Selectivity related to carbon loading and end-capping of octadecyl-bonded silica gels in reversed-phase liquid chromatography

Abstract

Four types of octadecyl-bonded silica gel were synthesized from the same silica gel and their chromatographic properties were examined by studying the retention behaviour of n-alkanes, alkylbenzenes, alkyl alcohols, halogenated benzenes and polyaromatic hydrocarbons. The packings were high-carbon (HIC)-loaded packings with and without end-capping (HIC-ODS-E and HIC-ODS-NE) and low-carbon (LOC)-loaded packings with and without end-capping (LOC-ODS-E and LOC-ODS-NE). Although the capacity ratios measured on the two LOC-ODS were smaller than those obtained on the two HIC-ODS, the retention behaviour of compounds on LOC-ODS-E was similar to that on HIC-ODS, including two other ODS packings (Hypersil ODS and Develosil ODS). The π-energy effect, defined as the influence of double bonds of solutes on the retention, calculated for polyaromatic hydrocarbons and alkylbenzenes was almost the same on all these packings. The energy effect of these hydrophobic compounds measured on LOC-ODS-NE was slightly different from that on the two HIC-ODS. LOC-ODS-E showed a small selectivity difference in the retention of aromatic and aliphatic compounds. LOC-ODS-NE showed a greater selectivity difference than others, but its lack of stability made it unsuitable for chromatographic purposes.