SIMPLE AND RAPID-DETERMINATION OF MICRO-A MOUNTS OF NITROGEN IN STEELBY FIA METHOD USING GAS-DIFFUSION SEPARATION AND SPECTROPHOTOMETRIC DETECTION TECHNIQUES

An FIA system is presented for the simple and rapid determination of m icro amounts of nitrogen in steel; the system consists of a direct on- line coupling of pas diffusion separation of ammonia and subsequent sp ectrophotometric detection. During transport of the steel sample solut ion, which is prepared by decomposition of the steel sample with hydro chloric acid, to a separation unit by the carrier stream, NH4+ is conv erted to NH3 in strong alkaline media. In the separation unit, NH3 dif fuses through a porous PTFE membrane tubing, while a large amount of i ron matrix masked with tartaric acid remains in the outer carrier solu tion. The NH3 reacts with hypochlorite (NaOCl) in the inner stream. Wh en this hypochlorite solution containing the reaction product with NH3 merges downstream with 1-naphthol solution, indophenol blue dye is fo rmed and measured spectrophotometrically at 732 nm. The analytical res ults of certified reference materials obtained by the proposed method agreed well with the certified Values and showed good precision. As li ttle as 2 mu g/g nitrogen in steel can be determined and the analytica l readout is available within 5 min after injection of the steel sampl e solution. The complicated distillation process for pre-separation of ammonia from the iron matrix which is necessary in conventional chemi cal analysis of steel can be successfully avoided. It is notable that the proposed method is carried out in a continuous and almost closed s ystem without requiring any manual operation, and is simple, rapid as well as precise determination.