Comparison and characterization of reversed phases

Summary A pragmatic test procedure for comparison and evaluation of reversed phases is described. The differences in retention between RP8 and RP18 can be compensated for by adjustment of the eluent composition. A 10% increase in the water content doubles the k values, as does the exchange of an RP8 with an RP18 column. It is possible to differentiate between the two columns with the pair ethylbenzoate and toluene. Under stand-ard conditions (methanol-water, 55–45, v/v; 49–51, w/w) with RP8 ethylbenzoate is always eluted together or after toluene, whereas with RP18 it is always eluted in front of toluene.With the same eluent composition the suitability of stationary phases for the separation of basic solutes can be evaluated. With good phases—symmetrical peaks for basic solutes—aniline is always eluted before phenol and the peak asymmetry relationship of the aniline and phenol peak is less than 1.3. With such good stationary phases the retention of bases is independent of sample size if the linear capacity of 0.1 mg sample/g stationary phase is not exceeded. The test can also be used to study column stability towards hydrolysis.