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pH Electrodes for the laboratory

We offer pH electrodes or combination electrodes for pH measuring devices from Agilent Technologies, Mettler Toledo and WTW. The electrodes can be used in a wide range of applications such as pH measurements in food testing. The chemical composition, homogeneity, temperature, process pressure and the pH range of the sample are important criteria when choosing the right electrode. Contact our customer service to assist you on selecting the right electrode.

A pH electrode selection guide can be found here.

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  1. WTW

    Conductivity electrode TetraCon 325

    sku: WW301960
    In Stock
  2. Mettler-Toledo

    pH electrode LE438 (plastic, 3-in-1)

    sku: MR51340242
    In Stock
  3. Mettler-Toledo

    pH combination electrode InLab Micro

    sku: MR51343160
  4. WTW

    SenTix 61 standard pH combination electrode

    sku: WW103640
    In Stock
  5. Mettler-Toledo

    pH combination electrode InLab Easy

    sku: MR51343010
    In Stock
  6. Mettler-Toledo

    pH combination electrode InLab Routine

    sku: MR51343050
  7. Mettler-Toledo

    pH combination electrode InLab Routine Pro

    sku: MR51343054
    In Stock
  8. Mettler-Toledo

    pH combination electrode InLab Routine Pt1000

    sku: MR51343056
    In Stock
  9. Mettler-Toledo

    pH combination electrode InLab Science

    sku: MR51343070
  10. Mettler-Toledo

    pH combination electrode InLab Routine Expert Pro

    sku: MR51343101
    In Stock
  11. WTW

    SenTix 21 basic pH combination electrode

    sku: WW103631
    In Stock
  12. WTW

    SenTix 22 basic pH combination electrode

    sku: WW103633
    In Stock
  13. WTW

    pH combination electrode SenTix 41-3

    sku: WW103636
    In Stock
  14. WTW

    SenTix Sp Spear-type pH-combination electrode

    sku: WW103645
    In Stock
  15. WTW

    SenTix ORP ORP combination electrode

    sku: WW103648
    In Stock
  16. WTW

    SenTix® 51 combined pH-electrode

    sku: WW103651
  17. WTW

    SenTix® 52 combined pH-electrode

    sku: WW103652
    In Stock
  18. WTW

    SenTix 940 combined pH sensor, digital

    sku: WW103740
    In Stock
  19. WTW

    SenTix® ORP-T 900 ORP electrode, digital

    sku: WW103791
    In Stock
  20. WTW

    Oxygen sensor (galvanic) CellOx 325

    sku: WW201533
  21. WTW

    WP 90/3 3 exchange membrane heads

    sku: WW202725
    In Stock
  22. WTW

    pH-Combination electrode Sensolyt

    sku: WW109115
  23. Mettler-Toledo

    pH-Elektrode InLab Solids Pro IP67

    sku: MR51343156
  24. Mettler-Toledo

    FiveEasy Benchtop F20 pH/mV Meter (Entry-Level)

    sku: MR30266658
  25. Mettler-Toledo

    pH combination electrode InLab Easy BNC

    sku: MR51343011
  26. Mettler-Toledo

    pH combination electrode InLab Routine Expert

    sku: MR51343100
  27. Mettler-Toledo

    pH combination electrode InLab Routine Expert NTC30

    sku: MR51343104
  28. Mettler-Toledo

    pH combination electrode InLab Power

    sku: MR51343110
  29. Mettler-Toledo

    pH combination electrode InLab Solids

    sku: MR51343153
  30. Mettler-Toledo

    pH combination electrode InLab Semi-Micro

    sku: MR51343165
  31. Mettler-Toledo

    pH combination electrode InLab Hydrofluoric

    sku: MR51343176
  32. Mettler-Toledo

    InLab® Ultra Micro-ISM

    sku: MR30244732
  33. Mettler-Toledo

    pH-Elektrode LE438-IP67

    sku: MR30247153
  34. WTW

    SenTix Mic-D combined pH-electrode

    sku: WW103660
  35. WTW

    SenTix HWD pH electrode

    sku: WW103731
  36. Mettler-Toledo

    InLab® Surface Pro-ISM

    sku: MR30249570
  37. Mettler-Toledo

    LE409-DIN pH electrode with glass shaft,

    sku: MR51340343
  38. Mettler-Toledo

    InLab413, IP67, pH electrode

    sku: MR51340288
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pH electrodes selection guide

What is required for pH measurements?

A special measuring tool for hydronium ions which the pH value refers to, is required to measure the pH value. The principle of the measurement is based on a sensor with a glass membrane, which selectively detects hydronium ions and registers the reaction between the membrane and a sample solution. This glass electrode potential alone does not provide sufficient information, a second sensor is thus required which provides the reference potential for the pH sensor. To determine the pH value of the solution, the potential difference between these electrodes must be measured.

The reaction of the pH-sensitive glass electrode depends on the concentration of the H+ ions (or H3O+). Hence, pH is a measurement of both acidity and alkalinity, a selective measurement of hydronium ion activity. On the other hand, the reference electrode does not react to the concentration of the H+ ions in the sample solution and always delivers the same constant potential which is used to measure the potential of the pH sensor. The difference in potential between the two electrodes determines the pH of the solution. Since this potential is a linear function of the hydronium ion concentration in the solution, the concentration can be measured quantitatively.

Nowadays, the pH sensor and the reference sensor are very often housed in one electrode. This combination of reference and pH electrode is called a combined pH electrode. Each of these three types of electrodes is different and has its own characteristics and properties.

pH electrodes

The pH electrode is the component that actually registers the pH of the solution. It consists of a glass shaft with a thin glass membrane at the lower end that is H+ ion sensitive. When this membrane comes into contact with an aqueous solution, the outside of the membrane glass forms a gel layer. A similar gel layer is also formed on the inside of the membrane glass as the electrode is filled with an internal aqueous electrolyte solution.

The H+ ions in and around the gel layer can - depending on the pH value and thus the H+ ion concentration of the measurement solution - either diffuse into or out of the layer. If the solution is alkaline, the H+ ions diffuse out of the layer and a negative charge is created on the outside of the membrane. Since the glass electrode has an internal buffer with a constant pH value, the potential on the inner surface of the membrane remains constant during the measurement. The potential of the pH electrode is therefore the difference between the inner and the outer charge of the membrane.

Reference electrodes

The task of the reference electrode is to provide a defined stable reference potential against which the potential of the pH sensor can be measured. To achieve this, the reference electrode must be made of glass, which is not sensitive to the H+ ions in the solution. It must also be open to the sample environment in which it is immersed. An opening or a diaphragm is made in the shaft of the reference electrode through which the inner solution or the reference electrolyte can flow into the sample. To obtain correct measurements, the reference electrode and the pH half-cell must be in the same solution.

The electrode construction consists of an inner reference element that is immersed in a defined reference buffer solution and has indirect contact with the sample solution via the diaphragm. This contact chain ensures a stable potential. There are several reference systems available, but the silver/silver chloride system is now used almost exclusively in laboratories. The potential of this reference system is defined by the reference electrolyte and the silver/silver chloride reference element. It is important for the reference electrolyte to have a high ion concentration and a low electrical resistance.

As the reference electrolyte flows into the sample during the measurement, pay attention to possible reactions between the reference electrolyte and the sample solution. Such reactions could affect the electrode and measurement.

Combined electrodes

Combined electrodes are much easier to handle than two separate electrodes and are therefore used very frequently today. In the combined electrode, the pH-sensitive glass electrode is surrounded concentrically by the reference electrode, which is filled with the reference electrolyte. The pH and reference components of the combined electrode have the same properties as the corresponding separate electrodes. The only difference is that they are integrated in a single electrode for easier handling. The use of individual pH and reference electrodes instead of a single combined electrode is only recommended if the two components of the combined electrode have a very different expected life span.

To further simplify pH measurements, a temperature sensor can be used together with the pH and the reference element in the same shaft. This enables temperature compensation while measurung pH. Such electrodes are also referred to as 3-in-1 electrodes.

pH and redox electrodes for every application

Electrodes may consist of different materials (very common are platinum, calomel or hydrogene electrodes) and are hence very versatile. They are knowned as single-rod measuring cells which are used to determine the pH value. However, the standard hydrogene electrode serves here as the reference electrode to determine the standard potential of redox couples. The most common ones are solid state electrodes containing of a metal and its dilution. Liquid electrodes such as quicksilver electrodes can also be used. 

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