Two-Dimensional Conductometric Detection in Ion Chromatography. Analyte Identification, Quantitation of Very Weak Acid Anions, and Universal Calibration

Abstract

A universal and sensitive detection method for anion chromatography is described. Following suppressed conductometric detection carried out with an NaOH eluent and an electrical suppressor, the eluite is transported through a microscale electrodialytic NaOH generator and a second conductivity detector. While the first detector responds primarily to strong acid anions, the second detector records a decrease in the NaOH background signal, regardless of the pK a of the analyte. Routine detection of very weak acids at the low micromolar level is possible. The dual detection method not only constitutes the most generally applicable approach to IC by combining the detection merits of both suppressed and single-column IC, it provides possibilities of peak identification beyond retention characteristics. Area ratio values from the two detector signals provide unique signatures for each analyte ion. It is possible to estimate the limiting equivalent conductance of an unknown eluite and the analyte concentration without specific calibration. The method is also effective in diagnosing the occurrence of coelution.