The effect of column packing procedure on column end efficiency and on bed heterogeneity – experiments with flow-reversal

The effect of column end structure and bed heterogeneity of six commercially available reversed-phase chromatographic columns for fastliquid chromatography with different column packing materials – such as fully porous (Waters XBridge C18 with 1.7 m particles) and superficially porous (Waters CORTECS C18 with 1.6 m particles), with column dimension of 2.1 × 50, 100 or 150 mm were tested with flow-reversal method. Themethod includes arresting theflow when a non-retainedmarker (thiourea) has penetrated to a given distance into the column and then reversing the column. Hence, when the flow has been restarted, the sample is eluted at the same end of the column where it entered. The experiments showed that all columns are axially heterogeneous, and some differences could be observed between the two respective column ends. Furthermore, we can conclude that the shorter columns are axially more homogeneous than the longer ones, thus the column length is an influencing factor on the column packing procedure