SIMPLE AND RAPID-DETERMINATION OF MICRO-A MOUNTS OF NITROGEN IN STEELBY FIA METHOD USING GAS-DIFFUSION SEPARATION AND SPECTROPHOTOMETRIC DETECTION TECHNIQUES
M. Komoda et al., SIMPLE AND RAPID-DETERMINATION OF MICRO-A MOUNTS OF NITROGEN IN STEELBY FIA METHOD USING GAS-DIFFUSION SEPARATION AND SPECTROPHOTOMETRIC DETECTION TECHNIQUES, Bunseki Kagaku, 44(9), 1995, pp. 725-730
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.