Stepped gradients on polymeric monolithic columns by photoinitiated grafting.

The surface of polymethacrylate monoliths was functionalized by a post-polymerization modification, by means of a novel photo-initiated graft procedure where the charged monomer, sulfopropyl methacrylate, was controllably grafted stepwise, i.e. with incremental graft energies. The grafting approach was optimized using scanning capacitively coupled contactless conductivity detection. The effect of the localized ion exchange capacity and resultant gradient stationary phase upon ion-exchange chromatographic retention, selectivity, and performance was investigated, and compared to a homogeneously grafted (isotropic) column. The gradient column provided reduced peak widths at half height for both cationic analytes, with a reduction of 34 and 33%, respectively, when compared to the isotropic column.