SOME SAMPLING EFFECTS IN LIQUID-CHROMATOGRAPHY

The relationship between column packing particle size and column efficienc y under mass overload conditions was examined with three silica-based packing materials of moderate surface area (sbet range 200–500 m2 g-1). An equivalent relation between reduced plate height, H/dp, and relative sample load, sample mass/ mass packing, was shown for all materials examined, both in the adsorption and reversed phase modes of chromatography over a narrow range of reduced velocity, udp/ Dm. The data were used in a simple calculation to establish the minimum dimensions of columns packed with dp=5/μm and 20/μm particles for a typical semi-preparative separation of a mixture of 20 mg each of two substances. A short study on the effect of variation of reduced velocity on reduced plate height at ‘analytical’ and semipreparative sample loadings showed that performance of LC columns in the preparative mode could be described reasonably well as a three dimensional surface in which the Y axis is reduced plate height, the X axis is reduced load, and the Z axis is reduced velocity. Some aspects of the performance of a ‘curtain-flow’ preparative precolurnn/column system are described along with an outline of the principles of design of this apparatus. Copyright © 1979, Taylor & Francis Group, LLC. All rights reserved.