WTW SenTix 21 PH Electrode, Plastic Shaft, Gel Electrolyte, BNC Connector, 103631

Anyone who measures pH levels on a daily basis in waste water, aquarium water or at a training centre needs an electrode that combines ease of use with robust technology. The SenTix 21 pH electrode from WTW is designed precisely for this purpose: a plastic shaft, a maintenance-free gel electrolyte and a BNC connector that can also be used with measuring instruments from other manufacturers.

Plastic shaft with maintenance-free gel electrolyte

The shaft is made of plastic (PPE/PS) and is therefore more resistant to impact than a glass electrode. The gel electrolyte is filled at the factory and does not need to be refilled; the fibre diaphragm establishes the electrical contact with the sample solution. The membrane resistance is less than 1 GOhm; the measuring range covers the entire pH scale from 0 to 14 at temperatures between 0 and 80 °C.

BNC connector for flexible use

The SenTix 21 does not have an integrated temperature sensor and is connected via a 1 m long fixed cable with a BNC connector (coaxial connector to DIN 19262). Without the additional banana plug for a temperature signal, it can also be used with simpler measuring instruments and devices from other manufacturers featuring a suitable coaxial input, provided that the temperature is entered manually or recorded separately. Its robust, straightforward design also makes the electrode particularly suitable for training and teaching environments, where electrodes often have to withstand frequent changes of hands and less careful handling.

Typical applications

According to WTW, the SenTix 21 pH electrode is suitable for, amongst other things:

• Electroplating effluent and industrial wastewater
• Aquarium and swimming pool water
• Groundwater, lake water, surface water and seawater
• Household cleaning products and general wastewater samples

Storage and shelf life

Between two measurements, the measuring chain should ideally remain immersed in reference electrolyte (3 mol/l KCl, Ag⁺-free). Overnight or during longer breaks, the clean electrode should be placed in the wetting cap filled with reference electrolyte; storing it in a dry place or in deionised water will cause permanent damage to the membrane. Once the irrigation cap has dried out, the measuring chain requires at least 24 hours of conditioning in fresh reference electrolyte before it can measure reliably again. WTW classifies pH measuring chains as consumables: strong acids and alkalis, hydrofluoric acid, organic solvents, oils, fats and high temperatures further reduce their service life.

Distinctions within the SenTix family

Within the WTW electrode range, the SenTix 21 differs from the SenTix 41 (item no. 103635), which uses the same plastic shaft and the same gel electrolyte but also features an NTC temperature sensor and a DIN connector with banana plugs. Those wishing to use automatic temperature compensation on the measuring instrument are better served by the SenTix 41. For more demanding requirements regarding media and measurement range, for example, in pharmaceutical analysis or for samples up to 100 °C, the SenTix 81 glass electrode (item no. 103642) is the more suitable choice.

Design and response behaviour

The fibre diaphragm forms the interface between the reference electrolyte and the sample solution. It is less susceptible to blockages than a ceramic diaphragm and is therefore also suitable for samples containing suspended solids or organic residues, such as those found in waste water or aquarium water. WTW does not specify a precise numerical response time for the SenTix 21, either on the product page or in the user manual; in practice, however, it remains sufficiently short for routine measurements of this type.

A common example is checking a swimming pool or aquarium: the electrode is briefly immersed, provides the measurement value on the spot, and can then be reinserted into the protective cap without any further preparation for the next use.

Technical details

Scope of delivery

• 1 WTW SenTix 21 pH electrode with hydration cap fitted
• Operating instructions available for download

Individual requirements and procurement service

For calibration, the WTW technical buffer solutions pH 4.01 (item no. 108706) and pH 7.00 (item no. 108708) from the same manufacturer are suitable. If you require further accessories, replacement electrodes or have any questions regarding the appropriate SenTix model, the LT Laborhandel procurement service is available at lt-laborhandel.com/service.