Study of physico-chemical properties of some packing materials .1. Measurements of the external porosity of packed columns by inverse size-exclusion chromatography

Previous work has shown that the beds of packing materials in conventional packed columns consolidate to a marked extent during an initial period. A detailed investigation of this phenomenon requires the development of a procedure for the accurate and precise determination of the external porosity of columns. This data can be obtained by inverse size-exclusion chromatography. We used a series of polystyrene standards with molecular masses ranging from 456 to 20 600 000 and injected them into four series of five chromatographic columns packed with Kromasil, Vydac, YMC, and Zorbax, respectively (all 10-mu m particles of C-18 bonded silica). The internal and external pore volumes (hence, porosities) of the columns can easily be determined with accuracy from the plots of the logarithm of the molecular mass of the probes versus their retention volume. This procedure offers a simple, fast, and convenient method for the determination of the external porosity of columns. This porosity correlates with retention data and equilibrium isotherms.