Learnaboutgmp Community

pH meter calibration

We currently calibrate the pH meters on each day of use. However, some think we should do more than once throughout the day. We measure the drift throughout day and try to get info from USP on acceptable amount of drift - USP no help, help. What is common practice at other labs? We be GMP lab in the pharma company.

Dear Mojo,

This is a good practice that pH meter must be calibrated at three points from acidic to alkaline via neutral, the frequency of calibration I recommend that it should be calibrated/ verify at the start of day working, whenever pH meter on, if you observe out of trend results, or pH electrode found sticking some material.
All the calibration time, the drift must be logged in the log book.

Regards,

[quote=Shahnawaz]Dear Mojo,

This is a good practice that pH meter must be calibrated at three points from acidic to alkaline via neutral, …

[/quote]

please check the pH range for electrode first to choose appropriate points for calibration.

First Calibrate with Ph 7.0 (Neutral Buffer)
Clean and Calibrate with 4.01(Acidic buffer).
Clean and Calibrate with 10.0(Alkaline Buffer)

Buffer solutions above ph 7.0 are less stable.So always make them fresh.

3 point calibration is always good.
Some microprocessor Ph meters can be used with 2 point calibration to determine the Slope.You must refer the specification and ph range of your electrode (as said by SYX).

Regards

[quote=DURGA PRASAD]First Calibrate with Ph 7.0 (Neutral Buffer)
Clean and Calibrate with 4.01(Acidic buffer).
Clean and Calibrate with 10.0(Alkaline Buffer)

Buffer solutions above ph 7.0 are less stable.So always make them fresh.

3 point calibration is always good.
Some microprocessor Ph meters can be used with 2 point calibration to determine the Slope.You must refer the specification and ph range of your electrode (as said by SYX).

Regards[/quote]

For linear result (straight line) calibration should be done on three points, Two points calibration is not recommended.

dear all

in our lab, we do the calibration at least 3 points, but there is a situation, sometimes the pH used in method may out of the calibration range (like 4-7-9.21, used pH is 10.1)
than we will recalibration as a range 7-9.21-11.01.
as our observation, if we calculate the pH out of the calibration range, will make a significant deviation.

Thats a good point by PAT.
These days we are getting standard buffer tablets around 10.5 Ph.
We have to make that buffer as per specification with Distilled water and then bring these PH meters around the range you were reffering.
Then you can be rest assured that the pH you are mesauring will be near accurate.
above 10.5 is always near accurate.
Its rather difficult range we are asking the pH meter to perform.

Regards

[quote=Shahnawaz]Dear Mojo,

This is a good practice that pH meter must be calibrated at three points from acidic to alkaline via neutral, the frequency of calibration I recommend that it should be calibrated/ verify at the start of day working, whenever pH meter on, if you observe out of trend results, or pH electrode found sticking some material.
All the calibration time, the drift must be logged in the log book.

Regards,[/quote]

Hi
Is it advicable to use pH meter, which has been calibrated at the start of the day, after mid night(That’s next day offically) on extended working hours, Please sujest me…

Pharmacopeia provide clear guidance on how to perform calibrations. The original post is seeking guidance on calibration frequency. Daily calibrations is commonly used in the industry but I’ve seen organizations where calibrations are valid for up to 4-hours only.

If I were to determine a drift limit to determine the calibration frequency requirements under actual conditions of use, I would not allow drifting in excess of the USP calibration requirement of ± 0.05 pH units.

Perform verification before each test I don’t. Calibrate on a known frequency and the verification, performed before each test, will satisfy any regulatory requirements