On-line Determination of Nitrite and Nitrate in sea-water by Flow Injection Analysis

Using copper cadmium to Flow Injection Analysis(FIA),It realizes that nitrate nitrogen and nitrite nitrogen's determination at the same time in water under the automatic conrtol of three-way valve.In hydrochloric acid,nitrite and sulfonamides forms diazo subsance,then coupling with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a roses red azo dyes,which has the larger absorption at 530 nm.Nitrate can be determinated after being reduced to nitrite by cadmium reducer column.The linear range of NO-2-N and NO-3-N are 2-50μg/L and 20-1000μg/L;the low limit detection are 0.33μg/L and 0.66μg/L;the relative standard deviation are 0.73% and 1.48%(n=8),respectively.And the determination rate is 16 h-1.It gets a satisfied result when the method applied to determinate NO-2-N and NO-3-N in varied sea-water samples,with recovery is 93.5%-111.0%.This method is simple,rapid and reproducible,so it can be applied in practical detection.