Characterization of ion exchange functionalized cyclic olefin polymer open tubular columns

We describe both the cation-exchange (CEX) and anion-exchange (AEX) capacity measurements of functionalized cyclic olefin polymer (COP) open tubular (OT) columns. COP capillaries were sulfonated to provide CEX functionality and then coated with AEX latex to provide AEX functionality. We measure functionalization uniformity along the column by (a) separately measuring capacities of two halves of a column, (b) measuring retention factors for several ions in successive 10 cm segments of a column in multiple injections and (c) measuring retention variance of a single ion in different segments of a column from a single injection. Data were collected in both flow directions. Errors in CEX capacity determination arises primarily from uncertainties in titration end point location. AEX capacities are typically 10x higher, reducing the relative measurement error. In the AEX case, both titration end point location error and variations in column internal diameter contribute to the overall uncertainty. Although sulfonation of COP results in nonuniform CEX functionalization, AEX latex coating of this surface results in uniform AEX coverage. Frontal displacement chromatography (using both admittance and optical detection) and acid-base titrimetry were compared for capacity measurement. In a pooled standard deviation based t-test for the data on 8 columns, at the 95% confidence level, CEX capacity differed significantly between two halves of a column. But AEX capacity of AEX columns prepared by coating the same CEX columns with AEX latex did not.