An autonomous freshwater pH sensor: development and applications

所提议活动的智力价值。pH值是淡水系统中常用的测量参数。在许多情况下需要连续的pH测量，但目前的技术无法提供高质量、长期、无操作的测量。我们建议严格评估一种新型分光光度pH传感器，它提供了无漂移淡水pH测量的潜力。该设计直接来源于潜水式自主系泊二氧化碳传感器（SAMI-CO2）（DeGrandpre et al. 1995,1999）。SAMI-pH传感器采用与SAMI-CO2相同的设计。通过Sunburst Sensors （www.sunburstsensors.com）提供SAMI技术将极大地促进SAMI- ph的开发、测试和未来商业化。人们普遍认为分光光度pH法不适用于分析弱缓冲水，如淡水，因为指示剂会改变样品的pH值。SAMI-pH设计采用了一种简单的方法来量化无扰动ph值。该资助的目标是：1)在实验室中使用一系列弱缓冲样品严格测试设计，2)通过一系列温度和离子强度量化指标平衡常数，以及3)在具有广泛碱度，腐殖质含量和颗粒负载的自然水中严格测试传感器性能。现场研究的SAMI-pH数据将与现场pH电极测量值和从二氧化碳分压和碱度计算的pH值进行比较。将评估长期（数周到数月）的pH值准确性、精度和动态范围，并根据这些结果进行设计更改。受地雷影响的溪流的实地研究将利用两个SAMI-pH传感器来量化纵向梯度和pH变化率（以前使用电位电极非常困难）。pH值数据将用于模拟地球化学平衡，以预测金属负载。组合模型将使金属变异性和载荷归因于特定的流内过程。拟议活动的更广泛影响。有三个广泛的影响：1)在化学传感器开发领域受过培训的学生将随后成为这一重要研究领域的下一代领导者；2)提高对水生生态系统生物地球化学循环的认识将有助于更好地预测人为影响，从而更好地管理我们的自然资源；3)自主化学传感技术的进步将有利于环境、工业和国家安全，使远程和持续监测环境中的化学物种成为可能。

DeGramdpre0337460Intellectual merit of the proposed activity. pH is a commonly measured parameter in freshwater systems. Continuous pH measurements are desired in many situations, yet present day technology is incapable of providing good quality, long-term, operator-free measurements. We propose to rigorously evaluate a novel spectrophotometric pH sensor that offers the potential for drift-free freshwater pH measurements. The design derives directly from the Submersible Autonomous Moored Sensor for CO2 (SAMI-CO2)(DeGrandpre et al. 1995, 1999). The SAMI-pH sensor utilizes the same design as SAMI-CO2. The availability of the SAMI technology through Sunburst Sensors (www.sunburstsensors.com) will greatly facilitate development, testing and future commercialization of SAMI-pH. Spectrophotometric pH methods are widely thought to be inadequate for analysis of weakly buffered waters such as freshwater because the indicator alters the pH of the sample. The SAMI-pH design utilizes a straightforward methodology to quantify the perturbation-free pH. The objectives of this grant are to 1) rigorously test the design in the laboratory using a series of weakly buffered samples, 2) quantify indicator equilibrium constants through a range of temperature and ionic strength, and 3) rigorously test the sensor performance in natural waters with a wide range of alkalinities, humic content, and particle loading. SAMI-pH data from the field studies will be compared to in situ pH electrode measurements and pH computed from pCO2 and alkalinity. Long-term (weeks to months) pH accuracy, precision and dynamic range will be assessed and design changes will be made based on these results. Field studies of mine-impacted streams will utilize two SAMI-pH sensors to quantify longitudinal gradients and pH rates of change (previously very difficult using potentiometric electrodes). The pH data will be used to model geochemical equilibria to predict metal loading. The combined models will enable metal variability and loading to be attributed to specific in-stream processes.Broader impact of the proposed activity . There are three broad impacts: 1) students trained in the area of chemical sensor development will subsequently become the next generation of leaders in this important research area; 2) an improved understanding of biogeochemical cycling in aquatic ecosystems will allow better prediction of anthropogenic impacts and hence management of our natural resources; and 3) advancements in autonomous chemical sensing technology will benefit the environment, industry and national security by making it possible to remotely and continuously monitor chemical species in the environment.