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Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements

Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements
Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements
High quality carbonate chemistry measurements are required in order to fully understand the dynamics of the oceanic carbonate system. Seawater pH data with good spatial and temporal coverage are particularly critical to apprehend ocean acidification phenomena and their consequences. There is a growing need for autonomous in situ instruments that measure pH on remote platforms. Our aim is to develop an accurate and precise autonomous in situ pH sensor for long term deployment on remote platforms. The widely used spectrophotometric pH technique is capable of the required high-quality measurements. We report a key step towards the miniaturization of a colorimetric pH sensor with the successful implementation of a simple microfluidic design with low reagent consumption. The system is particularly adapted to shipboard deployment: high quality data was obtained over a period of more than a month during a shipboard deployment in northwest European shelf waters, and less than 30 mL of indicator was consumed. The system featured a short term precision of 0.001 pH (n = 20) and an accuracy within the range of a certified Tris buffer (0.004 pH). The quality of the pH system measurements have been checked using various approaches: measurements of certified Tris buffer, measurement of certified seawater for DIC and TA, comparison of measured pH against calculated pH from pCO2, DIC and TA during the cruise in northwest European shelf waters. All showed that our measurements were of high quality. The measurements were made close to in situ temperature (+0.2 ?C) in a sampling chamber which had a continuous flow of the ship’s underway seawater supply. The optical set up was robust and relatively small due to the use of an USB mini-spectrometer, a custom made polymeric flow cell and an LED light source. The use of a three wavelength LED with detection that integrated power across the whole of each LED output spectrum indicated that low wavelength resolution detectors can be used instead of the current USB mini spectrophotometer. Artefacts due to the polychromatic light source and inhomogeneity in the absorption cell are shown to have a negligible impact on the data quality. The next step in the miniaturization of the sensor will be the incorporation of a photodiode as detector to replace the spectrophotometer.
pH, colorimetry, sensor development, microfluidic pH sensor, LED, autonomous
0003-2670
124-131
Rérolle, Victoire M.C.
454aa1fc-b776-4df7-a763-721155a7be40
Floquet, Cedric F.A.
9e0adc5e-10f1-4d67-81cc-63157949b704
Harris, Andy J.K.
4986460f-0731-4c65-9a10-ac8ac1624e89
Mowlem, Matt C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Bellerby, Richard R.G.J.
ce2ed8d6-fe0c-443f-af66-a7db52c02838
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9
Rérolle, Victoire M.C.
454aa1fc-b776-4df7-a763-721155a7be40
Floquet, Cedric F.A.
9e0adc5e-10f1-4d67-81cc-63157949b704
Harris, Andy J.K.
4986460f-0731-4c65-9a10-ac8ac1624e89
Mowlem, Matt C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Bellerby, Richard R.G.J.
ce2ed8d6-fe0c-443f-af66-a7db52c02838
Achterberg, Eric P.
685ce961-8c45-4503-9f03-50f6561202b9

Rérolle, Victoire M.C., Floquet, Cedric F.A., Harris, Andy J.K., Mowlem, Matt C., Bellerby, Richard R.G.J. and Achterberg, Eric P. (2013) Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements. Analytica Chimica Acta, 786, 124-131. (doi:10.1016/j.aca.2013.05.008).

Record type: Article

Abstract

High quality carbonate chemistry measurements are required in order to fully understand the dynamics of the oceanic carbonate system. Seawater pH data with good spatial and temporal coverage are particularly critical to apprehend ocean acidification phenomena and their consequences. There is a growing need for autonomous in situ instruments that measure pH on remote platforms. Our aim is to develop an accurate and precise autonomous in situ pH sensor for long term deployment on remote platforms. The widely used spectrophotometric pH technique is capable of the required high-quality measurements. We report a key step towards the miniaturization of a colorimetric pH sensor with the successful implementation of a simple microfluidic design with low reagent consumption. The system is particularly adapted to shipboard deployment: high quality data was obtained over a period of more than a month during a shipboard deployment in northwest European shelf waters, and less than 30 mL of indicator was consumed. The system featured a short term precision of 0.001 pH (n = 20) and an accuracy within the range of a certified Tris buffer (0.004 pH). The quality of the pH system measurements have been checked using various approaches: measurements of certified Tris buffer, measurement of certified seawater for DIC and TA, comparison of measured pH against calculated pH from pCO2, DIC and TA during the cruise in northwest European shelf waters. All showed that our measurements were of high quality. The measurements were made close to in situ temperature (+0.2 ?C) in a sampling chamber which had a continuous flow of the ship’s underway seawater supply. The optical set up was robust and relatively small due to the use of an USB mini-spectrometer, a custom made polymeric flow cell and an LED light source. The use of a three wavelength LED with detection that integrated power across the whole of each LED output spectrum indicated that low wavelength resolution detectors can be used instead of the current USB mini spectrophotometer. Artefacts due to the polychromatic light source and inhomogeneity in the absorption cell are shown to have a negligible impact on the data quality. The next step in the miniaturization of the sensor will be the incorporation of a photodiode as detector to replace the spectrophotometer.

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More information

Published date: 5 July 2013
Keywords: pH, colorimetry, sensor development, microfluidic pH sensor, LED, autonomous
Organisations: Ocean Biochemistry & Ecosystems, Ocean Technology and Engineering

Identifiers

Local EPrints ID: 354024
URI: http://eprints.soton.ac.uk/id/eprint/354024
ISSN: 0003-2670
PURE UUID: db18ca59-a603-4376-a3b3-c4752d8d94cc
ORCID for Matt C. Mowlem: ORCID iD orcid.org/0000-0001-7613-6121

Catalogue record

Date deposited: 28 Jun 2013 09:19
Last modified: 15 Mar 2024 03:02

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Contributors

Author: Victoire M.C. Rérolle
Author: Cedric F.A. Floquet
Author: Andy J.K. Harris
Author: Matt C. Mowlem ORCID iD
Author: Richard R.G.J. Bellerby

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