Application of an improved column characterisation system to evaluate the within and between batch variability.

The selection of a reversed-phase liquid chromatographic column with suitable selectivity for a particular separation is difficult if the brand name of the column is not known. A project to develop a chromatographic test procedure to characterize reversed-phase liquid chromatography C18 columns was started earlier and resulted in a fast, simple, repeatable and reproducible test procedure using four column parameters. Here, this procedure is used to evaluate the diversity of columns originating from the same batch as well as from different batches. The determination of one of the parameters, the retention factor of 2,2'-dipyridyl, was improved and a simplified test procedure is proposed.

Effect of long-term storage and use on the properties of reversed-phase liquid chromatographic columns.

In order to study column deterioration as a result of long-term storage and/or usage in liquid chromatography analyses, 55 pairs (same batch) of different commercial reversed-phase C(18) columns were examined using an already existing column characterisation system. After initial testing, one column was stored and the other was used to analyse different pharmaceuticals. All columns were characterized by four chromatographic parameters reflecting hydrophobicity, silanol activity, metal impurity and steric selectivity at the beginning and at the end of the test. An F-value was calculated to express the change of column properties with one single number. After performing analyses, higher F-values were obtained as compared to the non-used, stored columns. Although the time during which the columns were used to perform analyses was relatively short, an obvious influence was noticed, mainly resulting from small changes in silanol activity and hydrophobicity. Most of the affected columns have no endcapping and/or no base deactivation, making them more vulnerable for degradation, resulting in higher silanol activity and faster ageing. This effect is observed less with columns equipped with polar-embedded groups and/or polar endcapping, protecting the column by blocking the silanol groups and attracting a shielding water layer. Also columns with higher coverages and bulky or long chains show more resistance towards degradation.