Spectrophotometric seawater pH measurements: total hydrogen ion concentration scale calibration of m-cresol purple and at-sea results

Spectrophotometric open-ocean seawater pH measurements are simple, fast and precise. The sulfonephthalein indicator m-cresol purple (mCP) is recommended for open-ocean surface-to-deep pH measurements. The salinity- and temperature-dependence of such measurements (293⩽T⩽303 and 30⩽S⩽37) is given as: pHT(sw) = 1245.69T + (2.11 × 10−3)(35 − S) + log(R − 0.00692.2220 − R0.1330) on the total hydrogen ion concentration scale ([H+]T = [H+]f + [HSO4−]), in units of mol·(kg-soln)−1. R is the ratio of indicator absorbances at molar absorptivity maxima (i.e. R + 578A/434A). The at-sea analytical precision of the technique, evaluated on two recent NOAA cruises, is approximately 0.0004 pH units.

[1]  R. Feely,et al.  The internal consistency of CO2 measurements in the equatorial Pacific , 1993 .

[2]  Andrew G. Dickson,et al.  The estimation of acid dissociation constants in seawater media from potentionmetric titrations with strong base. I. The ionic product of water — Kw , 1979 .

[3]  R. Byrne,et al.  Spectrophotometric procedures for determination of sea water alkalinity using bromocresol green , 1993 .

[4]  K. H. Khoo,et al.  Determination of hydrogen ion concentrations in seawater from 5 to 40.degree.C: standard potentials at salinities from 20 to 45% , 1977 .

[5]  A. Dickson.  pH buffers for sea water media based on the total hydrogen ion concentration scale , 1993 .

[6]  Robert H. Byrne,et al.  High precision multiwavelength pH determinations in seawater using cresol red , 1989 .

[7]  Ching-ling Wei.  Carbonate chemistry of the North Pacific Ocean , 1985 .

[8]  A. Dickson.  pH scales and proton-transfer reactions in saline media such as sea water , 1984 .

[9]  J. P. Riley,et al.  The effect of analytical error on the evaluation of the components of the aquatic carbon-dioxide system , 1978 .

[10]  C. Baes,et al.  The hydrolysis of cations , 1986 .

[11]  Robert H. Byrne,et al.  Seawater pH measurements: an at-sea comparison of spectrophotometric and potentiometric methods , 1988 .

[12]  A. Dickson.  Standard potential of the reaction: , and and the standard acidity constant of the ion HSO4− in synthetic sea water from 273.15 to 318.15 K , 1990 .

[13]  Ingemar Hansson.  A new set of pH-scales and standard buffers for sea water , 1973 .

[14]  C.T.A. Chen,et al.  Carbonate chemistry of the Bering Sea , 1985 .

[15]  D. King,et al.  Determination of seawater pH from 1.5 to 8.5 using colorimetric indicators , 1989 .

[16]  Robert H. Byrne,et al.  Standardization of standard buffers by visible spectrometry , 1987 .

[17]  George L. Pickard,et al.  Descriptive Physical Oceanography: An Introduction , 1963 .

[18]  Robert H. Byrne,et al.  Spectrophotometric determination of seawater pH using phenol red , 1985 .

[19]  F. Millero,et al.  A comparison of the equilibrium constants for the dissociation of carbonic acid in seawater media , 1987 .