Very Low pH Glass Electrode calibration

The program VLpH is designed for use in the calibration of a glass electrode in terms of hydrogen ion concentration at very low pH, where deviations from the Nernst law are observed. The electrode response is assumed to follow a modified Nernst law, eq. (1), in which E is a measured electrode potential, E⁰ is the "standard" electrode potential, s is a slope factor and jp is a "junction potential" correction factor.

E = E0 + s log10[H+] + jp [H+]

(1)

The calibration process is accomplished in two stages.

1. Perform a "titration", by adding a strong acid of known concentration to a known quantity of background electrolyte solution and measure the electrode potential at each titration point. Use VLpH to determine the calibration parameters, E⁰, s, and jp. [H⁺] is calculated from the amount of acid added, and its strength.
   
   
   
2. Read a set of data points from an experimental titration curve (obtained using the same background electrolyte) into VLpH. Adjust the values such that they will appear to obey the Nernst Law, eq. (2) and export the adjusted data, to Hyperquad, for example.

Eadj= E - jp [H+] = E0 + s log10[H+]

(2)

The program VLpH is available for download, free of charge. Simply click on the link below. The installation pack includes a help file (including details of experimental procedures) and examples of calibration data and data for adjustment. Comments and queries to: enquiries@hyperquad.co.uk

Download VLpH installer (self-extracting installation file)

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