RETENTION AND SELECTIVITY EFFECTS OF COATING OCTADECYLSILICA STATIONARY PHASES WITH LOW-MOLECULAR-WEIGHT ALCOHOLS IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY USING WATER AS MOBILE-PHASE

A simple but useful experimental method for observation of the effects of organic modifiers in the stationary phase in reversed-phase liquid chromatography (RPLC) is reported, An octadecylsilica (ODS)-packed co lumn, used before and after treatment with low molecular weight alcoho ls (methanol, ethanol, 1-propanol, and 1-butanol), was employed for an alysis of two groups of water-soluble model analytes by RPLC with mate r as the mobile phase. The first group was a mixture of 14 species of nucleosides and their bases and mas used to represent hydrogen-bonding analytes, whilst the second group was a mixture of seven alkylsulfona tes used to represent hydrophobic analytes, For both groups of analyte s, alcohol-modified ODS stationary phases gave higher resolution and a shorter retention time than untreated ODS, These differences in chrom atographic performance showed that the alcohol was adsorbed onto the s tationary phase and influenced the elution of the target analytes. The adsorbed alcohol is postulated to decrease the overall hydrophobicity of the stationary phase and also to introduce a hydrogen-bonding inte raction with suitable analytes, The resultant changes in retention and separation selectivity exhibited by the alcohol-modified stationary p hases are dependent on the relative magnitudes of these effects, This behaviour is illustrated using the two groups of target analytes.