VDM Marion, S: The Effect of Silica Surface Chemistry in RP-LC o

Chromatographic results from four, neutral steroids highlight the repeatable chromatography achieved on Spherisorb ODS1 phase and the non-repeatable chromatography expressed on Spherisorb ODS2 phase, with respect to retention, resolution and analyte selectivity of three keto steroids and ethinyl estradiol, a phenolic steroid. The significant differences between the two phases are that ODS2 contains a higher percent carbon load and ligand coverage, as a result of endcapping. A noteworthy and significant property of the silica component used as substrate, which is known as "type A" silica, contains high levels of metal impurities. It was shown to be inherently variable from batch to batch of the silica gel lot used for the stationary phase material. Experiments were designed to characterize the chelating potential,hydrophobicity, steric selectivity, hydrogen bonding potential and ion-exchange behavior of each phase. This work represents an attempt to determine a solute-to- stationary phase interaction that is the most likely cause for ODS2 phase chromatographic irreproducibility with the four component steroid test solution.