In order to obtain permanently accurate measured values, the equipment must be constantly maintained – this also includes cleaning the pH electrode. Find out what to look for when storing, what types of contamination can occur, and what steps are ideal for cleaning and caring for your pH electrode.
Proper cleaning of the pH electrode begins with storage
PH electrodes represent sensitive technical measuring instruments that require special cleaning and storage. In fact, cleaning begins with storage – so the service life can be significantly increased by proper maintenance and care.
Combination electrodes and reference electrodes have a reference electrode with electrolyte liquid. The corresponding liquid electrolyte electrodes should be kept in the same aqueous solution, and for gel electrodes, for example, 3 mol/l KCl solution is ideal. Glass electrodes, on the other hand, require storage in deionized water.
In addition, a distinction can also be made in the duration of retention. This can be classified as follows:
- Short-term storage: In tap water (never in distilled water!) or directly in the storage solution.
- Medium-term storage: From several days, storage in the storage solution is necessary.
- Long-term storage: If storage lasts for several weeks or months, dry storage can also be used.
Although, in principle, short-term dry storage is also possible, the functionality of the pH electrode can be significantly impaired. Before the next use, it must be soaked for several hours in a storage or buffer solution with a pH of 4 or 7. After that, a new calibration is also necessary.
Regular maintenance and cleaning of the pH electrode requires the use of a cleaning solution. This works gently and at the same time efficiently to free the device from contamination without the need for mechanical rubbing. Typical cleaning solutions can be divided into standard solutions for common uses and inspecific solutions.
Standard solutions for cleaning the pH electrode
Standard solutions are often used and take care of contaminants that are regularlyfound on pH electrodes. These include, in particular, the following representatives:
- Alkaline surfactant and polyphosphate solution, sodium hypochlorite solution or phosphoric acid:electrode rinsing, general application and universal cleaner.
- Ethanol, acetone or alkaline surfactant and polyphosphate solution: Greases and oils
- Pepsin/HCl solution:Proteins
- HCl or caustic soda solution:Inorganic substances
Specific solutions for cleaning the pH electrode
The situation is somewhat more specialized in the case of soiling caused by certain areas of application. Here, too, a differentiation can be made betweenvarious cleaning solutions that are up to the task at hand. Common examples include the following spills:
- Ethanol, acetone or alkaline surfactant and polyphosphate solution:Meat fat
- Ethanol, acetone, sodium hypochlorite solution, pepsin in HCl, thiourea solution or HCl:blood products (which is why the solution must be disinfectant).
- Sodium hypochlorite solution, pepsin in HCl, thiourea solution or HCl: beer and wort residues.
- Sodium hypochlorite solution, pepsin in HCl, thiourea solution or HCl: milk sediment and dairy products (such as cheese and yogurt).
- Alkaline surfactant and polyphosphate solution, phosphoric acid or HCl:soil and hummus residues.
- Ethanol, acetone or alkaline surfactant and polyphosphate solution:Ink stains
- Sodium hypochlorite solution: bacteria, algae and fungi (disinfectant)
Cleaning the PH electrode in 5 steps
Optimal cleaning of a pH electrode consists of several steps. It is important that this is started immediately after use to directly prevent dirt buildup on the membrane surface, the diaphragm and in the interior. The following steps serve as orientation:
- Rinsing:After measurement, the electrode should first be rinsed with distilled water to remove any superficial residues of the measuring solution.
- Immersion: The pH electrode is then immersed in a suitable cleaning solution until the visible diaphragm appears clean. If the device was used in solutions containing albumin or sulfite (for example, in milk or yogurt), the electrode must be immersed until the diaphragm is white again.
- Replace electrolyte: Some electrodes allow the internal electrolyte fluid to be replaced. If this is possible, the replacement should be made at this point.
- Watering: The electrode is then soaked in the storage solution for two to three hours. If it is not to be used further afterwards, it can remain in the solution.
- Calibration: At regular intervals or after a longer storage period of the pH electrode, a new calibration should also be included as a cleaning step.
When cleaning the pH electrode, mechanical procedures (such as rags or brushes) should be avoided, as these could damage the sensitive surface of the electrode. Instead, theimmersion and watering intervalshould be extended if soils remain visible after cleaning.
Types of buildup and contamination
As briefly mentioned earlier, pH electrodes can be loaded with a variety of different buildup and contaminants. This factor depends on both the frequency of use, the type of electrode, and the test sample. The following table is intended to provide a brief overview of which specific cleaning methods are ideal in each case:
|Type of pollution||Basis of the detergent||Cleaning method|
|Inorganic||Alkaline surfactant and polyphosphate solution, sodium hypochlorite solution or phosphoric acid.||Rinse for 5 to 20 minutes|
|Organic||Ethanol, acetone or sodium hypochlorite solution||Rinse for 5 to 10 minutes|
|Proteins||Ethanol, acetone or pepsin in HCl||Rinse with ethanol and acetone for 5 to 10 minutes; rinse with pepsin in HCl for up to 30 minutes.|
|Sulfides||Alkaline surfactant and polyphosphate solution, thiourea solution or HCl||Rinse for 5 to 30 minutes|
|Electrolyte incrustation||Alkaline surfactant and polyphosphate solution||Rinse for 5 to 20 minutes|
|KCl crystals||Water||Heat the electrode in a water bath at about 45°C until the crystals dissolve by themselves. Afterwards exchange of the electrolyte solution|
|Contamination inside the reference electrode||n. A.||Exchange of the electrolyte solution. The cleaning effect can be increased by a warm electrolyte solution (about 45°C)|
Tips for care and cleaning of the pH electrode
To ensure that the pH electrode remains durable for a long time and displays consistent results, some important tips and tricksshould be taken into account when caring for it. In summary, these aspects look as follows:
Apart from the special case of permanent dry storage, electrodes should always be kept moist. Otherwise, there is a risk that they will react sluggishly and only display inaccurate measured values. Dry pH electrodes must be soaked in a storage solution before being used again.
Never wipe the electrode
Furthermore, the pH electrode should never be cleaned mechanically, e.g. by wiping. In addition to possible damage, this can also create a static chargethat can interfere with the pH measurement. For cleaning, it is therefore necessary to rinse with a suitable cleaning solution.
Storage in a storage solution
Storage in a storage solution not only contributes to the care and maintenance of the device, but also ensures that it is always ready for use. If distilled water were used instead, leaching of the ions in the electrolyte solution would occur. This accelerates the aging process and reduces the reactivity of the pH electrode.
Regular cleaning of the pH electrode can ensure that there are no visible or invisible deposits on the glass surfaceand diaphragm of the electrode. These would negatively affect the measurement and calibration. Therefore, cleaning should be performed step-by-step according to the above procedure.
Refilling or replacing the electrolyte solution
A sufficiently high filling levelof the electrolyte solution must be present for each measurement. If this is not the case, replacement becomes necessary. The same applies if contamination has occurred in the electrolyte. Otherwise, there is a risk of inaccurate measured values again.
Calibration of the pH meterensures the most accurate measurement possible and must be performed at regular intervals. A two-point calibration with two different buffer solutions is particularly common.
Condition check before and after use
Over time, the glass membrane of the electrode may become less sensitive or even stop working altogether. Mechanical damagemay also occur, making the probe unsuitable for measurement.
The correct cleaning of pH electrodes
To obtain an accurate reading, regular cleaning of the pH electrode is essential. The selection of a suitable cleaning solution plays a central role here. Optimum conditions should also be ensured during storage. Otherwise, measurement errors can quickly occur, which should of course be avoided at all costs.
The pH electrode is stored in a suitablestorage solution. Depending on the duration of storage, tap water, KCl solutions and sometimes dry storage are also possible.
Storage in KCl prevents water from entering the electrode by osmosis and diluting the electrolyte. This would change the potential of the reference element. Contamination is also prevented.
Usually, a pH probe is readjusted with a so-called two-point calibration. This requires two buffer solutions, one with a pH of 7 and the other with a pH of 4 or 10. The voltage difference is determined with a measuring device.
A pH electrode measures an electrical potential that is created between the reference electrode and the measured solution. From this, a potential difference can be generated which can be represented linearly as a pH value.
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