STATIONARY-PHASE DEGRADATION IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY - A POSSIBLE CAUSE OF BAD PREDICTIONS IN EXPERIMENTAL-DESIGN

The degradation in function of time of cyanopropyl- and octadecyl-modified silica stationary phases, a polymer coated silica phase and a polymer phase is investigated as this could be a cause of bad predictions in experimental design. By simulating routine conditions on both types of silica columns, considerable changes of retention, peak width and asymmetry in function of time were observed when switching mobile phase pH but also when mobile phase pH is held constant. The initial column performance was best maintained on the polymer coated silica column. On most of the other columns, changes in elution characteristics are rapid enough to make them a Major cause of bad predictions in experimental design.