Derivative-ratio Derivative Ultraviolet Spectro-photometry For Simultaneous Determination Of Nitrate And Nitrite In Water

Nitrate and nitrite are widely existed in soil, water and foods. Nitrite is importantformer body of N-nitrosamine, which is a carcinogen. Excessive nitrate may causedenaturalization sanguineous albumen increasing in blood of children. Therefore,determination of nitrate and nitrite concentration is one importance item ofenvironment supervision.At present, there are many directly spectrophotometry to multicomponentwithout any separation, which is mainly combine chemometrics and use derivativeexport, such as dual-wavelength method, multiple liner regression methods, partialleast square, flow injection and pH gradient technique, derivative spectrum method,ratio spectra and derivative spectrophotometric. However, these techneques basicallyused first derivative, and did not involve second derivative. Derivative-ratio derivativespectrophotometry can treat this problem.In this paper, the principle of derivative-ratio derivative has been used. Themathematic model has been set up for determination of nitrate and nitrite in watersimultaneously. The maximum absorption wavelength is 200nm for nitrate,210nm fornitrite. Results indicate that maximum ultraviolet absorption wavelength of nitrate andnitrite change at pH<5 or pH>8. Therefore, acidity of determining nitrate and nitrite inwater simultaneity should be controlled between pH 5～8.Derivative-ratio derivative spectrophotometry of nitrate and nitrite bedeterminated with differential interval factor. The wavelength is 5nm, 10nm and20nm.When differential interval factor is 10nm, nitrate and nitrite could get morefitting absorption value between 195～230nm. As the maximum wavelength is 200nmfor nitrate, 210nm for nitrite, 200nm,210nm and 220nm is set in this experiment.When nitrite/nitrate is 50 ～ 1/50(molar ratio), and nitrite (or nitrate)concentration is 0.2mg/L, the analytical maximum relative error is 20 percent. Thenitrate linear range is 0 ～ 10mg/L, equation of linear regression isA′=-0.2657C-0.0207, linear regression coefficient R2=0.9998. The nitrite linear rangeis 0～13mg/L, equation of linear regression is A′=0.1689C-0.0154, linear regressioncoefficient R2=0.9996. The detection limitation for nitrite and nitrate is 0.017mg/Land 0.005mg/L respectively. Recovery rate is nitrate 98～105%,nitrite 95～103%.The interference experiments have been made forK+,Na+,Ca2+,Mg2+,SO42-,Cr3+,Al3+,Fe3+,Cu2+,Cl-,I-,NH4+,CO32-,and turbidity etc.Results indicate that K+,Na+,Ca2+,Mg2+,SO42-,Cr3+,Al3+ etc. without ultravioletabsorption between 195 ～ 230nm,and have no inference to nitrate and nitritedetermination. But Fe3+,Cu2+,Cl-,I-,NH4+,CO32-and turbidity have some effect. Themaximum concentration of these interfering materials is NH4+(100 mg/L),Cl-(60mg/L),Cu2+(10 mg/L),CO32-(10 mg/L),Fe3+(2mg/L),I-(2mg/L) and turbidity(30 degree).The nitrate and nitrite in water sample from Beijing North Rive effluentdisposal factory be determined by using this method. The analytical resultscorrespond to value by using national standard method(GB7480-87,GB7493-87).Thus, the method established in this paper for simultaneous determination of nitrateand nitrite is simple, accurate and credible.