DETERMINATION OF TRACE AMOUNTS OF NITROGE N IN STEEL BY GAS-DIFFUSIONFLOW-INJECTION WAVE-GUIDE CAPILLARY CELL SPECTROPHOTOMETRY

We designed a new, simple and precise continuous-flow type analytical method for nitrogen determination combining flow injection analysis (F IA) and waveguide capillary cell (WCC) spectrophotometry. We used a ga s-diffusion FIA system for sample preparation and introduction. We pre pared steel solution decomposing steel sample with hydrochloric acid. First, nitrogen forms NH4+ in solution changes into NH3 gas in strong alkaline media. Only NH3 gas is separated from the matrix through poro us Teflon membrane tubing. Finally, an indophenol type blue dye is pro duced by the reaction of NH3 gas and some color-producing reagents for spectrophotometric detection. As the detector, we applied the WCC spe ctrophotometer. A 50 cm long WCC enhances the sensitivity about 50-tim es compared with a 1 cm conventional cell. By this method, the analyti cal results of nitrogen determination in four certified reference mate rials conformed well with the certified values. The variation for 2 mu gN per g steel was about 3% (n=3). Moreover comparing the analytical results of the proposed method with those of the conventional (JIS) me thod by using two steel sample, we found good agreement.