Rapid Correction of Turbidity Interference on Chemical Oxygen Demand Measurements by Using Ultraviolet-Visible Spectrometry

We developed a simple, rapid, and high-precision method to compensate for the turbidity interference in the measurement of water parameters using ultraviolet-visible spectrometry. By combining direct orthogonal signal correction (DOSC) with partial least squares (PLS), we corrected the full spectra (220 nm to 600 nm), significantly enhancing the accuracy of the water parameter calculations. First, DOSC was applied to filter out turbidity-related components, retaining only the spectral elements most closely associated with the target substance, without requiring a standard baseline for the turbidity effect. Then, 13 wavelengths were selected from the corrected full spectra to construct the discrete absorption spectra. Further, a PLS regression model was established based on the corrected discrete absorption spectra and their corresponding concentrations. In our experiment, this method effectively eliminated the blue shift and peak height reduction caused by turbidity, especially in shorter wavelengths, which are more sensitive to interference. Moreover, when applied to new samples, the correlation coefficients (R2) between the predicted and actual values improved from 0.5455 to 0.9997, and the root mean square error (RMSE) decreased from 12.3604 to 0.2295 after correction. Overall, the DOSC-PLS method, together with ultraviolet-visible spectrometry, posed a great potential for the precise monitoring of target water parameters in field studies.