In reversed phase HPLC, column deterioration causes poor peak shapes or reduced retention times. The column deterioration results from chemical alteration of  the packing material, such as loss of, for example, C18 bonded phase or dissolution of silica-gel as the base material. Such changes result in columns which are difficult to restore and reuse.

However, use of 100% aqueous mobile phase in an ODS column can sometimes result in steep reduction in retention times for compounds as in the figure below. Many may think the reduction of this retention time is due to the permanent column damage. But this is not always the case. Sometimes the cause is believed to be the decrease in the apparent hydrophobicity of packing material due to the polarity difference between the water in the mobile phase and the surface of the packing material bonded with C18 functional groups making it difficult to solvate the phase. Overcoming this and restoring the initial retention time is easily achieved by flushing the column with 10 times its volume of mobile phase containing 50% organic solvent. This effect is believed to be the result of the decrease in the repulsion between the eluent and the C18 functional groups. If the retention time reduction occurs when using 100% aqueous mobile phase, always try to flush the column with an organic solvent/ water mixture as described above to attempt to regenerate the column.

Column:		150 x 4.6 mm I.D.
Eluent:		20 mM KH2PO4-K2HPO4 (pH6.9)
Flow rate:		1.0 mL/min
Temperature:		37°C
Detector		UV at 254 nm