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. (C) 2008 Elsevier B.V. All rights reserved.