Provided is a process of separating carboxylic acids comprising (a) providing an aqueous solution comprising (i) one or more mono-carboxylic acids, (ii) one or more di-carboxylic acids, and (iii) one or more tri-carboxylic acids, and (b) passing the aqueous solution through a collection of resin particles, where the resin particles comprise covalently bound quaternary ammonium groups, and wherein the collection of resin particles has uniformity coefficient of 1.5 or less.