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pH electrodes [advice requested]

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Michael Gilligan06/08/2021 18:48:16
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I have just acquired a secondhand pH meter, and am interested to understand the design of the electrode: it seems that they have a relatively short working life, and are not inexpensive.

Can anyone advise, please ?

MichaelG.

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Ref. https://www.hannainstruments.co.uk/ph-electrode-ideal-for-field-use.html

Edited By Michael Gilligan on 06/08/2021 18:50:17

Bazyle06/08/2021 19:02:32
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I don't remember the details from my A-level chemistry half a century ago but suspect it is to do with the use of high purity rare elements on the electrodes, perhaps plated on, that dissolve during the measurement which involves an electrochemical reaction. Possibly a less pure version is adequate for home use.

old mart06/08/2021 19:03:49
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No particular help, I recall having to rinse the probe under a jet of de ionised water and store it in water when not in use. Wiki has some info.

**LINK**

Michael Gilligan06/08/2021 19:43:50
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Thanks, both yes

That should get me started.

MichaelG.

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Five minute video, here: https://youtu.be/P1wRXTl2L3I

https://www.endress.com/en/field-instruments-overview/liquid-analysis-product-overview/pH-sensors-transmitters

Edited By Michael Gilligan on 06/08/2021 20:14:28

J Hancock06/08/2021 20:38:08
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If I remember well , the ph sensor must be kept immersed in distilled water when not in use ?

martin perman06/08/2021 20:45:37
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The last fourteen years of my working life I was using portable pH meters daily, yes the probes dont have a long life and yes they are not cheap, as stated they are immersed in distilled water and need washing after use. We used Hanna Instruments Leighton Buzzard.

Martin P

not done it yet06/08/2021 20:46:08
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I’ve had mine about 20 years. Secondhand when I bought it. It’s a Hanna HI 9524. Works well enough.

Michael Gilligan06/08/2021 21:08:42
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15643dbe-5cd6-46d3-9134-5dbeab93e238.jpeg

Nick Clarke 307/08/2021 07:53:29
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Amazon list them starting under 10 quid - interestingly exactly the same advert with the same picture but a different brand name is £25!

Paul Lousick07/08/2021 08:14:32
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Lots of inexpensive ph meters on ebay, advertised for testing swimming pool water. Also used for testing boiler water instead of using litmus paper to determe amount of treatment required.

not done it yet07/08/2021 08:52:31
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Posted by Paul Lousick on 07/08/2021 08:14:32:

Lots of inexpensive ph meters on ebay, advertised for testing swimming pool water. Also used for testing boiler water instead of using litmus paper to determe amount of treatment required.

Litmus paper? Only really good for seeing if acidic or alkaline. There are several narrow range pH papers available. I had several books of papers, but I expect they have got lost since buying the meter (cost me less than a fiver, I expect).

It does get used more often for temperature measurement these days - but I did get it out just this last week to measure the pH of a couple of things - to sort out which was which. I’m now wondering where my buffer solution concentrates are hiding…

It was my regular task, at school, to test the pool water each morning - it got me away from the morning assembly (which my form master knew I would avoid, if possible).🙂

Thor 🇳🇴07/08/2021 11:09:12
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The pH meters I used years ago had a glassbulb electrode that was stored in potassiumchloride solution after use (and cleaning).

Thor

Neil Wyatt07/08/2021 20:10:26
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Ditto.

I recall ones with porous glass electrodes and all manner of fuss to keep them accurate.

These days I have a large bottle of universal indicator, I've used it very rarely over 20 years, but it's invaluable if you do need it.

Neil

Barry Smith 403/09/2021 23:43:51
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Hi, I've been a water chemist for more than 40 years. You need to store the electrode in KCl solution and if dead they can be revived with 2m HCl. Ideally don't store them in distilled water. I think it's 2m KCl but will check. You calibrate the meter using buffer solutions at pH 4 and 9 or 4 and 7. These can be purchased cheap off ebay. They are called buffer solutions because they are designed to resist pH change and hence allow an accurate calibration. Between measurements wash the bulb with distilled water and wipe with a tissue. The bulbs are made of thin glass and easy to break, then you need to replace them. Like most things the more you pay the better the electrode.

Typically only accurate between pH 3 and 10. They are a combination of a silver/silver chloride reference electrode and a glass membrane electrode.

The voltage produced between the reference electrode and the glass bulb is proportional to the log10 of the hydrogen ion concentration acording to the nernst equation. Hope this helps

Barry

Michael Gilligan04/09/2021 00:03:53
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Thanks, Barry … much appreciated

MichaelG.

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