Probing the kinetic performance limits for ion chromatography. I. Isocratic conditions for small ions

The first use of the kinetic plot method to characterise the performance of ion-exchange columns for separations of small inorganic anions is reported. The influence of analyte type (mono- and divalent), particle size (5 and 9microm), temperature (30 and 60 degrees C) and maximum pressure drop upon theoretical extrapolations was investigated using data collected from anion-exchange polymeric particulate columns. The quality of extrapolations was found to depend upon the choice of analyte, but could be verified by coupling a series of columns to demonstrate some practical solutions for ion chromatography separations requiring relatively high efficiency. Separations of small anions yielding 25-40,000 theoretical plates using five serially connected columns (9microm particles) were obtained and yielded deviations of <15% from the kinetic plot predictions. While this approach for achieving high efficiencies results in a very long analysis time (t(0)=21min), separations yielding approximately 10,000 theoretical plates using two serially connected columns (t(0)<5min) were shown to be more practically useful for isocratic separations when compared to use of a single column operated at optimum linear velocity (t(0)>10min).