Spectrophotometric Seawater pH Measurements: Total Hydrogen Ion Concentration Scale Calibration of emm/em-cresol Purple and At-sea Results

Tonya D. Clayton, Robert H. Byrne

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Abstract

<p> Spectrophotometric open-ocean seawater pH measurements are simple, fast and precise. The sulfonephthalein indicator <em> m </em> -cresol purple ( <em> m </em> CP) is recommended for open-ocean surface-to-deep pH measurements. The salinity- and temperature-dependence of such measurements (293&les; <em> T </em> &les;303 and 30&les; <em> S </em> &les;37) is given as: pHT(sw) =1245.69T+ (2.11 &times; 10&minus;3)(35 &minus; S) + log(R &minus; 0.00692.2220&minus; R0.1330)"&gt;pHT(sw) =1245.69T+ (2.11 &times; 10&minus;3)(35 &minus; S) + log(R &minus; 0.00692.2220&minus; R0.1330) on the total hydrogen ion concentration scale ([H <sup> + </sup> ] <sub> T </sub> = [H <sup> + </sup> ] <sub> f </sub> + [HSO <sub> 4 </sub> <sup> &minus; </sup> ]), in units of mol&middot;(kg-soln) <sup> &minus;1 </sup> . <em> R </em> is the ratio of indicator absorbances at molar absorptivity maxima (i.e. <em> R </em> + <sub> 578 </sub> <em> A </em> / <sub> 434 </sub> <em> A </em> ). The at-sea analytical precision of the technique, evaluated on two recent NOAA cruises, is approximately 0.0004 pH units.</p>
Original languageAmerican English
JournalDeep Sea Research Part I: Oceanographic Research Papers
Volume40
DOIs
StatePublished - Jan 1 1993

Disciplines

  • Life Sciences

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