Study on the Determination of Nitrate with UV First DerivativeSpectrum under Turbidity Interference

The standard solutions of formalazid (5、10、15、20、25、30NTU), sodium nitrate (0.5、1、2、3、4、5mg/L), kaolin (10、30、50mg/L) and potassium nitrate (0.5、1、2、3、4、5mg/L) were prepared in the laboratory. UV2550 spectrophotometer was used to measure the absorption spectra of formazide solution, sodium nitrate solution and their mixed solutions in the wavelength range of 190-300nm. The absorption spectra of different solutions were processed with Origin Software for the first derivative, and the spectral characteristics of turbidity and nitrate ultraviolet absorption of the first derivative were compared. The wavelength range of 220-230nm was selected as the spectral analysis interval, and 30 different concentrations of mixed formalazide and sodium nitrate solutions were used as training samples. The partial least squares quantitative analysis model of nitrate was established on Matlab Software. UV2550 spectrophotometer was used again to measure absorption spectra of kaolin solutions, potassium nitrate standard solutions and their mixed solutions in the wavelength of 190-300 nm, and the obtained absorption spectra were processed with the first derivative by Origin Software. The established partial least squares model was used to predict the nitrate concentrations in the mixed solutions of kaolin and potassium nitrate.