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PLASMACHEM-L  November 1999

PLASMACHEM-L November 1999

Subject:

Re: Cleaning Sample Containers

From:

"Bondarowicz, John" <[log in to unmask]>

Reply-To:

Analytical Chemistry using ICP's, DCP's, MIP's.

Date:

Tue, 23 Nov 1999 08:59:00 -0600

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (192 lines)

Geoff,

I think the answer to your question regarding equilibrium is "no equilibrium

will be reached".  The acidic solution will pull or leach the leachable
metals/contaminants indefinitely.  The majority of leaching (guess at 90%)
will
probably occur within a day or two.  Some analytes will never be entirely
leached (i.e., Ca from mold release in PE, PP ).  Your container is
relatively
neutral so the reaction (leaching) will be favored to go from neutral to
acid.
I assume your acid bath is fairly clean (low ppm contaminants).  It is
probably
a good idea to change your acids periodically to be safe.  Reagent grade
acids
are usually adequate for glassware cleaning.

Neutral solution leaching will eventually achieve some sort of equilibrium.

Some metals are adsorbed onto the container in neutral solutions which can
be
used to your advantage at times.  This was a step I was taught for
preconditioning homemade matrix modifiers for GFAA.  So, acidic
stabilization of
the analyte ions, and I believe occupation of adsorption sites by acid, is
an
important process.  Of course, omitting a preleaching step of your
containers
would yield some surprises.

For ultratrace work I favored the use/recycling of old Ultrex acid
containers
which if you think about it are preleached high quality Teflon.  I was a bit

surprised to learn that the manufacturers offered a modest deposit or even
charge for their disposal.  Were they for real ?  These used containers can
be
scarce.  Never return these valuable commodities to the supplier-they are
just
too useful.  As far as a choice of containers I think most common quality
(no
regrind) polymers will probably work fine but I have not reached many ICPMS
levels in my work.

Once the containers are selected the game changes to solution stability and
its
enemy is time.  Once you get containers which have been thoroughly cleaned
segregate them, have an idea of there history, (don't  collect sludge and
"clean" water in the same containers - it will never work), once you find a
good
container stay with it, ALWAYS collect blanks and consider using internal
standards of your target analytes.   You will find individual elements have
their own leaching/adsorbing personalities that you will come to know.

For some analytes you may be able to get away from expensive teflons.  This
will
require trial and error.  I think you (and your budget) may be pleasantly
surprised in your search.  Of course teflon is the "universal" choice but I
do
not know many labs that can afford hundreds of PTFE.etc. .containers.

There have been references to ultratrace sampling literature in this page
but I
am also interested in the groups common knowledge on this subject.

Teflon is nice but is it always worth the price differential ?

My recipe for trace metals container preparation:

1.      Overnight Surfactant soak (nonionic if possible but normal
labcleaners
are usually fine for getting rid of the dirt).

2.      Leach in 10% nitric for 3-24 hours min.   I used a Large Nalgene tub

with cover and reagent grade acid.

3.      Rinse with DI copiously.

4.      Air dry inverted containers in a nalgene pan.  Cover with dustless
lab
napkins.  Of course in a clean environment.

5.      When dry store in clean plastic bags.  "Zip-lock" are nice but don't

overstuff them.

6.      Segregate, segregate, segregate all your glass from other chemical
analysis procedures.  i.e., once a Se catalyzed reaction in done in glass
you
will never be able to remove all of it.  Similarly permanent Cr
contamination
with chromic acid washing which by the way is hard to beat for supreme trace

organic cleaning.

7.      Glass works well short term but some analytes like Ag, Si,...stick
to it
noticeably in short time (hours).  Nalgene PMP,  PP are economical, pretty
good
for day to day use, and last a long time.

8.       Air dry covered under dustless napkins

9.       If you are able perform these steps in different levels of clean
room
atmospheres - all the better but again what are your critical analytes and
are
they present in your dust.  I have seen great work done in manufacturing
labs
adjacent to dirty factories.  Same air in both.  Dirty floors.  Good
technique.

P.S.  The above is backbreaking work for those who have not had the daily
pleasure.  This is one job I do not miss.  One thing for sure when you
manually
clean your own glass is that it is done right so think about this if you are

having trouble.

I wonder if we were able to do F at trace levels with ICP, ICPMS would we
see
horrendous F leaching from PTFE type containers ?


Back to your question.  Will Cu "re-bind" on containers in your acidic bath.
I
do not think so.  They will favor the acidic solution environment.

One way to always be sure is to use controls, blanks, replicates.  It sounds
so
simple when you are using expensive and sophisticated techniques like ICPMS
but
this fundamental step is sometimes overlooked for the more "sexy" aspects of
the
analysis.

I was hoping to see more responses but perhaps this is thought as as very
basic
to the community.  Apologies if I was too basic.  Back to my day job.....

John Bondarowicz





______________________________ Reply Separator
_________________________________
Subject: Cleaning Sample Containers
Author:  "Geoff Veinott" <SMTP:[log in to unmask]> at chicago1
Date:    11/19/1999 8:27 AM


Dear Plasmachem: I posted this question on an analytical chemistry
discussion
group but did not get any replies. If it has been discussed before let me
know
and I will get the archived files.

When doing ultra trace analyses for metals by ICP-MS the recommended
cleaning
procedure for sampling containers is one of multiple washes in hot ultra
pure
acids and multiple rinses in ultra pure water. I am trying to understand the

process that is going on here. I assume that some of the contaminate metals
are
simply surface dirt but are other metals incorporated into the sample
container
material (tefelon or polypropylene for example). If so do these containers
have
a "binding capacity" for metals. So for example, if copper concentrations in
the
acid bath equal or exceed the concentration in the container material will
no
more copper be removed from the material with an equilibrium existing where
Cu
moves from the acid to the container as quickly as it is removed.
Geoff Veinott
Research Scientist
Department of Fisheries and Oceans
Environmental Sciences Division
Northwest Atlantic Fisheries Centre
PO Box 5667
St. John's NF.
CANADA
A1C 5X1
phone 709-772-7989
email [log in to unmask] <mailto:[log in to unmask]>

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