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The Advantages of Gel-filled pH Electrodes

Knowing the pH of different solutions is important for avoiding human health risks and ensuing environmental safety. Potentiometric pH measuring involving the use of pH electrodes was commercialized in the 1950s, replacing earlier methods such as tasting the solutions. Many technological improvements have since been made to pH electrodes, and there are several types available.

  1. Theory

    • Acidity or alkalinity of a solution is measured via a pH scale ranging from 0 to 14. In calculations, pH is defined as the negative base 10 logarithm of hydrogen ion concentration. At a neutral pH 7, acid and alkali concentrations are equal at 10E-7. At an acidic pH of 0, hydrogen ions are highest at 10E0, while at high alkalinity, hydrogen ion concentration measures at 10E-14. The pH electrodes are designed according to this theory.

    Circuit

    • The pH circuit measures the potential difference between two electrodes in solution, and is calculated in millivolts. Two electrodes are involved in a pH circuit. The reference electrode not only completes the circuit but provides a constant reference potential, irrespective of the electrolyte solution properties. The measuring electrode develops a potential directly proportional to the pH of the electrolyte solution.

    Maintenance Advantages

    • Gel-filled electrodes have a wide range of applications, including use in clean and dirty water. Their ease of installation and maintenance is behind this multipurposing, because gel-filled electrodes do not require refilling. As a result, they require fewer calibrations and demonstrate greater stability. With continued use, the electrodes eventually become transparent, and the transparent zone marking on the shaft is a convenient indicator that the electrode needs replacing.

    Other Advantages

    • Compared with liquid-filled electrodes, the electrolyte flow rate across the pin-type junction of gel-filled electrodes is substantially less, giving them a longer life span. Gel-filled electrodes are also smaller than other electrodes, which makes them more economical. Gels also maintains zero potential for longer time periods, and have an improved response time to equilibrium, particularly at low temperatures. This improves accuracy and limits errors in samples with differing ionic strengths.

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