Flow injection systems were combined with an inductively coupled plasma atomic emission spectrometer for the development of on-line enrichment and determination of trace amounts of S in High-purity Iron samples (obtained as Certified Reference Materials from the Iron and Steel Institute of Japan). An alumina microcolumn was used for the enrichment of sulfate and the removal of Fe. The properties of several types of alumina were compared. The effects of Fe, diverse elements and acids on the adsorption of sulfate were investigated. The detection limit (3σ) of S in High-purity Iron is 0.3 μg g-1. A standard additions method and two on-line standard additions methods were used for the determination. The possibility of S vaporization at the trace amount level is evaluated.