Concentration Determination of Pollutants in Water Using Ultraviolet Spectrophotometry and Partial Least Squares Method

Abstract

During the production of Phenylethylamine (PEA), NaOH is usually used as a reactant, and NaCl is produced. In the final product. Finally, the mixture including these three components is discharged into water and bring serious pollution to the water quality. So it is of great practical significance to realize the real-time and on-line monitoring of concentration of the mixture so that we can take preventive measures and prevent the loss from the pollution and protect the safety of surface water resources. However, conventional analytical methods are complicated and time-consuming. The UV-Visible spectroscopy has remarkable superiority over traditional technologies. Not only can it directly or indirectly measure most of the metal ions, organic pollutants, Chemical Oxygen Demand(COD) and other parameters in water, but it also has the advantages of simple structure, small volume, low cost, no secondary pollution, and easy operation, etc. Herein, in this work, we proposed a new quantitative method, which combined ultraviolet (UV) spectrophotometry with partial least squares (PLS) regression (PLS-1 and PLS-2), to quickly determine the content of NaCl, NaOH, and PEA simultaneously from mixed water samples. First of all, the linear concentrations which ranged from 6.03×10^-6 mol/L to 2.04×10^-3 mol/L for NaCl, from 1.94×10^-5 mol/L to 1.32×10^-3 mol/L for NaOH and from 4.03×10^-8 mol/L to 5.15×10^-5 mol/L for PEA solutions were prepared respectively, then the calibration models were constructed by using 49 reference mixed samples in the calibration set and optimized by full cross-validation. In addition, the predictive performance of the optimized models was validated by 21 mixed samples in an independent test set. The root mean square error of prediction (RMSEP) values were lower than 4.60×10^-6 for NaCl, 5.0×10^-6 for NaOH, and 9×10^-8 for PEA in both PLS models. Finally, the optimized PLS-1 and PLS-2 models were successfully applied to simultaneously determine five ternary mixtures of NaCl, NaOH and PEA added into the natural water samples. The average recovery was close to 100% for each of the three components. Thus, UV spectrophotometry combined with PLS regression method can be considered as a promising strategy to conduct the concentration measurements of NaCl, NaOH and PEA in water.