ON-COLUMN UV ABSORPTION DETECTION IN LIQUID-CHROMATOGRAPHY WITH PACKED CAPILLARIES

Two modes of on-column UV absorption detection were investigated both theoretically and experimentally in liquid chromatography by using fused quartz capillaries packed with octadecyl-silica stationary phase, In the first detection mode, the column effluent is monitored by passing the light through the unpacked part of the capillary downstream of the bottom frit, In the second mode, light passes through a segment of the capillary that is packed with the stationary phase at a total porosity of epsilon(T). The efficiency of the chromatographic system was the same using either detection mode and the two modes of on-column detection were found to give equally reproducible results in both qualitative and quantitative analysis, The sensitivity of detection in the second mode was epsilon(T)(2)(1 + k') I mode for a peak having a retention factor of k' in isocratic elution under otherwise identical conditions. Thus, the second detection mode, with the light passing through the column packing, can have a higher sensitivity than the first with isocratic elution when k' is greater than (1 - epsilon(T)(2))/epsilon(T)(2). A further advantage of the second detection mode with the light beam traversing the packing is that this approach permits the monitoring of the chromatographic process at a multitude of axial positions in a packed fused silica capillary column. This application is illustrated by preliminary results in estimating the magnitude of extra-column band spreading and the intrinsic plate height of the packed capillary column in reversed phase chromatography.