PURPOSE: To perform the quantitative analysis of an ion to be measured with high sensitivity in good reproducibility, in chromatographic analysis, by bringing deionizing apparatus made of an ion exchange membrane into contact with a specific electrolyte solution while treating said electrolyte solution with a same type insoluble ion exchange substance to efficiently remove an opposite polarity ion.

CONSTITUTION: The specimen solution from a speciment injection apparatus 1 is injected into the liquid stream from an eluate sump 6 and the resulting mixture is passed through a deionizing apparatus 2 made of an ion exchange membrane while the componential component therein is removed by a separation column 2. The apparatus 2 is immersed in, for example, an aqueous solution containing about 0.01N of a N+ type high-molecular electrolyte such as polystyrene sulfonate with M.W. of 500 or more when an ion to be measured in a container 11 is an anion and immersed in an aqueous OH- type high-molecular electrolyte solution 13 when the ion to be measured is a cation while an insoluble H+ type or OH- type ion exchange substance 14 is preliminarily put in the container 12 and stirring is performed by a sirrer 15 to efficiently remove an ion component having polarity opposite to that of the ion to be measured in the tube 12. By this method, the long-term continuous use of the apparatus 3 is enabled and quantitative analysis is enabled with high sensitivity in good reproducibility.