Ion chromatography, a form of liquid chromatography, measures concentrations of ionic species by separating them based on their interaction with a resin. Ionic species separate differently depending on species type and size. The ions in an eluent pass through a pressurised chromatographic column where ions are absorbed by column constituents, begin separating from the column. The retention time of different species and the continuous measurement of the eluent conductivity determines the ions and their concentrations in the sample.