RESEARCH ARTICLE

 

Glass electrode calibration for use in the voltammetric determination of stability constants under extreme acidic conditions

 

 

Caren Billing^I; Ignacy Cukrowski^II

^ISchool of Chemistry, University of the Witwatersrand, P. O. Wits, Johannesburg 2050, South Africa
^IIDepartment of Chemistry, University of Pretoria, Pretoria 0002, South Africa

 

 

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ABSTRACT

A glass electrode (GE) can be successfully employed to measure pH in the study of metal-ligand equilibria by voltammetry at extremely low pH (between 0 and 2); two consecutive strong acid-strong base titrations involving different base concentrations (recommended to avoid corrosion of the GE in very basic solutions) are best suited to establish the response parameters of a GE. A novel approach of using a combined linear and binomial GE calibration was developed; this procedure allows measurements between pH 0 and 2 with uncertainty better than ±0.01 pH unit. From an extensive error analysis, it has been established that the uncertainties of about ±0.5 mV in the response slope and ±1.3 mV in E°' might result in an absolute error in pH of about 0.02 which should not generate errors larger than 0.3 % in optimized stability constants (as log K values) determined by voltammetry at extremely low pH. A test of GE suitability for the study of metal complexes by voltammetry is also proposed; it should be implemented only for suspect electrodes that show response parameters outside the limits recommended in this work.

Keywords: Glass electrode calibration, glass electrode performance, use of GE in highly acidic media, metal-ligand equilibria studies, potentiometry, voltammetry

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Acknowledgements

The authors thank the National Research Foundation (NRF), the University of the Witwatersrand and the University of Pretoria for their financial support.

 

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Received 26 May 2009
Revised 25 August 2009
Accepted 30 September 2009

 

 

* To whom correspondence should be addressed. E-mail: ignacy.cukrowski@up.ac.za