Document Detail

Development of a reference solution for the pH of seawater.
MedLine Citation:
PMID:  17619179     Owner:  NLM     Status:  MEDLINE    
A method that uses a Harned cell to perform potentiometric pH measurements has been optimized and applied to an aqueous solution of simulated seawater that contains sodium perchlorate, sodium sulfate, sodium hydrogen carbonate and boric acid and has an ionic strength I of 0.57 mol kg(-1). The standard metrological approach developed for the measurement of pH in low ionic strength aqueous solutions was maintained, but a few modifications were necessary, and measurement procedures and calculations were modified ad hoc from those adopted in conventional protocols. When determining the standard potential of the cell, E degrees , NaClO4 salt was added to a 0.01 mol/kg HCl solution to attain the same ionic strength as the test solution and to investigate possible specific effects related to the high levels and the nature of the background electrolyte. An appropriate value of gamma (+/-HCl) (0.737) was then selected from the literature, based on a realistic value for I. Finally, in order to convert the acidity function at zero chloride molality into pH, a suitable value of gamma (Cl) (0.929) was calculated. As a result, we obtained pH=8.18 (T=25 degrees C) with an associated expanded uncertainty U=0.01 (coverage factor k=2). The aim was to establish a sound basis for the pH measurement of seawater by identifying the critical points of the experimental and theoretical procedure, and to discuss further possible developments that would be useful for achieving a reference solution.
Enrico Prenesti; Enzo Ferrara; Silvia Berto; Paola Fisicaro; Pier Giuseppe Daniele
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Publication Detail:
Type:  Journal Article     Date:  2007-07-07
Journal Detail:
Title:  Analytical and bioanalytical chemistry     Volume:  388     ISSN:  1618-2642     ISO Abbreviation:  Anal Bioanal Chem     Publication Date:  2007 Aug 
Date Detail:
Created Date:  2007-08-02     Completed Date:  2007-10-03     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101134327     Medline TA:  Anal Bioanal Chem     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  1877-83     Citation Subset:  IM    
Dipartimento di Chimica Analitica dell'Università, via Pietro Giuria 5, 10125, Torino, Italy.
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MeSH Terms
Hydrogen-Ion Concentration*
Osmolar Concentration*
Potentiometry / methods*,  standards
Reference Standards
Seawater / analysis*

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