A novel turbidity compensation method for water measurements by UV/Vis and fluorescence spectroscopy

Abstract

The study presented here addresses the influence of turbidity on UV/Vis spectroscopy measurements of water bodies, a factor that affects the accurate identification and quantification of substances. The novelty of the developed turbidity compensation method is its applicability over the entire UV/Vis spectrum (250 – 900 nm), enabling the accurate detection of substances which appear in the UV/Vis spectrum at higher wavelengths (e.g. chlorophylls), and at high turbidity amounts. Commonly used approaches for turbidity compensation bases on the relationship before and after its correction through mapping functions or subtracting the turbidity-related absorbance from the original spectrum. However, these methods usually consider only certain wavelength ranges, such as 200 – 400 nm, and often reach limitations when applied to real water samples due to increase of turbidity. A significant improvement in our method was achieved by simultaneous determination of turbidity in the sample using scattered light measurement at 850 nm. This information was then applied to generate a turbidity-compensation curve, which was then used to correct the absorption spectrum according to Lambert-Beer’s law. The experimental results show that this novel method reduces the root mean square error (RMSE) from 0.5935 mg L–1 to 0.0218 mg L–1 of the rhodamine B predictions. For better comparability, COD measurements were also carried out and an RMSE of 0.3096 mg L–1 and an R2 of 0.979 were obtained. In summary, it corrects the absorbance deviation caused by turbidity, improves the accuracy of substance prediction and works even at low substance concentrations in turbid solutions or for realistic measurements.