As I said before,
Autotitration with a pH/potentiometer will give you best results. It allows
the laboratory technician or chemist to see shifts in the titration curve,
as it is usually plotted by such systems. It will help you determine when to
change the bath. since endpoint can be determined for almost every alkali in
the solution, it can help you, no guaranty but it usually does, determine
contaminants simultaneously as you determine the saponifier.

For additions by the operators during the day, due to drag-out or similar
circumstances a drop test kit is usually more then sufficient.

If you want proper control you have to use the proper tools.
Both of the above testing techniques beat the hell out of the Brix as Rudy
said.


Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]


-----Original Message-----
From: Brian Ellis
Subject: Re: [TN] Saponifier concentration measurement

I agree mostly with what the others say, but only up to a point. Saponifier
solutions consist essentially of four components: water, an alkali (usually
monoethanolamine or a near relative) and a water-soluble solvent mixture,
such as glycols/diglycol ethers, etc., and a buffer. As the alkali is used
up for saponifying
the carboxylic acids in the residues, so the quantity is diminished, but the
pH hardly changes, because the solution is buffered to prevent attack of
amphoteric metals. pH, as such, is therefore useless for determining the
amount of MEA available. Titration will give a relative value, in the form
of a straight-line
curve but the zero is not at the origin of the axes, also because of the
buffering. However, it should not be forgotten that some of the
saponification reaction products are also basic, which may make you think
you have more saponifier than is really present. This means that absolute
values are hairy. The function of
the solvent mixture is to dissolve soluble contaminants and to lower the
surface tension. The amount of these present is not easy to determine on the
workshop floor and the ratio of MEA:solvents will inevitably drift away from
the optimum and even the solvent mixture itself will alter with differential
evaporation and
bonding to contaminants. Replenishing saponifier baths is therefore fraught
with the hazard that, sooner or later, things are going to get out of
control.

The mechanics of titration are simple and easy but I suggest that you use a
colour indicator with an end point of between 8,5 and 9.  Phenolphthalein is
frequently used, with a range of about 8,2 - 10. A better one would be
ethyl-bis(2,4-dimethylphenyl)acetate with a narrower range of 8,4 - 9,5. If
you use a pH meter
for the work, then choose 8,7 as your end point. This will reduce (but not
eliminate) errors due to the presence of basic saponified residues.

You could fully automate the titration and the addition of fresh concentrate
to maintain the acid acceptance at a constant. This would not be
horrifically expensive (a few thousand).

However, all this is a little theoretical, because no amount of simple tests
will determine the cleanability of your saponifier solution with your
particular flux residues. The simple answer is to try to change the solution
just before it starts to give poor cleaning results. How? I don't really
know, because there are
simply too many uncontrollable parameters.

By the way, there is an excellent book which concentrates on saponifier
cleaning. One of the co-authors is Frank Cala who is very active on IPC
committees, the other being an ex-colleague of his, Tony Winston. It is
entitled "Handbook of Aqueous Cleaning Technology for Electronic
Assemblies". There is also a chapter on
the subject in my "Cleaning and Contamination of Electronics Components and
Assemblies". Both are from Electrochemical Publications. (Sorry for the
plug!)

Brian

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

Lou, titration beats hell out of degrees Brix, or other convoluted
methodology, however titration is far from the best, and frankly, may not be
a good idea, as it gives a false sense of comfort and security.

The problem with titration is that it measures quantity of TOTAL alkalinity,
and measures impurities, and garbage picked up in the cleaning process, as
ACTIVE cleaner--WRONG!

The perfect example of this is that an old bath that titrates as being fully
up to strength, cleans NOT NEARLY as well as a new cleaner bath.

Much much better, much more indicative, yet not perfect, is to measure pH.
pH tells what sort of alkali is present.  This will not tell you how much
soil you have dissolved/dispersed in the cleaner/saponifier, but is a much
truer indicator of cleaning strength.

The problem with pH is that it does not tell you how much saponifier to add
to bring the system up to the desired pH.  You have to fool around, and
check
it out in the lab, then do the job in production.

Hope this helps, this is not a straight forward subject, and frankly, many
of
the vendors do not understand their own chemistry well enough to be of much
help.

Regards,

Rudy Sedlak
RD Chemical Company

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