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Testing an AChE sensor for arsenic analysis with groundwater samples from Shepley’s Hill Landfill
Citation:
Li, T. AND R. Ford. Testing an AChE sensor for arsenic analysis with groundwater samples from Shepley’s Hill Landfill. ACS Fall 2023: Harnessing the Power of Data, San Francisco, CA, August 13 - 17, 2023.
Impact/Purpose:
This presentation reports the evaluation of the prototypic AChE sensor with field-collected samples. The objective is to validate the technology in relevant environment. A framework of Technology Readiness Level has been developed to guide sensor development. The reported activity fits in Level 5. Findings: - The enzyme-based sensor tolerates complex matrices. Carbon screen-printed electrode remains a viable technology platform. - Oxalic acid modification has helped to stabilize speciation, but more study is needed to understand matrix impact. - Current method (pipetting, glutaraldehyde crosslinking) for sensor fabrication is not suitable for TLR-5 and higher-level development due to large errors. - In Red Cove area, As in the north area was mostly As(III), while in the west and south the speciation was mixture of As(V) and As(III). In the south side, low As mobility strongly correlated to low Fe mobility.
Description:
Arsenic discharge and mobilization from the pollution source depend on the minerals that host arsenic, the matrix of local water, the redox condition, and the water flow. A disposable enzyme sensor has been developed for As(III) determination in site assessment. To evaluate the sensor performance in different matrices, it was tested with groundwater samples from Shepley’s Hill Landfill, MA. Shepley’s Hill Landfill is an 84-acre superfund site that discharges about 17 kg of arsenic/year through groundwater. Historical data during 2006 and 2007 showed that the groundwater had significant spatiotemporal variations in both physical conditions and chemical compositions. Arsenic concentration was in the range of 70-1100 mg/L with a median of 960 mg/L. Importantly, most samples were high in Fe (II) (median = 34.6 mg/L), which was oxidized and caused arsenic precipitation in < 20 min when exposed to air. For arsenic preservation, a sample preparation involving modification with oxalic acid was developed. No ferric oxide precipitation took place in oxalic acid solution. In 5 mM oxalic acid arsenic speciation was stable for 15 days. The precision and accuracy of the sensor were evaluated in two batches groundwater samples taken in 2019. The accuracy of the sensor was evaluated by comparing the result with those obtained using ICP-AES. In the range of 5 – 1292 mg/L of As(III), the correlation coefficient was R2 = 0.9503 (n=10). For precision determination, 24 field samples were collected and analyzed. The samples contained 22-741 mg/L total arsenic, 0.06-44 mg/L of iron and 0.11-6.2 mg/L of manganese. The standard deviation for As (III) measured by the sensor was 191 ± 129 mg/L (n = 24).