The ultimate band compression factor in gradient elution chromatography

The equations predicting the ultimate time band compression factor, G=(tR−tF)/tpG=(tR−tF)/tp in linear gradient elution chromatography, for an infinitely narrow injection (injection time tp→0tp→0) were derived for an ideal-model column (dispersionless chromatography, H=0H=0) assuming the Linear Solvent Strength Model for the retention behavior of the analyte. Numerical solutions can readily be obtained when the LSSM model does not apply. The results can be generalized to any retained organic modifier (kA′) in the mobile phase. The stronger the retention of the organic modifier, the more effective the band compression. Dispersion in real chromatographic column (H≠0H≠0) affects the limits that can be reached in linear gradients but poorly in step gradients. Examples based on a conventional HETP of about 12 μm using a 5 μm particle packed column reveal that the best time compression factor that could be expected is twice the one predicted with an ideal column.