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pH measurment question? - (Nov/12/2007 )

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QUOTE (mdfenko @ Mar 21 2008, 04:03 PM)
QUOTE (Astilius @ Mar 20 2008, 11:57 AM)
Cheers, mdfenko. What I should have said is that I was under the impression that aside from the entry point for electrode buffer I thought that there was commonly a smaller hole up at the top of the probe to allow the free flow through the porous plug (and make it easier to fill the probe with electrode buffer). In fact, everytime I've had a new probe I've checked and there always has been.

I've used these things for nigh on 25 years and this has been the case up til now, now I find a probe where it isn't the case...weird.

It makes obvious sense that there should be a hole but...well, it's just weird that this has never been an issue until now.

I don't know what to make of that at all.

i thought it was a little strange that you asked that question. now i understand what you were asking.

my experience is just the opposite of yours. in more than 35 years of lab work i have never seen a pH electrode (combined or separate) with an opening other than the pluggable fill hole (although i have seen a few different ways of closing up the hole).

if there was another hole then the fill solution would evaporate faster and would lead to a lot more crystal formation in the electrode.

Yeah, if there was another hole and you left the fill hole unstoppered you'd run into trouble (or more liable to).
I'm sure the advice I always followed was only plug the wee hole (along with the fill hole) if you're transporting or storing the proble for a long period of time.

I'd love to say that maybe suppliers have moved away from the other smaller hole as if you don't unplug it initially then you can experience measurement issues and it's more difficult to plug later too (I just used Parafilm) [or maybe because the smaller holes are liable to crystalization]...but, well, you clearly have longer lab experience than me by a sizable chunk so that can't be it.

I'm a bit thrown by this (as you might tell). I really should have checked the Jenway probe right off the bat to see if the smaller hole had been uncovered when it was unpacked (but, as you can guess, there is no such hole).
I feel like an undergrad again. In a bad way. Still, it's a nasty reminder to keep your eyes pealed in the lab as things can change or go against your expectations if you don't keep the basic principles in mind. Bloody embarassing, though.


Your colleague is wrong...


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