pH meter

[TishTash]

I purchased the pH meter from TFTestKits.net, and am pleased with its performance so far. A couple of questions for anyone who’s used it:

1) How often does it need to be calibrated in the future? The instructions leave something to be desired: “whenever. [sic] The electrode has been used(laid) for long time.”

2) Do you need the two (or all three?) solutions during recalibration, or is the 7.2 solution from TFTK’s sufficient? Another thread (and TFTK itself) mentioned using just the standard solution, but I’m wondering about the need for a second buffer when initially calibrating. Which brings me to:

3) When using more than one buffer, after adjusting the pH reading and placing it in the second buffer, if the reading is off do you re-trim the probe again? Or is the second buffer just a check? Again, the instructions are (amusingly) vague: “After about one minute, until the buffer solution value corresponding to the measurement temperature is obtained.”

Thanks all!

 

[JoyfulNoise]

I purchased the pH meter from TFTestKits.net, and am pleased with its performance so far. A couple of questions for anyone who’s used it:

1) How often does it need to be calibrated in the future? The instructions leave something to be desired: “whenever. [sic] The electrode has been used(laid) for long time.”

pH meters should be calibrated before every use.

2) Do you need the two (or all three?) solutions during recalibration, or is the 7.2 solution from TFTK’s sufficient? Another thread (and TFTK itself) mentioned using just the standard solution, but I’m wondering about the need for a second buffer when initially calibrating. Which brings me to:

Only very high end pH meters (technical lab grade meters) use multipoint calibration. Most pen style pH meters simply need to be calibrated around the pH value closest to what you expect to measure. So, for your pen meter, you can simply use 7.0 pH standard solution.

3) When using more than one buffer, after adjusting the pH reading and placing it in the second buffer, if the reading is off do you re-trim the probe again? Or is the second buffer just a check? Again, the instructions are (amusingly) vague: “After about one minute, until the buffer solution value corresponding to the measurement temperature is obtained.”

Thanks all!

Unless the meter uses multipoint calibration (yours likely does not), then it should only be calibrated in one buffer solution. Buffers are typically 4.01, 7.0 and 10.01. Use the solution closest to the range you expect to measure in.

 

[TishTash]

Thanks for the reply, JN!

 

[tredos1]

Hey guys, follow up to his question. I bought the same meter and cal'd it with the pH 6.86 powder that came with the meter. I then checked the cal with the pH 4.0 powder that came with the meter and it was way off. Maybe expected for a single point cal, I'm not sure. I then measured my pool water with my test kit and the meter and they didn't match, meter was 8.1 test kit was 7.8. So, I added a little acid, since i was going to anyhow and dropped it to 7.4, which was a little too much, but then I recal'd the pH meter to the test kit at 7.4 yesterday. Today the test kit reads 7.6 and the meter reads 7.8. I'm swishing it around and leaving in the pool for over a minute and there is a good flow where I'm testing, but I've also done a static test in a beaker and gotten the same result. Do I have a bad meter or is all this reasonable? I have some buffer solution coming.
Thanks,

 

[setsailsoon]

If your pen-type meter has 2 point calibration you can still do single point. I use the one closest to my normal pH which in my case (Hanna Phep) is 7.01. I calibrated every time like Matt recommends then after a month I realized it was holding very close so now I calibrate weekly. Still rarely needs calibration. Each brand and price range meter is a little different so I'd calibrate each time 'till you have some experience with it. Last thing you want is pH out of range because you didn't calibrate.

Chris