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Methodology

The system is based on the principle of colorimetric determination of a sulfonephthalein pH indicator (purified m-cresol purple, purchased from the Byrne Lab at USF), which demonstrates high precision (±0.0004) and accuracy (~±0.002) compared to other methods. Indicator dye is added to seawater samples in a temperature controlled 10cm cell within the spectrophotometer. Dye absorbance ratios are corrected for perturbation effects and pH is calculated using the Liu et al. (2011) parameterization for m-cresol purple.

Reference

Dickson, A.G. Sabine, C.L. and Christian, J.R. (Eds.) 2007. Guide to Best Practices for Ocean CO2 Measurements. PICES Special Publication 3, 191 pp.

Carter, B. R., J. A. Radich, H. L. Doyle, and A. G. Dickson. 2013. An automated system for spectrophotometric seawater pH measurements. Limnology and Oceanography: Methods 11: 16–27. doi:10.4319/lom.2013.11.16

Liu, X., M. C. Patsavas, and R. H. Byrne. 2011. Purification and characterization of meta-cresol purple for spectrophotometric seawater ph measurements. Environmental Science and Technology 45: 4862–4868. doi:10.1021/es200665d