John
Thank you for the chemistry lesson for today. I attached the two methods
referenced in the report. I did not find the detection limit mentioned
in the documents. Did I miss something??
Denis Ryskamp
Component Engineer
Paxar Americas, Inc.
170 Monarch Lane
Miamisburg, OH 45342
Ph: 937 865 2052
Fax: 937 865 2048
________________________________
From: John R. Sieber [mailto:[log in to unmask]]
Sent: Friday, September 29, 2006 1:47 PM
To: (Leadfree Electronics Assembly Forum); Denis Ryskamp
Subject: Re: [LF] Test for Cr6 on steel
Denis and all,
I have to ask if everyone understands the detection limit expressed for
this test. First, I admit I am not an expert in this area. Second, I
have not used the EPA test methods. My only contact with this issue is
the version of the method being developed by IEC TC111. I'm a member of
TC 111 Working Group 3. The test method uses a boiling water extraction
and compares the resulting solution after color development with a
standard solution just above the detection limit of the UV
spectrophotometer.
The only detection limit I believe can be given in any of these
extraction or digestion techniques is the estimate of the detection
limit for Cr6 in solution by the UV absorbance measurement. Is that the
detection limit you were quoted Denis? This is critical, because a
detection limit in solution has no direct link to the concentration of
Cr6 in the coating. Nobody really has good data for
extraction/digestion efficiency in all the different coatings. EPA test
methods are mostly based on extraction procedures and do not give the
true value in all cases.
To say it another way: Does the test method tell you there is < 2.0 ppm
Cr6 in the solution? If so, that may be correct, but you cannot
calculate the % Cr6 in the original coating unless you assume 100 %
digestion or extraction efficiency and no bias due to reduction of Cr6
to Cr3 or oxidation of Cr3 to Cr6 during the digestion.
Another question: Is the tested material within the scope of the EPA
test method or methods? Unless it says explicitly that the method is
intended for steel coated with yellow zinc chromate, the method probably
does not apply. There is a lot of confusion going on over these
various, similar looking test methods. I do not believe the ones
specifically developed for chromate coated aluminum or iron alloys use
the alkaline digestion. The standards to which I refer include ISO
3613, DIN 50993 and one or more from the automotive industry and its
suppliers. I have been told the ISO 3613 and perhaps others were
developed specifically for Cr6 coatings on steel or aluminum and not for
Cr3 (chromite) coatings.
I try to reduce the confusion in the world, but I fear this message
might increase it. Maybe I shouldn't throw out analytical chemistry on
a Friday afternoon.
Cheers,
John Sieber
PS Happy New Year to all you Federal employees out there!
At 12:48 PM 9/29/2006, you wrote:
Hello all
Just had a test of a steel shaft with yellow zinc chromate plating
tested for Cr6 with reference to EPA methode, alkaline digested using
3060A & analyzed using colorimetric 7196A (by UV-Vis Spectrophotometer).
Results came up ND. (Detection limit is 2.0 ppm)
Is there a yellow zinc chromate that is not Cr6?
Denis Ryskamp
Component Engineer
Paxar Americas, Inc.
170 Monarch Lane
Miamisburg, OH 45342
Ph: 937 865 2052
Fax: 937 865 2048
------------------------------------------------------------------------
-------
John R. Sieber, PhD
Research Chemist
National Institute of Standards and Technology
Chemical Science and Technology Laboratory
Analytical Chemistry Division
100 Bureau Drive, Stop 8391
Gaithersburg, MD 20899-8391 USA
[log in to unmask]
Tel: 1.301.975.3920
Fax: 1.301.869.0413
www.cstl.nist.gov/
Identification of commercial items in this document does
not imply endorsement by NIST or that items are
necessarily the best for the purpose stated.
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