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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Tue, 23 May 2006 11:00:30 +0300
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As ex-manufacturer of the Contaminometer, please permit me to add some 
thoughts. As the name implies, ion-exchange resins exchange, er, ions. 
Imagine you have some NaCl in your solution, the Na+ ion is "captured" 
and replaced by an H+ ion. The Cl- anion is replaced by an OH- ion. As 
they are of opposite electrical charges, If H+ shakes hands with OH-, 
they get married, their charges cancel out and you get a molecule of 
H2O, so your salt molecule becomes replaced by a water molecule. After a 
few minutes of passing your solution through the column, nearly alll the 
ionic contaminants are captured and replaced by water.

I have done a bit of research to find the ideal resin for this job. I 
hit on the Rohm & Haas Amberlite MB-1 but not just any MB-1. New resins 
do not work well. My supplier was the Swiss importer and regenerator. 
Regeneration was done in batches, firstly by separation of the cationic 
and anionic resins gravimetrically, treating and rinsing each, removing 
any broken beads, mixing the two types back again in the right 
proportions. Each batch is then thoroughly tested for 1. mass of salt 
which it will exchange, 2. conductivity of water it will produce and 3. 
rate of exchange. Whenever he got an exceptionally good batch, he put a 
drum of it to one side especially for my company. When we bought a drum 
(about 4 x per year), we tested it as well, especially for the 
conductivity of a 50% IPA/water mix; our internal spec was that it had 
to reach 0.005 µS-cm from 1 µS-cm within 3 minutes in a given 
Contaminometer model (we used an old CM-1A for the test). From 1978 to 
1991, when we ceded the brand, we rejected only one batch. New resins 
got nowhere near that value.

Now, here is something that may surprise the unitiated: if you fill a 
column with resins, as received, and then pass an IPA/water solution 
through them, three things will happen: 1. the solution will turn 
cloudy; 2. the solution will drastically change proportions; 3. about ¼ 
of your resins will apparently disappear. I don't know the why of the 
cloudiness but I do know it disappears after a few minutes of 
regeneration, leaving no residue in the solution, so I wasn't bothered. 
The change in proportions of the solution is obvious; as supplied, it 
contains an enormous volume of water, and this is exchanged for the 
solution within the resin beads. The apparent disappearance of resins is 
for the same reason: if you take 1 l of IPA and 1 l of water, you do not 
get 2 l of mixture, you get a lot less. So the volume of resins 
diminishes as they are subjected to the mixture. For these reasons, we 
always preconditioned the resins we sold with an IPA/water solution, 
whether in columns or in replacement packages.

Now for the crunch. You have used a column for 6 or 18 months. It is no 
longer good enough (some of our models' computers warned users when the 
rate of regeneration was becoming too slow). What is in those resins? 
All the ions that have been removed from your test boards: lead, copper, 
nickel, silver, tin, perhaps even cyanides or other nasty organic anions 
(this is why they sometimes took on a greenish cast when there was a lot 
of copper in them). Yes, those resins have turned from a benign, 
non-toxic material into a HazMat and must be treated accordingly. We 
warned users never to dump used resins. We encouraged users to return 
them to us for correct disposal and some did. Whenever we got a drum 
full of used resins, we returned them to the regenerators who treated 
them accordingly. Because they required special treatment, we were never 
credited with the value of the resins, as would have been the case if 
they had been used for deionising water, but we didn't pay, either. So, 
do remember used resins are toxic and hazardous.

And the reason they do not remove the IPA is that it is a polar solvent 
but is much less ionic than even 0.056 µS-cm water, therefore there are 
no ions in it to exchange.

I hope this answers your questions.

Brian

Kevin Glidden wrote:
> Can anyone tell me what is in the cartridges of the ionic testers that
> removes contaminants?  Why does it not also remove the alcohol and just make
> plain DI?
> 
> 
> Kevin Glidden
> Manufacturing Engineer
> Luminescent Systems Inc.
> 4 Lucent Drive
> Lebanon, NH 03766-1439
> Tel # (603) 643-7766 ext. 3152
> Fax # (603) 643-5947
> 
> 
> 
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