Sciencemadness Discussion Board

Glass for homemade pH electrode

Cesium Fluoride - 3-2-2010 at 21:36

Hi everyone,

I searched a little bit but couldn't find anything on this topic. I was throwing around the idea of building a pH meter for fun. I can easily get all the components needed except the glass electrode. It is my understanding that these things are about as thin as possible and still have resistances of 100-1000 megaohms. I was wondering if anyone knows of some household glass item that could substitute as a glass membrane in an electrode. Otherwise, I suppose I could learn how to glass blow.

Thanks.

Alexein - 4-2-2010 at 09:25

i heard it's a really special glass, not something we can get off the shelf or in a household item.

But a pH probe for aquarium monitoring can be had off ebay for $20. So making it yourself i think is more trouble than it's worth.

the accuracy is crappy though in that it's 1 pH unit off.

Electronics should be straightforward, i think all you need is a really good instrumentation amplifier with extremely low input bias current.

12AX7 - 4-2-2010 at 10:39

I thought it was sintered glass (i.e. microporous).

Tim

Alexein - 4-2-2010 at 13:22

Interesting, if that works go for it :)

densest - 4-2-2010 at 13:46

US Patent 4297193 - pH Electrode glass compositions has some useful (?) information about glass for pH electrodes. It's not something for amateurs. Li (a lot) Nb or Ta (some) La, Pr, etc (a little) U (maybe), Rb or Cs (some), with assortments of others to taste.... I haven't seen any theory of why to use which elements.

A straight lithium glass would probably work but badly. The thickness should be in the area of 1 micron which makes severe demands on the strength of the glass. My guess is that it would be a matter of blowing 20 or 30 bubbles on the end of a lithium glass tube as thin as possible, then selecting the one(s) that didn't break. Yet. Corningware (tm) is reputed to be a high lithium glass. One might make a gather of it on a pyrex tube, draw it out as a tube, then blow a bubble on the end. I assume it would have to be annealed or it would shatter at the transition from thin to thick.

@12AX7 - the sintered glass is to make an ionic connection from the internal solution of the electrode to the specimen under testing with as little cross-contamination as possible. It's not the ball/tube/bubble at the end of the electrode, it's further towards the handle in a ring to complete the circuit.

Any significant sodium content in the glass would probably make it (1) dissolve in alkali (2) wildly fluctuate in potential or (3) shatter.

I continue to be amazed at what Google will show you and what the various patent offices have for information... though one should be sceptical of claims in a patent & Google just reports what people have babbled electronically....


[Edited on 4-2-2010 by densest]

[Edited on 4-2-2010 by densest]

dann2 - 4-2-2010 at 15:03

Hlelo,


Perhaps this may be useful if you request it in the reference section. The glass is 'replacable'. Does this mean you can purchase it as a common type of glass? Cannot read far enough to find out........

http://www.springerlink.com/content/u3711j3440020471/

here too
http://www.horiba.com/process-environmental/features/water-q...

Get yourself some fuzed quartz (old bar type 500w light tube) and some Litium Carbonate (yum yum) from the ceramics store and an oxy-acetylene cutting torch and make some Li glass and blow yourself a bubble or even use a flat piece in a cell type effort.



Dann2

watson.fawkes - 4-2-2010 at 17:11

Quote: Originally posted by densest  
US Patent 4297193 - pH Electrode glass compositions has some useful (?) information about glass for pH electrodes. It's not something for amateurs. Li (a lot) Nb or Ta (some) La, Pr, etc (a little) U (maybe), Rb or Cs (some), with assortments of others to taste.... I haven't seen any theory of why to use which elements.
I haven't read anything definitive on the subject, but it's my understanding that these are all there to improve the conductivity of the glass, both electronic and ionic. For electronic conduction, most of the elements you mention have relatively heavy nuclei, whose outer electrons have relatively weak binding energies. I would guess that their unoccupied d and f orbitals are available for conduction (think LUMO applied to conduction rather than bonding). For ionic conduction, I get the impression that Li somehow makes the glass matrix more porous to proton conduction, likely by reducing the collision cross-section density. I'm tentative about these claims, but I hope they provide a starting point.

Cesium Fluoride - 6-2-2010 at 12:18

Thanks for the information all. I guess I'll try blowing some thin glass and when I get around to it, I'll post something here. The circuitry is simple and not something I'm worried about. I already have a cheap commercial pH meter so this is just a project purely for the fun of it.

chief - 6-2-2010 at 13:00

Why not try to start from sodium silicate ("water-glass"), make it to a gel, then heat it, maybe glow it
==> Should give some micro-porous glasslike stuff ...

maybe not as durable as commercial-grade electrodes ...

The easily obtainable sodium silicate is usually made by fusing quartz with NaOH ...
==> Maybe a Li-Variant could be made by fusing with LiOH instead ?

[Edited on 6-2-2010 by chief]

entropy51 - 6-2-2010 at 14:02

I think the Amateur Scientist column in Scientific American described a DIY pH meter back in the day. I don't recall anything about the electrode, but if someone has the Amateur Scientist on CD-ROM, it might be worth looking at.

Edit: I found a paper copy of the article. It does describe two different home-made pH electrodes.

[Edited on 6-2-2010 by entropy51]

jimwig - 7-2-2010 at 11:49

check Journal of Chemical Education

edit - quick check shows 121 articles with "electrode" in the title

[Edited on 7-2-2010 by jimwig]

Small-Scale and Low-Cost Electrodes
for “Standard” Reduction Potential Measurements
This article describes how to construct three simple and
inexpensive electrodes: a hydrogen, a chlorine, and a copper
electrode.
April 2007 Journal of Chemical Education


[Edited on 7-2-2010 by jimwig]

low tech electrodes

protem - 8-2-2010 at 00:02



Small-Scale and Low-Cost Electrodes
for “Standard” Reduction Potential Measurements

Per-Odd Eggen and Lise Kvittingen*
Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway;
*Lise.Kvittingen@nt.ntnu.no
Truls Grønneberg
Department of Chemistry, University of Oslo, 0315 Oslo, Norway

Attachment: electrodes.pdf (131kB)
This file has been downloaded 1453 times

Flamethrowa - 16-3-2010 at 11:35

I think the funky combination of ions in the glass has something to do with specificity too - the potential is basically the result of ion exchange at the surface of the glass, and using a high sodium glass will make the probe respond to sodium ions at higher activities. Perhaps the softer, lower metal ions don't exchange so readily/are very rare in most things you'd measure?

halogenstruck - 2-4-2010 at 16:34

i tried it before by many different formulations.
the problem was this.as you must use regular glass tube and PH sensitive bulb is different glass,their expansion constant are different and when cool down,it cracks
but the last formulation i applied which gave positive result was a mixture of:
Li2CO3+CsNO3+La(NO3)3,xH2O+SiO2 then i added extra nitric acid and them melting with a torch in graphite crucible

also attached PDF file, electrodes.pdf , is corrupted

[Edited on 3-4-2010 by halogenstruck]

halogenstruck - 2-4-2010 at 17:35

i downloaded many times but did not opened.
but now it opened!thanks
i read article,it`s about hydrogen electrode.for PH meter,you need glass electrode.
i read before that article writer used a noel bulb as glass electrode and it worked

[Edited on 3-4-2010 by halogenstruck]

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