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The effects of conductivity detection temperature on calibration sensitivity and linearity in suppressed ion chromatography using hydronium or hydroxide eluent were investigated. Theoretical calibration curves for lithium and nitrate ions at 0–35 °C were calculated and compared with experimental data. As the detection temperature was lowered, both sensitivity and linearity of calibration at low concentrations were improved due to the reduced interference by water autoionization equilibrium; 4.3- and 1.3-fold increases in linear regression slopes were observed in the 0–1 µmol/L range when the temperature was lowered from 35 to 5 °C for lithium and nitrate, respectively, along with significant increases in the correlation coefficient. Any remaining water autoionization effect was near completely removed by using eluents contaminated with rubidium or bromide ion at 0.1 µmol/L.

and theoretical studies were conducted to investigate low and non-linear responses in sub-micro molar-level suppressed ion chromatography with a hydroxide eluent. A calculated response was derived using experimentally determined detector effluent ion composition data and compared with measured experimental responses. The calibration curve was non-linear, and its slope varied considerably with different instrumental setups and operating conditions. The non-linearity of the solution conductivity response was determined by two acid-base equilibria of water and carbonic acid, and fluoride ion. By using eluent contaminated with para-toluene sulfonate at micro molar level, the non-linear response was greatly alleviated.

Theoretical and experimental studies on nonlinearity of calibration in suppressed ion chromatography have been conducted. In suppressed cation chromatography with a strong acid as an eluent, nonlinear response in conductivity detection caused by water dissociation equilibrium shift has not been of concern in general. However, this issue can be of great consequence for analysis at the µg/L level. Theoretical calculation shows that the calibration curves at µg/L level are highly curvatured and a negative response range exists, making it impossible to make a determination. The extent of this phenomenon highly depends on the types and concentrations of ionic impurities present in the eluent. The presence of nonlinearity of calibration at the µg/L level is demonstrated experimentally. In order that linear calibrations are assured and negative response is eliminated, an addition of small amount of cation impurities into the eluent is recommended, as excessive amount tends to increase background conductance and their detection limits.