Abstract: To enhance the conductivity detection sensitivity of the common anions (Na-anions) in the electrostatic ion chromatography (EIC) by elution with water, a conductivity enhancement column packed with a strongly acid cation-exchange resin in the H-form is inserted between the ODS-silica separation column modified with zwitterionic sufactan(CHAPS: 3-{(3-cholamidopropyl)-dimethylammonio}propanesulfonate) column and conductivity detector. Specifically, the Na-anion pairing is converted to H-anions paring after the EIC separation and then detected sensitively by conductivity detector. The effects of conductivity enhancement and suppression in the EIC by the enhanced conductivity detection is characterized for the common strong acid anions such as SO42-, Cl-, NO3-, I- and ClO4- and weak acid anions such as F-, NO2-, HCOO-, CH3COO- and HCO3-. For the conductivity enhancement effect in the EIC, it is found that the conductivity of measured for all strong acid anions (Na-anions) was enhanced according to the theoretical conductivity predicted for H-anions and that of measured for weak acid anions was suppressed depending on their pKa1 of H-anions. For the calibration linearity in the EIC, the strong acid anions were linear (r2 = 0.99–1.00) because the degree of dissociation is almost 1.0 over all the concentration range and that of the weak acid anions were non-linear because the degree of dissociation is decreased by increasing the concentration of the weak acid anions. In conclusion, the EIC by enhanced conductivity detection was recognized to be useful only for the strong acid anions in terms of conductivity detection and calibration linearity.

Key words: Common anion, Conductivity enhancement, Water eluent, Electrostatic ion chromatography