2-DIMENSIONAL CONDUCTOMETRIC DETECTION IN ION CHROMATOGRAPHY - POSTSUPPRESSOR CONVERSION OF ELUITE ACIDS TO A BASE

A converter, consisting of a serially connected cation-exchanger and an anion-exchanger membrane tube, woven in a low dispersion configuration and bathed externally with NaOH, can convert an eluite acid HX (with varying degrees of efficiency, depending on the pK of HX) to NaOH. Such a converter is installed after the conductivity detector of a conventional NaOH eluent suppressed ion chromatography system and followed by a second conductivity detector. The two dimensional response data readily reveal peaks due to weak and very weak acids hidden in the suppressed baseline or overlapped with strong acid eluite peaks. The sensitivity for strong acid analytes generally decrease by a factor of approximately 2 for the converted signal vs the suppressed ion's signal whereas for a weak acid analyte, depending on the pK, concentration, and the number of protons involved, the converted signal can be more than 1 order of magnitude greater. The method allows an estimation of the pK of the eluite peak and permits approximate quantitation without standards. Numerical simulations of a theoretical model of the process are presented and compared with experimental results.