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unionised
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My 1963 copy of the British pharmacopoea gives details of testing glass vessels for alkalinity by extracting with hot water for half an hour then
measuring the base colourimetricly. The limit for acceptability is equivalent to extracting about 0.2 mg of NaOH. Since the containers they are
concerned with are about 10 ml in volume that's about 20ppm.
"Detectable, but insignificant outside of rinsing in-process silicon wafers..or something."
Detectable by the colour change of an indicator (hardly the most obscure test) and enough to destroy base sensitive drugs (that's why the BP is
interested).
I agree that the water stored in a glass bottle will almost certainly be pure enough for most things but a plastic milk bottle will often do better.
The nuclear industry uses tons of D2O for things and, for a lot of those things, they recirculate it through a purifier. They do that precisely
because they know that water doesn't stay pure for long.
That could explain why they can tolerate levels of contamination that would be unacceptable for pharmacology. It's also fair to say that, for NMR the
presence of disolved Na compounds won't usually make a difference. For HPLC/MS the sodium adducts are sometimes a royal pain in the neck- even using
lab grade (borosilicate) glassware and methanol or acetonitrile as the solvent.
"We have to stop and think about what is significant and what is not. "
OK, let's do that.
The isotopic purity of a deuterated solvent is no measure of the presence of ionic impurities. Also, we weren't talking about other solvents, just
water.
The cheap polyethylene barrels used for D2O are not going to leach alkalies into the water. That makes no possible difference to whether or not
Prole's glass jar will.
The plastic jugs in which water is sold are usually clear plastic (so people can see the water is clear I guess) therefore they are not made from
polythene which is slightly cloudy.
They may well be made from polyester or polycarbonate. That's a fairly reasonable source of of the chemicals I mentioned.
And, you don't know the difference between restistance and resistivity.
While we are at it, I have seen crystals (and quite good ones too) of sugar an inch or so across. They took years to grow
If you don't like sugar as a molecule, I'm sure we have all seen gemstones which are molecular solids (There's no way diamond is ionic).
If you really want nice crystals, ask the semiconductor industry- they grow silicon to huge sizes in single crystals
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jack-sparrow
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| Quote: | Originally posted by unionised
The isotopic purity of a deuterated solvent is no measure of the presence of ionic impurities. Also, we weren't talking about other solvents, just
water. The cheap polyethylene barrels used for D2O are not going to leach alkalies into the water. That makes no possible difference to whether or not
Prole's glass jar will. The plastic jugs in which water is sold are usually clear plastic (so people can see the water is clear I guess) therefore
they are not made from polythene which is slightly cloudy. |
If you have significant monomer/polymer leeching in 99.96%D D2O you will see it in NMR. At this enrichment level, you can see contamination level at
the ppm level. I have no problem storing 100 000 $ worth of heavy water in a plastic barrel. Our quality standard is that no impurity is visible in
the base line when the spectrum is normalized on the C13 satellites of the main solvent peak (this is ppm level). Obviously in D2O you dont have C13
satellites but you need a flat baseline anyway and D2O is always the most enriched solvent we have because all others are derived from D2O. When I
spend 50 hours on purifying NMR solvents to remove the last impurities, I want to keep it that way and glass jugs for organic solvents and plastic
jugs for water are enough for my purpose. Sorry I don't deal with semi-conductor grade crystals or USP grade pharmeceuticals but you are right, in
these case water purity might be a major issue.
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prole
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Hmmmm, ah yes, perhaps 'molecule' was a poor choice of words. Sorry. I forget that I'm not talking to my ape-ish coworkers, but very knowledgable
folks. Ionic substances are easier to grow as crystals, but, most any crystalline substance may be grown given ample time and proper conditions.
Given the fact that I just read a whole book about synthetic diamonds...
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lordmagnus
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Distiled water purity
Well, just as a test, I distille dthe last liter of a gallon of R.O. water I had in the fridge. I ran it with a 2000ml boiling flask connected to a
liebig condensor, I don't have a conductivity meter, but when the boiling water reach about 100ml, I took a good look at it, and it appeared clean. It
is possible that if you were using R.O. water like I was, the plant that made it might have had a torn membrane or something like that, which caused
the contamination.
I\'ll kill a man in a fair fight, or if I think he is gonna start a fair fight, or if he\'s bothrn me allot, or if I am getin payed good, or probably
over a good woman.
-Jayne Cobb (Serenity) |
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prole
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Lordmagnus,
The water I used was 'steam distilled' (from the label), and I distilled 4.0-ish litres of it. I didn't remove the distilling flask from the oil bath
to check it until I was finished with the project, but peering into it periodically revealed that it was probably clean until the 3rd litre was run
through.
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lordmagnus
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On the subject of water purity, check E-BAY, you can get a T.D.S. (Total Dissolved Solids) meter for 20$ or so, it measure the resistance across a
couple of platinum electrodes in the tip of the pen style meters, the higher the resistance, the purer the water. Distilled water should be the
purest, you can get pretty close with R.O. water, as long as after the R.O. element, it doesn't pass through any other filters, carbon after the R.O.
would degrade the purity a little, and really wouldn't make any since, since they usuall use 2 or 3 .5 micron carbon filters before the r.o. membrane
to keep the membrane clean and long lasting.
I\'ll kill a man in a fair fight, or if I think he is gonna start a fair fight, or if he\'s bothrn me allot, or if I am getin payed good, or probably
over a good woman.
-Jayne Cobb (Serenity) |
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