Lab-on-Chip Measurement of Nitrate and Nitrite for In Situ Analysis of Natural Waters

Beaton, Alexander D., Cardwell, Christopher L., Thomas, Rupert S., Sieben, Vincent J., Legiret, François-Eric, Waugh, Edward M., Statham, Peter J., Mowlem, Matthew C. and Morgan, Hywel (2012) Lab-on-Chip Measurement of Nitrate and Nitrite for In Situ Analysis of Natural Waters. Environmental Science & Technology, 46 (17), 9548-9556. (doi:10.1021/es300419u).

Abstract

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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Contributors

Author: Matthew C. Mowlem

Author: Hywel Morgan

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