Little_Ghost_again
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pH buffer solutions for probes
Hi
I have a pH probe, it came with a bottle that the end of the probe sits in when not in use, any idea what chemical is best to use for this? it isnt
dry yet but I want to use fresh solution.
The other things is what are the best solutions to use to calibrate the probe? its for use in my fermenter mostly but other applications as well.
thanks
LG
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gdflp
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Generally it is a ~4M aqueous KCl solution to prevent the probe from drying out. To calibrate the probe, try searching "pH calibration solution"
there are many different cheap solutions available.
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macckone
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Potassium hydrogen phthalate solution and deionized water are two reliable standards. Most inexpensive probes only have one calibration point. More
expensive ones can have two or three. Potassium hydrogen phthalate solution is also used as storage solution for some probes.
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Little_Ghost_again
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Thanks, I am pretty sure its a decent probe, I got it as a freebie in a philip harris fementer kit.
I wasnt surewhat the solution was that the probe is kept in. I will have a look on ebay for some calibration fluid, i was curious as to what they use
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unionised
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As calibration solutions you can use saturated solutions of borax pH 9.32 ) and cream of tartar (pH 3.567)
http://pubs.acs.org/doi/abs/10.1021/ac60010a017
http://www.borax.com/docs/product_pdfs_data/pds-borates-bora...
both are easy to get and cheap.
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blogfast25
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I keep mine in deionised water. Seems to work fine. If you don't use the probe often you'll need to calibrate it each time before use.
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macckone
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Some probes are ruined by deionized water. Without knowing the exact probe, picking a storage solution is difficult.
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Little_Ghost_again
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I have those on hand so will give it a go
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Little_Ghost_again
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I just assumed probes were pretty much the same! all I know is it came with a philip harris fermenter kit and has a glass bulb on the end and the
probe has a liquid inside it, I also have a JBL pH probe for my fish tank, its part of a co2 system for my planted fish tank, But I dont use it now as
I foundthey grow better with the co2 from ethanol production!
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blogfast25
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If by 'probes' we mean combination glass electrodes specifically for pH measurement, then yes, they are all pretty much the same. Deionised water or
dilute KCl should work just for storage.
Those pen type pH probes most people use all come with DIW as recommended storage liquid, AFAIK.
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macckone
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Hanna instruments recommends pH 4 solution for storage. This is potassium hydrogen phthalate solution. In there care instructions they say in big
bold letters and all caps DO NO STORE YOUR PROBE IN DISTILLED WATER.
Fischer scientific has the same recommendations. They also describe the various types, gel filled, calomel, silver chloride and solid state. They
use italics and say never store an electrode in distilled or deionized water.
Cole Palmer recommends 4M KCl solution for storage and also states partially in caps DO NOT store electrode in distilled or deionized water.
MRC lab recommends pH 4 with KCl and sodium generate but does not recommend against distilled water.
In short different manufacturers recommend different storage conditions. I am sure some may even recommend distilled water but a number indicate that
is bad.
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blogfast25
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"sodium generate"?
Both my pen types recommended DIW. Both still function well after years of often abuse, frankly speaking.
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MrHomeScientist
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You could always test the solution! Silver nitrate to test for chloride and flame test for potassium color. In my limited experience with probes,
they've always had KCl as the solution.
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macckone
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Quote: Originally posted by blogfast25  | "sodium generate"?
Both my pen types recommended DIW. Both still function well after years of often abuse, frankly speaking. |
That should be sodium benzoate. My post was attacked by spell correct on my tablet.
If they recommend deionized water, that is what should be used, but if they say DO NOT use it in bold or italics it is probably best not to use it.
My point is that different probes recommend different solutions. Most (but not all) pen type probes are gel type or FET type and what little ghost has
is probably silver-chloride. Unless it is fairly old, a calomel probe would have a mercury warning. My guess is that it requires either pH 4 or KCl
storage solution. With KCl being a safe bet.
Testing the remaining storage solution is one good way of determining if it is potassium hydrogen phthalate or KCl or DIW. If the pH is 4 then it is
the potassium hydrogen phthalate buffer, if it precipitates silver chloride with silver nitrate then it is KCl assuming the pH is close to 7,
otherwise it is likely DIW.
As far as I know all storage solutions are pretty much one of those. Although as MRC states their solution contains KCl and sodium benzoate as
additives. I assume other solutions my have additives to prevent bacteria growth as well.
Additional note, if it came with a sponge type storage case then you would add deionized or distilled water because the KCl or pH 4 buffer doesn't
evaporate. This is not the same as storing it in DIW.
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aga
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"Spell Correct" has never worked properly, and caused of the demise of the modern Witch (or Warlock).
Nothing goes worse than a Spell that should to change a Toad into a Prince and ends up making a Traffic Warden.
Lacks the p'zazz.
I blame it all on the Tablet Kings, aka Glaxo.
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macckone
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Sodium benzoate being replaced by sodium generate could be pretty bad too when you add water.
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Little_Ghost_again
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The solution it sits in is a kind of dark grey almost black. the solution actually inside the probe is clear, there was a Hanna probe here but its
been with out any storage solution fr a very long time.
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