Maintenance and the life time of the ph meter
This question brings out another question; how accurate do you want to be? As no application is the same, here is a good way to know when calibration is due: Procedure Perform a calibration on day 1. On the following day, simply soak your electrode in the original buffers you performed calibration with and note the readings. If the readings are still within your expectations, keep doing this procedure everyday until you are not happy with the accuracy. Then proceed to calibrate and take note of the number of days that went by since day 1 of calibration. If 5 days went by, proceed to calibrate every 4-5 days. As the pH electrode gets older, proceed to do this test monthly to confirm number of days required between calibrations. This is also a good way to forecast probe cleaning or replacement.
The lifetime of a pH electrode depends on several factors including storage conditions, correct maintenance and the type of sample measured. Under normal laboratory conditions, for aqueous samples, the average lifetime is between 12 and 18 months, supposing of course that the electrode is kept clean and kept hydrated during storage. If the probe is used with dirty samples (e.g. stirred solutions with particles), is subjected to mechanical abrasion or used at high temperature or high pressure, the lifetime may be only a few weeks. In hot alkaline solutions, pH probes can be damaged after only a few hours. Regular maintenance helps pH probes keep working efficiently for several years.
This may be caused by one of the following: - the glass membrane or the diaphragm is dirty, e.g. oil, fat, paint, dirt. - the pH probe is reaching the end of its lifetime. If the probe is dirty you will notice bubbles forming around in certain areas when taking readings. If meter has not been properly taken care of or it has been 12 months, it might be time to change the meter or the probe.
pH electrodes need to be kept wet in order to keep the glass sensitive part in good condition. If the glass sensitive part dries out for more than 6 months, the pH electrode will die. If it dries out for a few months, it can be regenerated by soaking into storage solution overnight (4.01). The storage solution brings and keeps a constant ion activity in the sensing part that will assure fast response and accurate readings. Always store your pH electrode after your series of tests are done. Electrodes that are not stored into storage solution will show slow response and fluctuations in readings.
Many people think that pure water is good for pH electrodes. This is wrong. Pure water actually kills pH electrodes by sucking its electrolyte out of the reference chamber. Pure water is excellent for rinsing between samples, but harmful for storage purposes. If you are out of storage solution, a pH 4.01 buffer can be used for a few weeks. Long term storage into pH buffers is not recommended as they contain phosphate.
It is difficult to know the exact time to take a pH reading. In general, one minute is required to obtain a stable reading. If a reading is taking an exceptionally long time to stabilize, this can indicate several conditions: a clogged electrode junction, a non-homogeneous solution, a troublesome sample with low ionic strength, or a non-aqueous sample.
Yes. There are two main advantages to slowly stirring or gently agitating the sample during a pH measurement. First, the increased flow of the sample across the electrode results in a faster response time. Second, the solution is properly homogenated so no areas of increased or decreased pH exist.
It is advisable to use a specific pH probe with a strong glass tip and high electrolyte outflow. Mix a 5 g soil sample with 25 g deionized water while stirring carefully. Then let the mixture stand without stirring for 10 minutes to separate the particles from the liquid. Insert the pH probe in such a way that the glass bulb is totally covered by particles, but the diaphragm is not. Wait for a stable reading.
Yes, but for best results, we recommend rinsing with deionized water then conditioning the probe in pH 4.0 buffer for at least 2 hours. After further rinsing, it is ready to be calibrated. The normal (quick) response time will be achieved after 24 hours hydration. If measurements are needed before this time, calibrations should be repeated often due to drifting potentials.
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