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United States Department of Agriculture

Agricultural Research Service

Title: Laboratory Evaluation of Ion-Selective Electrodes for Simultaneous Analysis of Macronutrients in Hydroponic Solution

item Kim, Hak-jin
item Son, Dong-wook
item Kim, Young-joo
item Park, Doo-san
item Sudduth, Kenneth - Ken

Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2010
Publication Date: 7/18/2010
Citation: Kim, H.J., Son, D.W., Kim, Y., Park, D.S., Sudduth, K.A. 2010. Laboratory Evaluation of Ion-Selective Electrodes for Simultaneous Analysis of Macronutrients in Hydroponic Solution. In: Proceedings of the 10th International Conference on Precision Agriculture, July 18-21, 2010, Denver, Colorado. 2010 CDROM.

Interpretive Summary: The conventional practice of laboratory nutrient analysis is costly and time consuming when applied at the intensity needed to monitor and control solutions used for hydroponic crop production. A more efficient approach would be to sense nutrient status in the hydroponic solution in real time. One candidate for real-time sensing is ion-selective electrodes (ISE) technology. The goal of this research was to evaluate the accuracy of selected ISEs for measuring nitrate, phosphate, potassium, calcium, and magnesium in hydroponic solutions. The selected ISEs were able to quantify nitrate, phosphate, potassium, and calcium at levels typically used in production of paprika, a major hydroponic crop in Korea. However, magnesium measurements were not successful because the magnesium ISE was sensitive to the presence of calcium in the solution. This research is a first step toward a viable real-time nutrient monitoring and control system for hydroponic production. Such a system could provide lower food production costs and reduced environmental impacts, benefiting both producers and consumers.

Technical Abstract: Automated sensing of macronutrients in hydroponic solution would allow more efficient management of nutrients for crop growth in closed hydroponic systems. Ion-selective microelectrode technology requires an ion-selective membrane or a solid metal material that responds selectively to one analyte in the presence of other ions in a solution. This study reports on the evaluation of a sensor array consisting of five different ion selective electrodes (ISEs) for simultaneous determination of nitrate (NO3-N), orthophosphate (H2PO4-), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) ions in hydroponic solution. Ion-selective membranes for nitrate, potassium, calcium, and magnesium and a cobalt-rod metal for phosphate were evaluated using an automated test stand by comparing the sensing elements with respect to their sensitivity and selectivity in standard solutions. The feasibility of using the sensor array for simultaneous determination of the five ions over the typical range of macronutrient concentrations in hydroponic solutions was examined. The sensitivity and selectivity of PVC membrane-based ion-selective electrodes with TDDA-NPOE, valinomycin, and calcium ionophore II for NO3-, K+ and Ca2+ respectively, and of a cobalt rod-based ion-selective electrode for H2PO4- were satisfactory for measuring macronutrients over typical ranges of hydroponic concentrations. However, the use of potassium hydrogen phthalate (KHP) buffer solution was needed to measure phosphorus ions with acceptable sensitivity. Further studies to identify a magnesium ion-selective membrane that shows a sensitive response to magnesium in the presence of calcium are needed.

Last Modified: 06/28/2017
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