A comparison of the chromatographic properties of silica gel and silicon hydride modified silica gels

The retention properties of a silica gel column and a type C silica (silicon hydride) column for bases, sugars and polar acids were compared in hydrophilic interaction chromatography (HILIC) mode with formic acid or ammonium acetate as aqueous phase modifiers. The type C silica column was much more retentive for a series of model bases than the silica gel column and, surprisingly, retention of bases increased on the type C silica column when, the higher pH, ammonium acetate containing mobile phase was used. The retention of sugars was greater on the type C silica column than on the silica gel column and also increased on the type C silica column with increased pH suggesting either a silanophilic mechanism of retention or some unknown mechanism. Three type C silica based columns, type C silica, cogent diamond hydride and a β-pinene modified column, which it was hoped might exert some additional stereochemical discrimination, were tested for metabolomic profiling of urine. In general the unmodified type C silica column gave the strongest retention of the many polar metabolites in urine and could provide a useful complement to established HILIC methods for metabolomic profiling.