2-DIMENSIONAL CONDUCTOMETRIC DETECTION IN ION CHROMATOGRAPHY - SEQUENTIAL SUPPRESSED AND SINGLE COLUMN DETECTION

A novel approach to simultaneously practicing both suppressed and nonsuppressed ion chromatography (IC) is proposed. Following the detector of a conventional NaOH eluent suppressed IC system, a constant concentration of NaOH is introduced by an in-line microelectrodialytic NaOH generator, and this is followed by a second conductivity detector. The second detector background is typically maintained at a level of 20-30 mus/cm (corresponding approximately to 0.1 mM NaOH), and the detector output is the same as what would be observed in a single column mode with a low concentration NaOH eluent. Together, the two detector outputs provide detectabilities at the microgram per liter level across the pK(a) range-from fully dissociated to very weak acids (up to pK(a) 9.5). Excellent linearity of response is observed, and the system provides qualitative information about peak purity and eluite pK(a). In addition to the usual ratio plots, it is suggested that multidimensional detection in any separation system is best served by plotting the raw detector outputs against each other.