Universal anion detection by replacement-ion chromatography with an atmospheric-pressure solution-cathode glow discharge photometric detector

A new method of detection for ion chromatography (IC) is described that couples replacement-ion chromatography (RIC) with an atmospheric-pressure solution-cathode glow discharge (SCGD). In the new instrument, a conventional suppressed IC arrangement is followed by a "replacement column" that consists of a cation-exchange micromembrane suppressor continuously regenerated with Li₂SO₄. In this arrangement analytes are stoichiometrically converted to Li salts when they pass through the replacement column and are introduced into the SCGD, where they are detected indirectly by atomic emission spectrometry. Though found to be unsuitable for cation determinations, the SCGD-RIC instrument shows good repeatability (<3.5% peak area relative standard deviation), approximately 4 orders of linear dynamic range, universal calibration (similar molar sensitivity for anions of the same charge), and detection limits between 0.08 and 0.64 μg·mL^-1 (25-μL injection) for several mono- and divalent anions. Deviations from the universal calibration were also observed and are critically evaluated. Optimal operating conditions are described, analytical figures of merit are presented, and background sources present in the system are characterized and explained.