Method optimization of hydrophilic interaction chromatography separation of nucleotides using design of experiment approaches I: Comparison of several zwitterionic columns.

A systematic method in hydrophilic interaction chromatography (HILIC) was developed for the separation of four monophosphate nucleotides using design of experiment (DOE) approaches. Three HPLC parameters, the buffer concentration (ammonium acetate concentration), gradient time, and temperature, were evaluated within the quality design framework, and the effects on chromatographic parameters were investigated. Four zwitterionic columns (ZIC-HILIC, ZIC-cHILIC, NUCLEODUR HILIC, and PC HILIC) were used to separate four nucleotides, and the HPLC conditions for each column were successfully optimized, although PC HILIC did not give peaks that were suitable for optimization. In addition, it was proved that optimized HPLC conditions differed from column to column even when the same types of zwitterionic sulfobetaine-functionalized columns were applied. This tendency was explained by differences in the separation characteristics of each column, the thickness of the water-enriched layer on the surface of the silica supports, and the pH. DOE for development of the HPLC method provides an effective explanation of the interactions among the variable parameters, especially in HILIC mode. Finally, a robust analytical method could be established by setting the optimum parameters. Among the employed columns, ZIC-cHILIC provided the widest range of suitable analytical conditions. NUCLEODUR HILIC was difficult to build a robust analytical method since the elution order of cytidine monophosphate and guanosine monophosphate was reversed.