M. Aimoto et al., DETERMINATION OF TRACE AMOUNTS OF NITROGE N IN STEEL BY GAS-DIFFUSIONFLOW-INJECTION WAVE-GUIDE CAPILLARY CELL SPECTROPHOTOMETRY, Bunseki Kagaku, 45(2), 1996, pp. 193-199
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.