Title :

Characterisation and deployment of an immobilised pH sensor spot towards surface ocean pH measurements

Author(s) :

Clarke, Jennifer S. [Auteur correspondant]
National Oceanography Centre [Southampton] [NOC]
Achterberg, Eric P. [Auteur]
Austral, Boréal et Carbone [ABC]
National Oceanography Centre [Southampton] [NOC]
Helmholtz Centre for Ocean Research [Kiel] [GEOMAR]
Rérolle, Victoire [Auteur]
Austral, Boréal et Carbone [ABC]
Abi Kaed Bey, Samer [Auteur]
National Oceanography Centre [Southampton] [NOC]
American University of Science and Technology [AUST]
Floquet, Cedric F.A. [Auteur]
National Oceanography Centre [Southampton] [NOC]
Mowlem, Matthew C. [Auteur]
National Oceanography Centre [Southampton] [NOC]

Journal title :

Analytica Chimica Acta

Pages :

69-80

Publisher :

Elsevier Masson

Publication date :

2015-10

ISSN :

0003-2670

HAL domain(s) :

Planète et Univers [physics]/Sciences de la Terre/Océanographie
Physique [physics]/Physique [physics]/Géophysique [physics.geo-ph]

English abstract : [en]

The oceans are a major sink for anthropogenic atmospheric carbon dioxide, and the uptake causes changes to the marine carbonate system and has wide ranging effects on flora and fauna. It is crucial to develop analytical ...
Show more >The oceans are a major sink for anthropogenic atmospheric carbon dioxide, and the uptake causes changes to the marine carbonate system and has wide ranging effects on flora and fauna. It is crucial to develop analytical systems that allow us to follow the increase in oceanic pCO₂ and corresponding reduction in pH. Miniaturised sensor systems using immobilised fluorescence indicator spots are attractive for this purpose because of their simple design and low power requirements. The technology is increasingly used for oceanic dissolved oxygen measurements. We present a detailed method on the use of immobilised fluorescence indicator spots to determine pH in ocean waters across the pH range 7.6–8.2. We characterised temperature (−0.046 pH/°C from 5 to 25 °C) and salinity dependences (−0.01 pH/psu over 5–35), and performed a preliminary investigation into the influence of chlorophyll on the pH measurement. The apparent pKa of the sensor spots was 6.93 at 20 °C. A drift of 0.00014 R (ca. 0.0004 pH, at 25 °C, salinity 35) was observed over a 3 day period in a laboratory based drift experiment. We achieved a precision of 0.0074 pH units, and observed a drift of 0.06 pH units during a test deployment of 5 week duration in the Southern Ocean as an underway surface ocean sensor, which was corrected for using certified reference materials. The temperature and salinity dependences were accounted for with the algorithm, R=0.00034−0.17·pH+0.15·S2+0.0067·T−0.0084·S·1.075R=0.00034−0.17·pH+0.15·S2+0.0067·T−0.0084·S·1.075. This study provides a first step towards a pH optode system suitable for autonomous deployment. The use of a short duration low power illumination (LED current 0.2 mA, 5 μs illumination time) improved the lifetime and precision of the spot. Further improvements to the pH indicator spot operations include regular application of certified reference materials for drift correction and cross-calibration against a spectrophotometric pH system. Desirable future developments should involve novel fluorescence spots with improved response time and apparent pKa values closer to the pH of surface ocean waters.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

Collections :

• Centre de Recherche en Informatique, Signal et Automatique de Lille (CRIStAL) - UMR 9189

Source :

Harvested from HAL