pH meters

[J]

I have a question regarding pH meters. We have several, including the sensors for data loggers, and none of them give us even close to accurate readings. We have a small amount of money to spend, so would like to hear about any that can be relied upon.
Thanks in advance
J

[Jazz]

I bought mine from J car Electronics, paid $49 on special; you can negotiate price, use plain 9V battery; comes in hard case with pH 7 buffer included

[RosalieM]

Julie,
have you tried calibrating them? I've had to re-calibrate 3 or 4 times in a row before they are accurate sometimes. I've started using the buffer tablets you can get from serrata to make up the calibration solutions and then dispose of them at the end. It can be very time consuming to do the calibrations though.
Rosalie

[J]

I remember trying ages ago to calibrate them, with no success. Perhaps I should persevere.
Thanks Rosalie and Jazz

[Ocker]

I was going to say the same thing
You have to calibrate them
Datalogger type have procedure
Others you put in 7 buffer, set zero to & then put in 3 or 10 buffer and adjust span screw till right then repeat zero value will have changed slightly re zero (7) then tweck span then check again.
Some take 3 or 4 goes to get spot on

[nickyw]

I purchased 2 pen type pH meters from wiltronics $55.00. They are great they are little and can be taken out in the field without having to take the whole data logger etc. Very reliable although the cherubs broke the electrode in the first week but you can buy a replacement for $35.00. Too easy

[merilyn]

pH meters should be calibrated each day they are used. You have to be super careful with the bulb, it is easily damaged by the oil off your skin, so no one is to touch the bulb at all. But try telling that to a bunch of teenagers!
The one from Wiltronics is a bargain if you can get replacement bulbs so cheaply - wish I'd seen those about a month ago (when I ordered somewhat dearer ones).

[MariaC]

Not all pH meters require calibrtion everytime they are used, many esp those for data loggers are best left alone and many of the newer ones come factory set. If you do have to calibrate, do over a range eg pH 4, 7 & 10 and you can check periodically or before they are used that they are correct by testing in a buffer of known pH and checking the reading. In my exp the most important thing with pH probes is to store them correctly. If they are in a storage solution make sure the probe is kept upright in the solution. I have mine standing up in an old test tube rack. Also check the instructions for each probe, some are rinsed with distilled water, others with tap, this can affect performance and the life of the probe. Cheers MariaC

[Robb]

Hi All,
Do a seach of the topics in Chemtalk . Once I had posted a pH electrode ReJuvenation process which is very effective for the stubborn pH meters that don't give accurate readings.
pH meters rely on transfering current across the ISE (Ion Selective Electrode), (Glass Bulb on the end) so really they don't get shot unless wires break inside them.

As long as the Glass Bulb is free of any film build-up just like glass that is dirty with grease, they will perform as they should.

One thing though to check, would be to see if the electrolyte solution is still present in the INNER tube of the electrode. This is another reason for inaccurate results.

Before you throw any away though, simply search for my previous post a few years back and you will find the instructions there. Also there is an ingredient list for making pH soaking soluiton as well to keep the ISE's from drying and keeps them protected from glass bulb freeze..

Hopoe this helps,

Cheers,

Robb.....

[J]

Thank you all. I'll check out your rejuvenation process first, Rob, and see how I go.
Putting the whole thing on hold though for now, as I'm taking a couple of weeks LSL.
Heading off on sunday for a roadtrip to...? We haven't decided yet, we'll make it up as we go along.
Can't wait!!
J

[Robb]

Enjoy it, and have a safe on at that!

Cheers,

Robb.....

[Robb]

Hi All,

Here is the found pH rejuvenation technique in its original state.....

Hi All,

While we are on the electrode topic, I would like to offer a rejuvenation technique that can be safely performed on the electrode. This enhances sensitivity that has been lost due to the following:
Long storage periods without immersion in a pH Electrode solution;
The electrode has been exposed to the air too long (for months);
The electrode has been exposed to damaging solutions;
The electrode/s have lost it’s/their speedy response times.

To rejuvenate an electrode simply immerse it in 10M (32%) or 12M (36%) Hydrochloric Acid for 1 minute (no longer) then put this straight into a solution pre made to pH 7.00 without rinsing the electrode at all. (discard the ph 7.00 solution after use as the ph will have changed due to the electrode being first immersed in Conc HCl).

Keep the electrode in this solution for approx 5 mins and then remove and rinse with distilled water. Store the electrode permanently in a pH Soaking Solution until it is ready for use, then rinse and immerse in the solution to be tested and the sensitivity and quick, stable accurate response will have returned.

I hope this has rejuvenated some of those old and dusty pH electrodes.

Robb.....