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A low power ultra violet spectrophotometer for measurement of nitrate in seawater: introduction calibration and initial sea trials

A low power ultra violet spectrophotometer for measurement of nitrate in seawater: introduction calibration and initial sea trials
A low power ultra violet spectrophotometer for measurement of nitrate in seawater: introduction calibration and initial sea trials
A low power UV spectroabsorptiometer has been developed to measure the concentration of dissolved nitrate in seawater, in situ, with a rapid 1 Hz response. Measurements at a number of wavelengths in the region of 220 nm determine the concentrations of dissolved nitrate, sea salt and, possibly, dissolved organics, whilst a third channel at 300 nm acts as a reference channel to correct for light intensity changes related to lamp output and scattering by particles in seawater. This paper describes the first prototype UV nitrate sensor designed to evaluate and compare options for the light source, spectral filter and detector. The choice of components was based on a compromise between performance, cost, power consumption and convenience of use. The eventual instrument uses a xenon flashlamp light source, fused silica windows and lenses, a sample cavity, a grating spectrometer and UV enhanced silicon photodiode detectors. The power consumption of the sensor was typically from 3 to 4 W, depending on the selected repetition rate of the flashlamp source. Initial laboratory trials have shown the sensor to be unresponsive to changes in pressure allowing for continuous use to depths of up to 5000 m. Initial responses to changes in temperature have been eliminated by the adjustment of the sensor's power supply and lamp flash rate. Calibration of the sensor has been performed under laboratory conditions and resulted in a second order linear fit (r2 > 0.99, p 0.21 µmol/l N03.
Measurements made in situ were compared to concentrations of nitrate determined in water samples using an AAII type autoanalyser. These demonstrated the capability of the instrument to precisely determine nitrate concentrations in seawater.
0003-2670
167-177
Finch, M.S.
16ce99dd-91f3-4bcb-8bbf-e0ba67001efa
Hydes, D.J.
ac7371d4-c2b9-4926-bb77-ce58480ecff7
Clayson, C.H.
7879f8b0-dc81-4ca3-96a8-7529363bd6db
Weigl, B.
a08dee60-9204-4484-bb53-5928ee3f23e7
Dakin, J.P.
04891b9b-5fb5-4245-879e-9e7361adf904
Gwilliam, P.
b8c6c6b8-5ec5-4fe4-a795-ec1f30ce2791
Finch, M.S.
16ce99dd-91f3-4bcb-8bbf-e0ba67001efa
Hydes, D.J.
ac7371d4-c2b9-4926-bb77-ce58480ecff7
Clayson, C.H.
7879f8b0-dc81-4ca3-96a8-7529363bd6db
Weigl, B.
a08dee60-9204-4484-bb53-5928ee3f23e7
Dakin, J.P.
04891b9b-5fb5-4245-879e-9e7361adf904
Gwilliam, P.
b8c6c6b8-5ec5-4fe4-a795-ec1f30ce2791

Finch, M.S., Hydes, D.J., Clayson, C.H., Weigl, B., Dakin, J.P. and Gwilliam, P. (1998) A low power ultra violet spectrophotometer for measurement of nitrate in seawater: introduction calibration and initial sea trials. Analytica Chimica Acta, 377 (2-3), 167-177. (doi:10.1016/S0003-2670(98)00616-3).

Record type: Article

Abstract

A low power UV spectroabsorptiometer has been developed to measure the concentration of dissolved nitrate in seawater, in situ, with a rapid 1 Hz response. Measurements at a number of wavelengths in the region of 220 nm determine the concentrations of dissolved nitrate, sea salt and, possibly, dissolved organics, whilst a third channel at 300 nm acts as a reference channel to correct for light intensity changes related to lamp output and scattering by particles in seawater. This paper describes the first prototype UV nitrate sensor designed to evaluate and compare options for the light source, spectral filter and detector. The choice of components was based on a compromise between performance, cost, power consumption and convenience of use. The eventual instrument uses a xenon flashlamp light source, fused silica windows and lenses, a sample cavity, a grating spectrometer and UV enhanced silicon photodiode detectors. The power consumption of the sensor was typically from 3 to 4 W, depending on the selected repetition rate of the flashlamp source. Initial laboratory trials have shown the sensor to be unresponsive to changes in pressure allowing for continuous use to depths of up to 5000 m. Initial responses to changes in temperature have been eliminated by the adjustment of the sensor's power supply and lamp flash rate. Calibration of the sensor has been performed under laboratory conditions and resulted in a second order linear fit (r2 > 0.99, p 0.21 µmol/l N03.
Measurements made in situ were compared to concentrations of nitrate determined in water samples using an AAII type autoanalyser. These demonstrated the capability of the instrument to precisely determine nitrate concentrations in seawater.

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Published date: 31 December 1998

Identifiers

Local EPrints ID: 77785
URI: https://eprints.soton.ac.uk/id/eprint/77785
ISSN: 0003-2670
PURE UUID: bd7f58ca-1e0e-450f-926d-f1679831d0cb

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Date deposited: 11 Mar 2010
Last modified: 25 Jul 2018 16:32

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