title: Lab-on-chip measurement of nitrate and nitrite for in situ analysis of natural waters.
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 NO(3)(-)) with a limit of detection (LOD) of 0.025 μM for nitrate (0.0016 mg/L as NO(3)(-)) and 0.02 μM for nitrite (0.00092 mg/L as NO(2)(-)). 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.
authors: National Oceanography Centre, Southampton, United Kingdom. a.beaton@noc.ac.uk
authors: Alexander D
authors: AD
authors: Beaton
authors: Christopher L
authors: CL
authors: Cardwell
authors: Rupert S
authors: RS
authors: Thomas
authors: Vincent J
authors: VJ
authors: Sieben
authors: François-Eric
authors: FE
authors: Legiret
authors: Edward M
authors: EM
authors: Waugh
authors: Peter J
authors: PJ
authors: Statham
authors: Matthew C
authors: MC
authors: Mowlem
authors: Hywel
authors: H
authors: Morgan
mesh_terms: D004784:Environmental Monitoring / Q000295:instrumentation*; D004867:Equipment Design; D056656:Lab-On-A-Chip Devices; D057230:Limit of Detection; D009566:Nitrates / Q000032:analysis*; D009573:Nitrites / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D009573:Nitrites; D014874:Water Pollutants, Chemical