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Spectrophotometric High-precision Seawater Ph Determination for Use in Underway Measuring Systems : Volume 7, Issue 5 (04/10/2011)

By Aßmann, S.

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Book Id: WPLBN0004020531
Format Type: PDF Article :
File Size: Pages 11
Reproduction Date: 2015

Title: Spectrophotometric High-precision Seawater Ph Determination for Use in Underway Measuring Systems : Volume 7, Issue 5 (04/10/2011)  
Author: Aßmann, S.
Volume: Vol. 7, Issue 5
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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Körtzinger, A., Frank, C., & Aßmann, S. (2011). Spectrophotometric High-precision Seawater Ph Determination for Use in Underway Measuring Systems : Volume 7, Issue 5 (04/10/2011). Retrieved from

Description: Helmholtz-Zentrum Geesthacht, Institute of Coastal Research, Max-Planck-Str. 1, 21502 Geesthacht, Germany. Autonomous sensors are required for a comprehensive documentation of the changes in the marine carbon system and thus to differentiate between its natural variability and anthropogenic impacts. Spectrophotometric determination of pH – a key variable of the seawater carbon system – is particularly suited to achieve precise and drift-free measurements. However, available spectrophotometric instruments are not suitable for integration into automated measurement systems (e.g. FerryBox) since they do not meet the major requirements of reliability, stability, robustness and moderate cost. Here we report on the development and testing of a~new indicator-based pH sensor that meets all of these requirements. This sensor can withstand the rough conditions during long-term deployments on ships of opportunity and is applicable to the open ocean as well as to coastal waters with a complex matrix and highly variable conditions. The sensor uses a high resolution CCD spectrometer as detector connected via optical fibers to a custom-made cuvette designed to reduce the impact of air bubbles. The sample temperature can be precisely adjusted (25 °C ± 0.006 °C) using computer-controlled power supplies and Peltier elements thus avoiding the widely used water bath. The overall setup achieves a measurement frequency of 1 min−1 with a precision of ±0.0007 pH units, an average offset of +0.0005 pH units to a reference system, and an offset of +0.0081 pH units to a certified standard buffer. Application of this sensor allows monitoring of seawater pH in autonomous underway systems, providing a key variable for characterization and understanding of the marine carbon system.

Spectrophotometric high-precision seawater pH determination for use in underway measuring systems

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