Water quality assessment using a portable UV optical absorbance nitrate sensor with a scintillator and smartphone camera

Abstract

Nitrate contamination of water sources is a global environmental concern. A major source of pollution is agricultural runoff, which can contain decomposed organic matter, fertilizer, and animal or human waste. Nitrate adversely affects the stability of water systems such as dams and rivers and thus also public health. Regulation is essential but difficult to implement, given that measuring nitrates is laborious, and normally done using chemical assays in laboratories. We present a novel portable nitrate sensor that uses a smartphone camera fitted with low-cost optics. The sensor uses ultraviolet absorbance analysis to detect nitrates in water samples and quantify the concentration. The sensor’s absorptivity when a bandpass filter was used was 0.0681 L∙mg⁻¹∙cm⁻¹ compared to 0.0934 L∙mg⁻¹∙cm⁻¹ measured with a spectrophotometer in a laboratory. Measurements by the sensor of the concentration of nitrates in two environmental samples differed from those taken by the spectrophotometer by 19% and 7%. The sensor achieved a nitrate concentration measurement resolution of 0.2 mg∙L⁻¹, and a detection range of 0–5 mg∙L⁻¹, with higher concentrations requiring dilution to quantify. Our tests showed that the smartphone-based nitrate sensor is sufficiently accurate to be used as an inexpensive instrument for nitrate analysis in the field.