[Preparation and characterization of open tubular ion chromatographic columns]

In recent years, significant progress has been made in the area of open tubular ion chromatography (OTIC). In particular, gradient OTIC has been realized through the development of hydroxide eluent-compatible OTIC columns. This review covers the preparation and characterization of different OTIC columns, ranging from the historic silica-based columns to the newly emerging polymer-based open tubular (OT) columns. The preparation of various OTIC stationary phases, from grafted to latex agglomerated and monolayer to multilayer phases, has been briefly introduced. The characterization of electrostatic latex agglomerated OTIC columns has been extensively discussed, e. g. fluorescent ion displacement chromatography, frontal displacement chromatography, and frontal reaction chromatography have been used to measure the capacities of OT columns, and the results are compared with the theoretical calculation values. The variable α_iex, defined as the number of ion-exchange equivalents per unit surface area, is used as an indicator of the capacity of OT columns, to enable a straightforward comparison between OT columns having different inner diameters (i.d.). The newly introduced column capacity parameter, γ_iex, defined as the stationary phase capacity per unit liquid volume present, is used to investigate the relationship between packed and OT columns when using the same stationary phase. Methods for improving the column efficiency, such as decreasing the column diameter and/or increasing the column temperature, are presented. In addition, determination of the functionalization uniformity along an OT column by (a) separately measuring the capacities of two halves of the column, (b) measuring the retention factors for several ions in successive 10 cm segments of the column in multiple injections, and (c) measuring the retention variance of a single ion in different segments of the column from a single injection, is discussed.