The E-331D is a sealed gel-filled composite pH electrode with Ag/AgCl reference system and fiber junction. pH range 0–14, temperature range 0–80°C, accuracy 0.01 pH. PC shaft, Φ12×105mm, BNC connector. The standard pH electrode supplied with all Skill Scientific benchtop and portable pH meters.
The E-331D composite pH electrode is the standard sensing accessory supplied with Skill Scientific pH meters. As a composite (combination) electrode, it integrates both the pH-sensitive glass membrane and the Ag/AgCl reference electrode into a single body — eliminating the need for a separate reference electrode and simplifying day-to-day operation in the laboratory and field.
The E-331D uses a sealed Ag/AgCl gel reference system. Factory-sealed gel electrolyte eliminates the need for periodic refilling of reference solution during normal service life, reducing maintenance requirements and making the electrode suitable for use in any orientation — including horizontal and inverted positions where liquid-filled electrodes would leak. The fiber junction provides a stable, low-resistance liquid junction contact between the reference electrolyte and the sample solution, ensuring reliable, drift-free readings across the 0–14 pH range.
The polycarbonate (PC) shaft (Φ12×105mm) is lightweight and resistant to accidental breakage compared to glass-bodied electrodes, making it well suited to busy laboratory environments and general-purpose use. The BNC connector is compatible with all Skill Scientific pH meters as well as most other laboratory pH instruments.
The E-331D is included as standard with the pHS-3, pHS-4, pHS-5, pHS-3C, pHS-3CT, pHS-3C, pHS-2C, pHS-25, pHB-7, pHB-4 and other Skill Scientific pH meters, and is available separately as a replacement electrode.
| Model | E-331D |
| Description | pH Composite Electrode (Sealed) |
| pH Range | 0 – 14 |
| Accuracy | 0.01 pH |
| Shaft Material | PC (Polycarbonate) |
| Reference System | Ag/AgCl Gel (Sealed) |
| Junction Type | Fiber |
| Temperature Range | 0 – 80°C |
| Dimensions | Φ12 × 105 mm |
| Connector | BNC |
A composite (or combination) electrode integrates the pH-measuring glass membrane and the reference electrode into a single unit. Traditional pH measurement requires two separate electrodes — a glass pH electrode and a reference electrode — which must both be connected to the meter and immersed in the sample. A composite electrode combines both functions in one body with a single BNC connector, simplifying setup, reducing the risk of connection errors and making it suitable for small sample volumes.
The E-331D uses a factory-sealed Ag/AgCl gel as the reference electrolyte, rather than a liquid KCl solution that requires periodic refilling. Sealed gel electrodes require no maintenance refilling during their service life, can be used in any orientation without leakage risk, are less susceptible to junction clogging from sample contamination, and are generally more convenient for routine laboratory and field use. The trade-off compared to refillable electrodes is that once the gel is exhausted or contaminated, the electrode must be replaced rather than refilled.
Under normal laboratory use, the E-331D typically provides 12–18 months of service life. Service life is affected by frequency of use, sample types (highly acidic, alkaline or contaminated samples shorten electrode life), storage conditions and calibration frequency. Signs that the electrode needs replacement include slow or unstable response, inability to calibrate within acceptable slope range (typically 95–105%), asymmetry potential drift and physical damage to the glass membrane or shaft.
For short-term storage (overnight to a few days), keep the electrode tip immersed in pH 4.00 buffer solution or 3 mol/L KCl storage solution — never in distilled or deionised water, which will cause the reference gel to dehydrate. For long-term storage, use the protective cap filled with a small amount of storage solution. Before use after storage, allow the electrode to equilibrate in buffer solution for 5–10 minutes before calibrating.
Replace the electrode when: the calibration slope falls outside 90–110% of theoretical (indicating degraded glass membrane sensitivity); readings are consistently unstable or slow to stabilise even after cleaning and reconditioning; the calibration offset (asymmetry potential) is excessively large; or when there is visible physical damage to the membrane tip or shaft. The electrode monitoring function on Skill Scientific touchscreen pH meters (pHS-3, pHS-4, pHS-5, pHB-7) alerts the operator when electrode performance deteriorates below acceptable thresholds.
Yes. The E-331D uses a standard BNC connector and is compatible with most laboratory pH meters from all major manufacturers that accept BNC pH electrodes. It meets the standard composite electrode specification for pH range, impedance and connector type, making it a practical replacement electrode for non-Skill Scientific instruments as well.
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