Single-column anion chromatography with indirect uv detection using pyromellitate buffers as eluents

Abstract

Ion chromatography can be conveniently carried out with conventional high-performance liquid chromatographic equipment and classical ion exchangers using a single column and a UV-absorbing eluent ion. Solute peaks are detected as vacancy peaks (corresponding to a decrease in eluent absorbance). Benzenepolycarboxylate buffers such as those obtained from pyromellitic acid are used as eluents for anion analysis; owing to the four carboxylic acid groups, the eluent ion charge varies with pH, and the eluting power can be adjusted within a wide range. A linear relationship holds between the logarithm of the solute capacity factor and the logarithm of the concentration of the eluting species; the slope observed is - x/y, here x and y are the charges on the solute and eluent anion, respectively. At a constant analysis time, the best sensitivity is achieved when the initial absorbance of the eluent (determined by the detection wavelength) is high but its concentration is low, and therefore its charge is high enough to give the required eluting power. Within the linearity range, quantitative analysis requires only one calibration graph when peak-area measurements are performed. The detection limits are about 2–5 ng injected and compare favourably with other detection modes, considering the simplicity of the method. Various examples of separations of inorganic and organic anions are given.