Journal of Biosystems Engineering

Korean Society for Agricultural Machinery (한국농업기계학회)
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An Automated Water Nitrate Monitoring System based on Ion-Selective Electrodes

  • Cho, Woo Jae (Dept. of Biosystems and Biomaterials Engineering, College of Agriculture and Life Sciences, Seoul National University) ;
  • Kim, Dong-Wook (Dept. of Biosystems and Biomaterials Engineering, College of Agriculture and Life Sciences, Seoul National University) ;
  • Jung, Dae Hyun (Dept. of Biosystems and Biomaterials Engineering, College of Agriculture and Life Sciences, Seoul National University) ;
  • Cho, Sang Sun (Scientec Lab Center co., LTD) ;
  • Kim, Hak-Jin (Dept. of Biosystems and Biomaterials Engineering, College of Agriculture and Life Sciences, Seoul National University)
  • Received : 2016.04.06
  • Accepted : 2016.05.27
  • Published : 2016.06.01
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Abstract

Purpose: In-situ water quality monitoring based on ion-selective electrodes (ISEs) is a promising technique because ISEs can be used directly in the medium to be tested, have a compact size, and are inexpensive. However, signal drift can be a major concern with on-line management systems because continuous immersion of the ISEs in water causes electrode degradation, affecting the stability, repeatability, and selectivity over time. In this study, a computer-based nitrate monitoring system including automatic electrode rinsing and calibration was developed to measure the nitrate concentration in water samples in real-time. Methods: The capabilities of two different types of poly(vinyl chloride) membrane-based ISEs, an electrode with a liquid filling and a carbon paste-based solid state electrode, were used in the monitoring system and evaluated on their sensitivities, selectivities, and durabilities. A feasibility test for the continuous detection of nitrate ions in water using the developed system was conducted using water samples obtained from various water sources. Results: Both prepared ISEs were capable of detecting low concentrations of nitrate in solution, i.e., 0.7 mg/L $NO_3-N$. Furthermore, the electrodes have the same order of selectivity for nitrate: $NO_3{^-}{\gg}HCO_3{^-}$ > $Cl^-$ > $H_2PO_4{^-}$ > $SO{_4}^{2-}$, and maintain their sensitivity by > 40 mV/decade over a period of 90 days. Conclusions: The use of an automated ISE-based nitrate measurement system that includes automatic electrode rinsing and two-point normalization proved to be feasible in measuring $NO_3-N$ in water samples obtained from different water sources. A one-to-one relationship between the levels of $NO_3-N$ measured with the ISEs and standard analytical instruments was obtained.

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