Ion-Selective Analysis of Water Quality in the contexts of Plant Production, Biological Life Support Systems and Space Exploration
The present work explores the use of ion-selective sensors for nutrient sensing in waters relevant to plant production, biological life support systems (BLSS) and space exploration. Ion-selective detection capabilities are essential in managing environments and life support systems for humans on long-duration space missions. HPLC remains the most effective method for ion-selective analysis of water samples however the technology is large, expensive, relatively difficult to operate and requires consumable materials, making it unfavourable for use in space. Single ion-selective sensors are commercially available such as ion-selective electrodes or ion-selective field effect transistors and prototype technologies are emerging such as ion-selective optrodes. Ion-selective optrodes were selected to develop an online ion-detection system for potassium, calcium, sodium and nitrate, using optrode sensors obtained from collaborators at the Canadian Space Agency and the National Optics Institute. They were chosen based on their small mass, compact design, simple operation, and insensitivity to electric-field interference. During characterization trials, several issues were identified using optrodes in nutrient solutions: material selection of system components is critical as contamination influences optical properties of the sensors; fabrication practices are critical and optrodes mechanically coated in a clean environment perform best; biofouling quickly impairs optrode performance; and light exposure degrades optrode dyes. Based on these results a prototype Ion-Selective Optrode System (ISOS) was developed. The ISOS was tested in the context of robotic-science exploration of Saturn's moon Titan on the remote lake Laguna Negra, Chile. The ISOS successfully detected calcium and sodium ions in surface water samples. Light-plant-nutrient interactions were also studied and the dietary habits ofLactuca sativa cv. New Red Fire were monitored in response to blue (440 nm) and red (660 nm) light environments. Results indicate light quality influences the uptake of certain nutrients. Plants under blue light consumed more nitrogen. The uptake of certain metal ions (Zinc and Iron) also appear favoured by blue or red light treatments repsectively. These results have significant implications for recirculating nutrient systems inherent in BLSS.