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Development of a Disposable AChE Sensor for As(III) and Field Analysis Method; Tests with Groundwater Samples from Shepley’s Hill Landfill
Citation:
Li, T., R. Ford, J. Berberich, E. Sahle-Demessie, E. Varughese, AND Rick Wilkin. Development of a Disposable AChE Sensor for As(III) and Field Analysis Method; Tests with Groundwater Samples from Shepley’s Hill Landfill. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-21/032, 2021.
Impact/Purpose:
The objectives of this interim report are to summarize the findings in the development of a disposable sensor for in-situ arsenic determination, highlight the achievements and issues identified, and propose the path forward.
Description:
The work is planned in three stages. The first stage is for sensor prototype design involving survey and selection of the bioreceptor and a transduction mechanism, and the development of a prototypic sensor. In the second stage, the lab prototype is put to test with samples from field to identify gaps for practical use. The prototype is redesigned in this stage to give the ¿-prototype, in which all necessary features for a product are embedded. Product development is in the third stage. Each stage has multiple tasks. They are created to organize research activity, justify resource requirement, and bench mark the progress. The specific aims are either created by projected needs or based on the proposals to address the issues identified in development. The tasks are interrelated. Their priorities change as the research proceeds. This report covers the activity in Stage 2. Based on the finding, three tasks have been identified in the critical path for prototype design. Key Findings - The sensor can be prepared at the rate of 100 per batch by one person (4 days/batch). The activity of the sensor was 18.8-24.8 uA, with mean = 21.3 ± 1.6 uA (N = 39). The sensor can be dry stored for > 7 days or wet stored in 0.1M Tris-HCl, pH 7.0 for > 150 days. Variation in activity has minimal impact on its sensitivity to 7.5 ¿M As(III). This prototypic sensor is ready for field sample test. - Cluster analysis has been used to review the historical data of RSK wells at Red Cove Area, Shepley’s Hill. Temporal and spatial variation were found in the physical condition and water chemistry. Significant water chemistry change was found in samples of 11-day apart. Water chemistry change is observed within two well groups, suggesting significant spatial variations in < 50 meters. - In the test of May 2019, the accuracy of the sensor was evaluated by comparing the results with that of ICP-AES. In the range of 0 – 20 uM As(III), the correlation was 95%, indicating a good agreement of the two methods. However, the sensor had low precision at low concentrations (< 5 ¿M). - Sample stability has been identified to be a critical issue. The ground water was anoxic and rich in Fe. Exposure to air caused As loss to the precipitate of iron oxide. A new task was created to evaluate sample preservation with oxalic acid. - In the test of October 2019, the sensor was tested with 24 groundwater samples from 12 wells. The objectives include evaluation of sensor precision in wider range of matrices and testing a hypothesis to preserve sample speciation with oxalic acid. We found the sensor had acceptable precision (RSD 13 – 54%) when [As(III)] was between 5- 10 ¿M, and poor precision (RSD 97 – 280%) when [As(III)] was between 0 – 3.4 uM. - Statistical analysis showed that oxalic acid modification prevented Fe precipitation and slowed down the loss of As(III) in sampling. Additional Tasks Planned in Stage 2: - Evaluate oxalic acid modification preserve arsenic speciation in groundwater - Develop pre-reduction of As(V) to As(III) for total arsenic determination. - Survey new enzyme immobilization method for sensor fabrication