近红外光谱透射法测量废水化学需氧量(COD)的光程选择

PATHLENGTH SELECTION OF DETERMING THE CHEMICAL OXYGEN DEMAND(COD) IN WASTEWATER BY USING NEAR-INFRARED TRANSMISSION SPECTRA

在用近红外光谱法测量废水化学需氧量（COD）时,水是一个强干扰因素,如何选择合适的光程长以提高测量灵敏度,减少测量误差很重要.本文通过在傅里叶变换近红外光谱仪上用透射光谱法测量废水COD实验来讨论废水测量的光程选择.采集了60个养猪废水水样,分别用1mm、2mm、5mm和10mm的样品池作对比研究,用PLS回归建模,比较不同光程长对废水COD预测的效果,结果显示在800-1350nm谱区选用10mm的光程,在1350-2500nm谱区选用1mm或2mm的光程测量,使用双光程组合方法建模可以提高模型在800-2500nm谱区的预测性能.该光程组合方法对其它复杂组分的水溶液的近红外定量测量也具有一定的参考意义.

The chemical oxygen demand （COD） in wastewater can be determined by near-infrared spectra （ NIRs）, however it is strongly influenced by the water absorbance. It is then very important to choose proper pathlength for improving measurement sensitivity and thus minimize the measurement error. In this study, we presented a series of experiments to determine the optimum pathlength for COD determination using a Fourier transform near infrared instrument with transmission measurement. Sixty wastewater samples for this study were collected from hoggery. Partial least squares （PLS） models were developed based on the spectral data which had been collected by using the cell pathlength of 1 mm, 2mm, 5mm, and 10mm. The performances of the differents models were compared. The results show that the pathlength of 10mm developes the optimal performance in the spectral range 800-1350nm and that of lmm or 2mm of pathlength can be obtained in the spectral range of 1350- 2500nm. In addition, our results suggest that two pathlength combination can improve the reliability and accuracy of the model in the region of 800 - 2500nm. This method of two pathlength combination may also be applied to the quantitative analysis of complex components in aqueous solutions.