pH buffer solution (4, 7 and 9)
€5.95*
Available, delivery time: 1-4 days
For calibrating pH combination electrodes (standardised to 20 °C)
Why calibration/adjustment?
The electronics of the pH meter must be adapted to the characteristics of the pH electrode used by calibration. Not only do different electrodes differ from each other (zero point, slope), but one and the same electrode also changes due to ageing processes.
Accurate and reproducible pH measurements are therefore only possible if calibration is carried out regularly and carefully.
How often this process is necessary depends of course on the location and purpose of use. If you measure under strongly changing conditions, calibration is recommended before each measurement.
For continuous measurement in the aquarium, it is sufficient to calibrate at intervals of 2 - 4 weeks if nothing else has changed. A new electrode or a measuring chain will change more at the end of its service life and calibration will therefore be necessary more often than in the middle of the expected service life.
Selection of buffers
For two-point calibration, the two pH buffer solutions are selected so that the pH to be measured is as close as possible between the values of the two buffers.
The option of calibrating with pH 4 and pH 9 in order to cover the entire pH range is only apparently favourable. Due to non-linearities of the measuring chain and the measuring amplifier, however, it leads to larger errors.
Temperature dependence of the pH at different temperatures
As can be seen, it is very important to pay attention to the correct temperature during calibration.
| Temperature | Buffer pH 4 | Buffer pH 7 | Buffer pH 9 |
|---|---|---|---|
| 0 °C | 4,03 | 7,13 | 9,24 |
| 10 °C | 4,02 | 7,05 | 9,11 |
| 20 °C | 4,00 | 7,00 | 9,00 |
| 30 °C | 4,00 | 6,98 | 8,93 |
| 40 °C | 4,00 | 6,97 | 8,86 |
| 50 °C | 4,00 | 6,96 | 8,80 |
| 60 °C | 4,00 | 6,96 | 8,75 |
| 70 °C | 4,00 | 6,97 | 8,71 |
| 80 °C | 4,00 | 6,98 | 8,67 |
| 90 °C | 4,00 | 7,00 | 8,64 |
Handling buffer solutions
Buffer solutions must be handled with care to ensure accurate calibration. Any contamination must be avoided.
Therefore, never pour buffer solutions back into the storage bottle, nor calibrate directly in the storage bottle. Used buffer solutions are discarded and not used a second time.
With alkaline buffer solutions (pH > 7), the CO2 from the air causes a gradual neutralisation of the buffer. The storage bottles should therefore be resealed immediately after use and contact with air should be minimised.
Composition of the buffer solutions offered
pH 4 (20 °C) d204 = 1.007 (~ 0.056 m citric acid solution / ~ 0.068 m NaOH solution / ~ 0.044 m NaCl solution)
pH 7 (20 °C) d204 = 1.006 (~ 0.029 m NaOH solution / ~ 0.050 m KH2PO4-solution)
pH 9 (20 °C) - blue coloured - borate-free - carbonate buffer
(NaOH - sodium hydroxide, NaCl - common salt, KH2PO4 - potassium dihydrogen phosphate, HCl - hydrochloric acid)
The solutions and chemicals used are (at least in small quantities) not Nevertheless, the electrodes should be thoroughly rinsed with demin. water before measuring again in the aquarium. The buffer and rinsing solution can be poured directly into the drain.
Rosenstraße 22
71101 Schönaich
Germany
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13 July 2025 00:00
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