Process water from flue gas desulfurization mainly contains sulfite and sulfate. Besides these two main components, other sulfur species may be formed in the process. This application describes the determination of such late-eluting sulfur species with ion chromatography applying a Dose-in gradient. The applied gradient profile enables the resolution of amidosulfonate, dithionate, and imidodisulfonate besides thiosulfate, thiocyanate, major anions, and acetate.