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By Hanna Instruments, Inc.
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Fundamentals of pH Measurement
๐ pH, or potential of hydrogen, is the second most tested parameter after temperature in many applications.
๐งช pH is measured on a logarithmic scale from 0 to 14, where 7 is neutral; below 7 is acidic ( activity > activity), and above 7 is basic ( activity > activity).
๐ Because the scale is logarithmic, a reading difference of 1 pH unit represents a 10-fold difference in ion concentration.
๐ก๏ธ pH readings are sensitive to temperature, meaning the measured pH at one temperature may differ from another, requiring temperature compensation.
Components of a pH Measuring System
๐ A complete system consists of a pH sensing half-cell, a reference electrode half-cell (often combined into a single electrode today), a meter, and the sample solution.
๐ง The combined pH electrode features a sensing glass tip whose condition is vital; damage to the thin binding layer cannot be repaired.
โก The electrode creates an electrochemical circuit by measuring the charge on the glass tip relative to an internal reference solution.
๐ The electrode is a consumable item, as the binding layer degrades over time, necessitating eventual replacement.
Selecting the Right pH Electrode
๐ฌ Key electrode design factors include glass type, junction material, body material, and sensing bulb shape.
๐ก๏ธ Glass Types range from general purpose to specialized options like low-temperature, high-temperature, and HF-resistant glass (for fluoride ion environments).
๐ Bulb Shapes include spherical (general aqueous use), conic (for penetration into soils/gels/meats), and flat-tip (for direct surface measurement like skin or paper).
๐ Junction Types (the electrical pathway) are critical; options include porous ceramic frit (common), PTFE (chemically resistant), fiber wick (for quick refresh), and open junction (high flow rate for clogging samples).
pH Meter Types and Calibration Requirements
๐ pH meters range from inexpensive testers (for hobbyists/spot-checks) to portable handheld meters (with data logging) to high-accuracy benchtop meters (for stationary lab use).
๐ ๏ธ Calibration is required after long disuse, rehydrating a dried electrode, or cleaning, with daily calibration recommended for best accuracy.
๐ When calibrating, use buffer solutions that bracket the expected sample reading (e.g., use and if the sample is expected to be near ).
๐ For refillable electrodes, the fill cap must be removed during measurement and calibration to ensure the electrolyte flows through the junction and closes the circuit.
Measurement and Electrode Care Procedures
๐ง Always rinse the electrode with deionized (DI) water between solutions (calibration buffers or samples) to prevent cross-contamination.
๐๏ธ When using a magnetic stirrer during measurement or calibration, ensure the speed is correct: stir gently, avoid aggressive stirring or creating a vortex that breaks contact with the bulb/junction.
๐งผ Post-measurement, electrodes must be cleaned (using appropriate solution if necessary) and then stored completely submerged in storage solution to maintain function and lifespan.
Key Points & Insights
โก๏ธ pH testing relies on measuring tiny ion concentrations via a delicate electrochemical circuit that is sensitive to temperature.
โก๏ธ When selecting an electrode, prioritize the junction type based on the sample's tendency to clog the junction (e.g., use PTFE or open junction for difficult samples).
โก๏ธ For accurate calibration, choose buffers that bracket the expected pH value and ensure the electrode junction is fully submerged during all steps (rinsing, calibration, and measurement).
โก๏ธ Proper storage in storage solution when not in use is mandatory for electrode longevity and maintaining fast, accurate response times.
๐ธ Video summarized with SummaryTube.com on Mar 11, 2026, 14:25 UTC
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