Resins and Columns for Ion Chromatography

Anion-exchange resins of variable but low exchange capacities are produced under mild conditions and short reaction times in the chloromethylation reaction. Conditions for the amination are chosen to convert as much of the chloromethyl group as possible to the quaternary ammonium chloride, although experience indicates that some of the chloromethyl remains unreacted. 

Depending on the conditions chosen, this procedure can produce anion exchangers with capacities from 0.005 to 0.16 mequiv g when using XAD-1 as a substrate. This range includes the capacities most useful in ion chromatography. 

A large variety of columns for IC is available. Particle size of the resin column packing has steadily decreased from about 10 gm to 5 gm, and now to 3 gm. Resins are spherical and have a narrow particle size range. Column lengths are typically 5, 10, 15 or 25 cm. Colurim diameter is generally 4.0-4.6 mm, although columns 2.0 mm in diameter are also available. 

Both anion- and cation-exchange columns are available with a choice of resin matrix (polymeric or sUica) and ionic functional group. Modem IC resins often contain imbedded polar groups in addition to the ion-exchange groups. The purpose is to reduce the hydrophobic nature of the soHd ion exchanger and to modify the nonionic attraction of analyte ions for the soHd phase. The effects of resin composition on anion selectivity will be discussed Section 3.4. 

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