Evaluation of Low-Cost UV-Vis Spectroscopy for Measuring Nitrate Using Synthetic Water Samples

Highlights A novel low-cost, modular spectroscopy system is compared to a standard system using synthetic samples, principal component analysis, and partial least squares regression. The information contained in the data produced by the two systems is similar according to principal component analysis. The low-cost system was able to accurately predict nitrate concentrations in concentrated and diluted samples using partial least squares regression. The methodology could be applied to water quality analysis in agriculture and water resources management. Abstract. Water quality data collection is an essential component of water systems management. For instance, the effective management of nutrients in hydroponic systems is necessary for maximizing yields efficiently and sustainably. Additionally, nutrients in natural and engineered waterbodies must be monitored to ensure they are meeting the required chemical characteristics for their ecological and social functions. However, conventional water quality data collection methods place limitations on water systems management due to their high resource requirements. Nitrate (NO3) is a major nutrient in ecological and agricultural systems, which can be reliably measured with ultraviolet-visible (UV-Vis) spectroscopy, a highly established technique for water quality analysis. The goal of this research was to evaluate a novel, low-cost, modular UV-Vis spectroscopy setup (GatorSpec) for the measurement of NO3 concentration in chemically complex solutions. UV-Vis absorbance of synthetic samples was measured using the GatorSpec and a commonly used bench-top laboratory spectroscopy system, the NanoDrop2000C. These data were analyzed using principal component analysis (PCA) to compare the spectral data produced by each system and partial least squares (PLS) regression to compare their ability to predict NO3 concentration. Results showed that data from both measurement systems were similar, indicating that the low-cost GatorSpec provided similar measurement accuracy to that of the laboratory reference system, the NanoDrop2000C. The PLS results revealed that for the diluted samples, the models derived from both systems were very good at predicting NO3 concentration. With these outcomes, it can be concluded that the GatorSpec is effective at measuring NO3 concentration in complex solutions and is comparable in performance to that of the NanoDrop2000C. In the future, this low-cost setup could be used to manage NO3 concentrations more efficiently in various applications such as hydroponic plant production, environmental monitoring, and stormwater treatment, which, in turn, could reduce the economic and environmental costs of these systems. Keywords: Low-cost, Synthetic samples, Ultraviolet-visible absorption spectroscopy, Water quality.