For best results, always keep the pH bulb wet, preferably in pH 4.01 buffer with 1/100 part of saturated KCl added. Obviously, this is a very sensitive instrument, and needs to be taken care of properly. The simplest thing that can be done is to keep the probe submerged in liquid. The special conductive glass coating shouldn’t be left to dry out… always keep it hydrated, or it may stop working! You can buy special storage solutions for this purpose. Either keep the probe submerged in a falcon tube, or keep the probe covered with the special cap it came with. The exact type of solution used will depend on your meter, as different probes have different requirements. Combined electrodes (those consisting of both the glass and reference electrodes) are typically stored in a concentrated solution of whatever is inside the probe – the concentration should be higher to prevent diffusion out of the probe. pH meters with two separate electrodes can have their glass electrodes stored in an acidic solution of roughly pH 3. In either case, never use distilled or deionized water, as prolonged submersion in water can encourage diffusion out of the electrode, which will affect its sensitivity Other pH buffers or tap water are acceptable storage media, but avoid storage in distilled water. The protective boot filled with buffer will provide an ideal storage chamber for long periods. NOTE: Electrodes should not be stored for a period longer than 6 months for best results. Electrode stock should be rotated accordingly.
Cleaning and Maintenance:
If your meter has been left to dry out and is now covered in dust and the crystallised remnants of whatever it was submerged in – you may want to consider getting it professionally serviced. It may still be ok, but could need a special treatment to get it working properly. Otherwise, if it’s in pretty good condition, there are things that can be done to keep it running smoothly. Special washes can be bought to treat the probes and can be used regularly (perhaps once a month or so, depending on how often the pH meter is used) to maintain the special conductive surface of the probe. Junctions in the meter may become clogged sometimes too – follow the manufacturer’s instructions for cleaning in these instances.
It’s also important to clean the electrode between uses – don’t just take it out of your solution you’ve been working with and put it back in the storage solution. Rinse the probe with distilled or deionized water (which is ok for washing and rinsing – just not for submersion!) and then dry it quickly by blotting (NOT wiping!) before submerging it in your next solution or returning it to the storage solution.
Electrodes which are mechanically intact with no broken parts can often be restored to normal performance by one of the following procedures:
- General Cleaning: Soak the electrode in 1:10 dilution of household laundry bleach in a 0.1-0.5% liquid detergent solution in hot water with vigorous stirring for 15 minutes. Place junction under warm, running tap water for 15 seconds. Drain/refill the reference chamber. Soak the electrode in storage solution for at least 10 minutes.
- Salt Deposits: Dissolve the deposit by immersing the electrode in 0.1 M HCl for five minutes, followed by immersion in 0.1M NaOH for five minutes, and thorough rinsing with distilled water.
- Oil/Grease Films: Wash electrode pH bulb in a little detergent and water. Rinse electrode tip with distilled water.
- Clogged Reference Junction: Heat a diluted KCl solution to 60-80oC. Place the reference portion of the pH electrode into the heated KCl solution for approximately 10 minutes. Allow the electrode to cool while immersed in some unheated KCl solution.
- Protein Deposits: Dissolve the deposit by immersing the electrode in a 1% pepsin solution with a background of 0.1M HC1 for five minutes, followed by thorough rinsing with distilled water.
After any of these special cleaning procedures, remember to drain/refill the reference chamber, if refillable. Soak the electrode in storage solution for at least 10 minutes.
If these steps fail to restore normal electrode response, replace the electrode.
CALIBRATING THE pH ELECTRODE
As part of the care for your pH meter, always be sure to calibrate it regularly. This makes your readings more accurate, and may also give you an indication of whether the electrode is damaged or not. Calibration is a pretty simple task, and you should follow the manufacturer’s instructions for your specific machine, but basically you simply need to submerge the probe in a solution of known pH (these can be bought specifically for this purpose) and tell the machine what it should be reading.
Even if you take the best care of your pH meter, it’s vulnerable to the effects of aging. The electrodes aren’t going to work perfectly forever, and there may come a stage where it simply needs replacing. A good sign of an old electrode is a delayed response time while you’re taking your measurements. An older electrode may also need more frequent calibrations, and you’ll need to pay attention to the conditions in which the pH meter is kept: keep it in a cool place, keep the electrode hydrated and avoid any situations in which the electrode could be dropped or damaged.
Posted by Owolabi Abdulakeem