Thanks to Shri jkp sir for quality improvement through kss.
as Dr.kvs murthy garu focused on pH meter.
You want good pH data. Who doesn’t? You
deserve good data, but for good pH data you need to calibrate. You need
to calibrate well and calibrate often. For more precise pH measurement,
you should calibrate before each measurement, but a good rule of thumb to
follow is to calibrate your pH meter at the beginning of each day.
OK, so we know we must calibrate, but for some reason
your pH probe is not calibrating.
There are several things you should check for if
you’re experiencing pH calibration problems.
1. Check the age of the probe.
Probes for your pH meter generally last 12-18
months. This holds true whether the probe is being used or not. The
lot code will determine the age of your pH probe. A lot code is two
numbers than a letter. The numbers indicate the year of manufacture and
the letter indications the month, i.e.-A=January, B=February, C=March
etc. Please note that the letter “I”is not used, this means H=August and
J=September and so on.
Lot code ex:12A*
*probe was manufactured in January’12
2. Perform routine maintenance.
Keeping your pH probe clean can also help eliminate pH
calibration problems. If the reference junction on the probe is not clean
the probe may become unresponsive. Soak your probe with 1:1 bleach water
solution for about 30 minutes regularly to reduce the chances of this
happening. If hard deposits have built up on your probe, you can clean
these by soaking the pH probe in vinegar or 1M (molar) HCL (hydrochloric acid)
for about 3 minutes. pH probes usually require weekly or monthly
cleanings.
Always check your pH meter manual for calibration and
routine maintenance information.
3. Check for physical damage to the probe.
If your probe is damaged, broken glass bulb, crack in
the glass etc., the probe must be replaced.
4. Confirm that the pH probe has never dried out.
Always store your pH probe in a moist environment or
submerged in buffer 4 solution. If you find your pH probe has dried out,
it will have to be replaced.
5. Check the temperature probe used with your
instrument.
Check your probe’s temperature specifications.
pH will not function accurately if the temperature probe is out of
specification.
6. Always use fresh, unused, unexpired pH buffers
for calibration.
You never want to re-use buffers for
calibration. Once buffers are used for calibration, they are assumed
contaminated. Re-using buffers can lead to slow responding pH probe
performance or the inability to calibrate at all. This re-use can also
make it difficult to determine whether the probe or the buffers are causing the
pH calibration failure.
A good way to use re-used buffers is for probe rinsing
only.
7. Perform at least a 2-point calibration-Buffer
7 MUST be one of these two points.
8. Always start with Buffer 7 when calibrating
your instrument even though it is not always required.
9. Reset the calibration to factory default is
possible.
Not all instruments are equipped with this
ability. It is a good idea to consult the user manual. The user
manual will also supply the proper process to do this task because this process
can vary depending on the instrument.
10. Confirm the pH probe response time in each
buffer.
Response time should be no longer than 60
seconds. Response time can depend on the age and cleanliness of your probe.
11. Check the millivolts in each buffer.
- Buffer 7 should be 0+/-50 mV.
- Buffer 4 should be 165 to 180 mV away from the buffer 7 mV value, in the positive direction.
- Buffer 10 should be 165 to 180 mV away from the buffer 7 mV value in the negative direction.
12. NEVER accept out-of-range calibrations.
If you accept an out-of-range calibration, your probe
will not calibrate. It is highly likely you will not collect any usable
pH data if an out-of range calibration is accepted.
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