# Advances on Water Quality Detection by UV-Vis Spectroscopy
## 4 Research Status and Progress of Main Water Quality Parameters
### Research on the Detection of Nitrate Nitrogen in Water  
Nitrate nitrogen is an important indicator to reflect the degree of water pollution. Increasing amounts of nitrogen-containing compounds are being discharged into the environment [58]. If the discharge exceeds the standard, the balance of the water body will be destroyed, resulting in rapid algae and plankton growth in the water body. The decrease in concentration and the death of fish and shrimp in a large area will eventually worsen the water quality, thus affecting human production activities in the ocean [59].  
[PERSON] et al. [60] obtained the predicted concentration of nitrate by fitting the corrected concentration and absorbance of nitrate with the PLS method. [PERSON] et al. [61] proposed a fast quantitative prediction method to determine the nitrate concentration in water by combining UV spectroscopy with the partial least squares support vector machine (LS-SVM) model, and the prediction accuracy of the model was significantly improved. [PERSON] et al. [62] used the PLSR model established by using wavelet transform, first-order differential, and SPA to predict the effect very effectively, as it can quickly and accurately determine the total nitrogen content in water.  
Because the UV absorption peaks of nitrate nitrogen and nitrite nitrogen are very close, and the UV absorption curves overlap significantly, mutual interference is not conducive to the determination of their concentrations. [PERSON] et al. [63] combined UV-Vis spectrophotometry with the second-order differential method to solve the problem of serious overlapping of absorption spectra of nitrite nitrogen and nitrate nitrogen. The rapid determination of nitrite nitrogen and nitrate nitrogen in samples was realized. Turbidity can reflect the degree of obstruction caused by the solution when light passes through it, and it includes the reflection of light suspended by the solution and the absorption of light by solute molecules. Turbidity is not only related to the content of suspended matter, but also its shape, size, and refractive index. In the detection of nitrate-nitrogen by using UV-Vis spectroscopy, due to the scattering effect of suspended matter in water, the absorption spectrum will change significantly, which will cause a large error in the measured modeling data, resulting in an inaccurate detection result.  
[PERSON] et al. [64] proposed a method of nitrate concentration measurement based on the first derivative of the UV absorption spectrum, which can reduce turbidity interference, to improve the accuracy of rapid detection of nitrate content by using the UV spectrum. [PERSON] et al. [65] analyzed the influence of formalin turbidity standard solution on the UV absorption spectrum of a nitrate nitrogen standard solution. Based on this, a turbidity compensation method for the compensation curve method was proposed to compensate and correct the UV absorption spectrum of nitrate nitrogen, and the method was verified by using experiments; the RMSE of the prediction set was 0.124.