Marine Science Faculty Publications

Seawater pH Measurements: an At-sea Comparison of Spectrophotometric and Potentiometric Methods

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Spectrophotometric procedures utilizing sulfonephthalein indicators provide rapid, quantitative measurements of seawater pH. In a series of shipboard comparison, the average difference between our spectrophotometric and potentiometric pH measurements was 0.012 ± 0.010 + ph (spec., 20°C, free H+ scale) - pH (potent., 25°C, NBS scale). The ±0.010 S.E. obtained in our at-sea comparison suggests that the imprecision associated with either type of measurement was <±0.010. Spectrophotometric procedures involving dissolved sulfonephthalein indicators appear well suited to in situ analysis of both pH and alkalinity.

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Deep Sea Research Part A. Oceanographic Research Papers, v. 35, issue 8, p. 1405-1410