Widespread proliferation of liquid chromatography-mass spectrometry (LC/MS) analysis has made LC/MS-compatible solvents, reagents, and analytical columns commercially available. For the analytical columns, highly versatile octadecyl-silica gel (ODS, C18) is mainly used. However, ODS has difficulty in separating a particular type of analytes (for example, highly polarized substances and basic substances represented by drugs and drug metabolites), even using aqueous mobile phases with low-eluting capability or ion-pair reagents. To overcome such difficulty, unmodified silica gel columns (HILIC columns) were proposed as useful options. After the unmodified silica gel columns were confirmed to be useful, we have developed Wakopak^® Wakosil-II 5SIL-AQ, column for analysis of highly polarized substances (Vol.74 No.1, Wako Junyaku Jiho (2006)).

This report presents an application example of Wakopak^® Wakosil-II 5SIL-AQ to analysis on "tiamulin" and "robenidine", which did not exhibit satisfactory peak shapes in ODS column. The application produced favorable results (Figures 1 and 2).

Compared with the ODS column, Wakopak^® Wakosil-II 5SIL-AQ exhibited drastically improved peak shapes and recovery rates and achieved separation under a mobile phase condition (using acetonitrile and volatile acid) compatible with LC/MS analysis, which can be advantage in comprehensive analysis of veterinary drugs. This report is thus posted with the hope that it would help those who involved in such analytical operations.