The saturated calomel electrode (SCE) is a classic reference electrode in which mercury and mercury(I) chloride (calomel) are in contact with saturated KCl solution. Its potential is about 44 mV more positive than a saturated-KCl Ag/AgCl (+0.241 V vs. SHE at 25 °C). Because KCl is used, K⁺ and Cl⁻ move at similar speeds across the junction, which keeps the liquid junction potential small.
Because it contains mercury, most laboratories have moved to Ag/AgCl; the SCE is still chosen for results comparable with older literature, teaching laboratories and for checking other reference electrodes. Do not use it above 50 °C. In acidic or alkaline solutions choose the double salt bridge model. It contains mercury: do not break it and dispose of it as hazardous waste.
| Electrode type | Saturated calomel reference electrode (Hg/Hg₂Cl₂), Hg₂Cl₂ + 2e⁻ ⇌ 2Hg + 2Cl⁻ |
| Internal filling solution | Saturated KCl |
| Potential (vs. SHE, 25 °C) | +0.241 V |
| Difference to saturated-KCl Ag/AgCl | About +44 mV more positive (0.241 V − 0.197 V) |
| Suitable media | Neutral aqueous systems |
| Acid-base systems | Double salt bridge model (217) recommended |
| Temperature limit | Use above 50 °C is not recommended (Hg₂Cl₂ becomes unstable) |
| Chloride interference | Chloride leaks from the electrode; in chloride-sensitive systems use a chloride-free salt bridge or choose Hg/Hg₂SO₄ |
| Junction clogging | KClO₄ can precipitate in perchlorate-containing electrolytes; ions such as Ag⁺, Hg²⁺ and Pb²⁺ can precipitate with chloride |
| Storage and care | Do not let the tip dry out; store in saturated KCl solution |
| Hazard note | Contains metallic mercury and mercury(I) chloride; do not break the body, collect waste separately as hazardous waste |
| Model | Description |
| 232 Standard | Single salt bridge, standard length |
| 232 Long | Single salt bridge, extended length |
| Slim 3.8 mm | Slim 3.8 mm diameter body |
| 217 Double Salt Bridge | Double salt bridge design |
| 1545 | Single salt bridge, short body |
For sizes and specifications not listed above, you can request a custom quotation through the Quote Form.
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