CATION-EXCHANGE CHROMATOGRAPHY IN NONAQUEOUS SOLVENTS

Much of the selectivity of organic ions in conventional ion chromatogr aphy comes from hydrophobic interaction between the carbon chain of th e analyte ions and the polymer matrix of the ion exchanger. By operati ng in organic solvents containing little, if any, water, the true ion- exchange selectivity of various organic ions can be measured. Retentio n factors (capacity factors, k') for a series of protonated amine cati ons were measured in methanol, ethanol, 2-propanol and acetonitrile us ing a polymeric cation-exchange resin, conductivity detection, and elu ents of methanesulfonic acid in the same organic solvent. Plots of log t(R)' vs. log methanesulfonic acid concentration were linear with slo pes close to the theoretical slope of -1.0 except for acetonitrile whe re the slopes averaged -0.82. The retention factor showed little chang e with increasing carbon chain length in n-alkylamine cations, but inc reased substantially at fixed eluent concentration in going from metha nol, to ethanol, to 2-propanol and especially to acetonitrile. Several practical separations of organic amine cations were demonstrated in n on-aqueous media. One advantage of this technique is that neutral orga nic analytes elute very quickly in non-aqueous media and thus do not i nterfere with chromatographic separations of the ions.