stationary phase from the column, using a pure CO2 mobile phase, is introduced. By adjusting the flow of water used to humidify the system, the stationary phase can be removed at different rates and this results in proportionately faster analyte elution. As well, the phase can be readily restored within a few minutes. The method demonstrates good reproducibility with analyte retention times yielding an RSD of 1.2% in consecutive trials. Further, it provides results that compare well to a conventional pressure program in capillary SFC, but without the problematic convolution of system pressure and flow rate. The technique also demonstrated the ability to refocus analytes into sharper peaks, resulting in a 30-fold increase in their peak height. This effect can improve detection limits and also allow ionizable analytes like amines and dicarboxylic acids to be eluted with improved peak shape. Results indicate that systematic removal of a water stationary phase from the column is an interesting and potentially effective alternate means of controlling and improving analyte elution in capillary SFC.Graphical Abstract