Lab-on-Chip Measurement of Nitrate and Nitrite for In Situ Analysis of Natural Waters
2012
Beaton, Alexander D. | Cardwell, Christopher L. | Thomas, Rupert S. | Sieben, Vincent J. | Legiret, François-Eric | Waugh, Edward M. | Statham, Peter J. | Mowlem, Matthew C. | Morgan, Hywel
Microfluidic technology permits the miniaturization of chemical analytical methods that are traditionally undertaken using benchtop equipment in the laboratory environment. When applied to environmental monitoring, these “lab-on-chip” systems could allow high-performance chemical analysis methods to be performed in situ over distributed sensor networks with large numbers of measurement nodes. Here we present the first of a new generation of microfluidic chemical analysis systems with sufficient analytical performance and robustness for deployment in natural waters. The system detects nitrate and nitrite (up to 350 μM, 21.7 mg/L as NO₃–) with a limit of detection (LOD) of 0.025 μM for nitrate (0.0016 mg/L as NO₃–) and 0.02 μM for nitrite (0.00092 mg/L as NO₂–). This performance is suitable for almost all natural waters (apart from the oligotrophic open ocean), and the device was deployed in an estuarine environment (Southampton Water) to monitor nitrate+nitrite concentrations in waters of varying salinity. The system was able to track changes in the nitrate–salinity relationship of estuarine waters due to increased river flow after a period of high rainfall. Laboratory characterization and deployment data are presented, demonstrating the ability of the system to acquire data with high temporal resolution.
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