Conversions between scales of different reference electrodes

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Conversions between scales of different reference
electrodes
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Line diagram of the glass electrode
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Combination glass electrode with silver-silver
chloride reference electrode
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Additional models of combination pH electrodes.
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Ion-exchange process across the glass membrane of
the glass electrode
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• The voltage response of the glass electrode is
  linear with the pH (or log aH) as shown in
  equation 14-6.
• E constant ?(0.05916)?pH
• The value of ? (the slope of E vs pH) is
  generally 1.0. The constant is the asymmetry
  potential and arises from the differences in the
  two sides of the glass membrane. The asymmetry
  potential is corrected by calibration of the
  glass electrode against a pH buffer solution of
  known pH.

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In order to use the glass electrode to make
meaningful measurements you need to note

• standardize with standard pH buffers
• junction potentials minimize effects by matching
  the ionic composition of the unknown to standards
  if possible.
• Drift of junction potentials recalibrate as
  needed
• Na error
• Acid error
• Equilibration (response time)
• Hydration of the glass membrane
• Temperature

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Acid and sodium errors
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Solid-state pH probe
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Ion-selective electrodes The Fluoride electrode
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Calibration curve for the fluoride electrode
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Diagram of the Calcium ion-selective electrode
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Compound electrodes are conventional electrode
systems surrounded by a membrane that reacts in a
specific way with an analyte. Pictured here is
the CO2 gas sensing electrode.
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