TLC to Flash Optimization

TLC is used to determine optimum solvent compositions for flash chromatography. Since flow cannot be controlled, retention is measured in distance rather than time or column volume. The Retention Factor, Rf, is defined as the distance traveled and ΔRf is the distance between the compounds. A suitable solvent system is one that moves the compound to an Rf of 0.1 - 0.3 and will separate the compound from others by a ΔRf of at least 0.1. Unlike TLC, flash chromatography is governed by column volumes (CV). CV is the number of column volumes required to elute the compound from the column. ΔCV is the number of column volumes between the compounds. A suitable flash solvent system is one which elutes the compound in 3-6 CV and will separate compounds by a ΔCV greater than 1.

The loading chart below provides guidelines based on sample load and ΔCV to determine the appropriate sized column. The chart is based on using 50μ HC silica columns under normal phase conditions. Expect 2-3 times higher loading with 25μ and 15μ silica.

Interchim provides a wide variety of high performance TLC plates to match the column offering. To transpose a TLC run to a Flash run, the same type of silica/sorbent should be used for both techniques.