Retention of Neutral Solutes in Capillary Electrochromatography

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Abstract
The retention mechanisms of neutral solutes were compared between electrically driven chromatography and pressure driven chromatography. The entropies of solute transfer from a mobile phase to a stationary phase were more negative in electrically driven chromatography than in pressure driven liquid chromatography. These differences can be attributed, in part, to the generation of heat which occurs during electro-driven chromatography and which causes significant differences between the set and the actual column temperature. Retention factors in electrochromatography are affected significantly by changes in electric field strength. These variations can be minimized by performing the experiments at elevated column temperatures. For example, when the column temperature was increased from 293 K to 333 K, the RSD for pentachlorobenzene was lowered from 7.3 % to 4.3 %. In addition the analysis time was shortened by approximately 45 %. Due to the critical effect of temperature on separation in electrochromatography, it is imperative that the column temperature be kept constant and measured accurately.