Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710119, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Molecules. 2022 Dec 28;28(1):250. doi: 10.3390/molecules28010250.
To solve the problem that turbidity in water has a significant effect on the spectra of nitrate and reduces the accuracy of nitrate detection, a turbidity-compensation method for nitrate measurement based on ultraviolet difference spectra is proposed. The effect of turbidity on the absorption spectra of nitrate was studied by using the difference spectra of the mixed solution and a nitrate solution. The results showed that the same turbidity had different effects on the absorbance of different concentrations of nitrate. The change in absorbance due to turbidity decreased with an increase in the nitrate concentration at wavelengths from 200 nm to 230 nm, although this change was constant when the wavelength was greater than 230 nm. On the basis of this characteristic, we combined the residual sum of squares (RSS) and interval partial least squares (iPLS) to select wavelengths of 230-240 nm as the optimal modeling interval. Furthermore, the turbidity-compensation model was established by the linear fitting of the difference spectra of various levels of turbidity. The absorption spectra of the nitrate were extracted by subtracting the turbidity-compensation curve from the original spectra of the water samples, and the nitrate concentration was calculated by using a partial least squares (PLS)-based nitrate-prediction model. The experimental results showed that the average relative error of the nitrate predictions was reduced by 50.33% to 1.33% by the proposed turbidity-compensation method. This indicated that this method can better correct the deviation in nitrate's absorbance caused by turbidity and improve the accuracy of nitrate predictions.
为了解决水中浊度对硝酸盐光谱有显著影响，从而降低硝酸盐检测精度的问题，提出了一种基于紫外差分光谱的硝酸盐浊度补偿测量方法。通过混合溶液和硝酸盐溶液的差分光谱研究了浊度对硝酸盐吸收光谱的影响。结果表明，相同的浊度对不同浓度硝酸盐的吸光度有不同的影响。在 200nm 到 230nm 波长范围内，由于浊度引起的吸光度变化随硝酸盐浓度的增加而减小，尽管在波长大于 230nm 时，这种变化是恒定的。基于这一特性，我们结合残差平方和（RSS）和区间偏最小二乘法（iPLS），选择 230nm-240nm 作为最佳建模区间。此外，通过对不同浊度水平的差分光谱进行线性拟合，建立了浊度补偿模型。通过从水样的原始光谱中减去浊度补偿曲线，提取硝酸盐的吸收光谱，并使用基于偏最小二乘（PLS）的硝酸盐预测模型计算硝酸盐浓度。实验结果表明，所提出的浊度补偿方法可将硝酸盐预测的平均相对误差从 50.33%降低到 1.33%。这表明该方法可以更好地校正浊度引起的硝酸盐吸光度偏差，提高硝酸盐预测的准确性。
