We report on a comparative study of the basic separation kinetics of commercial packed bed columns and a micro-pillar array column (μPAC) working in the 1-10μL/min flow rate range, i.e., operating in the area of capillary flow LC. This is done using a basic test mixture of 8 alkylphenones under both isocratic and gradient separation conditions. Care was taken the μPAC and the packed bed columns have similar volumes (around 10μL) and hence also similar t0-times when compared at the same flow rate. In addition, the isocratic mobile phase composition and gradient programs were selected such to have similar elution windows (in absolute times) for all 4 column types. It was found that the μPAC produces significantly more theoretical plates (up to 3 times) in the 1-4μL/min range, while, the packed bed columns perform better at the higher flow rates because of the relatively large inter-pillar distance in the μPAC. Under gradient conditions, the μPAC produces a clearly higher peak capacity than any of the three packed bed columns over the entire range of investigated flow rates, albeit that this is also partly to be owed to the steeper gradient that needed to be used in the μPAC in order to maintain a similar elution window on all columns.
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