PURPOSE: To enable quantitative analysis of NO2- by an ion chromatography by subjecting a removal column to a pretreatment wherein a soln. contg. NO2- ion is passed therein thereby decreasing the change in peak height with respect to the amt. of the NO2- ion with time in the stage of analyzing.

CONSTITUTION: A pretreatment of a removal column simultaneously with the regeneration thereof can be accomplished simply by adding a chemical contg. NO2, such as NaNO2, nitrous acid water or the like, to an acid of 1 normal, such as sulfuric acid, nitric acid, hydrochloric acid, or the like, which is a regenerating liquid, and passing the liquid through the column to be treated. If the amt. of the above-mentioned chemical to be added is too much, a large amt. of gaseous NO is generated and the regeneration of the removal column is infeasible. If the amt. is too little conversely, the effect of the treatment is poor and therefore a range of 0.01W0.1mol concn. is preferred with NaNO2. The treatment after the regeneration can be accomplished simply by running an aq. soln. of NaNO2, etc. through the regenerated removal column. If the removal column treated in the above-mentioned way is used, the change in the conductivity peak of the NO2- ion with time is suppressed and the quantitative analysis of said ion together with other anion is made possible.