Way too brilliant! Nimal, I fell very ..., well, overshadowed by your way of thinking out the plots. I guess being overshadowed is not that unusual for me, but still, EXCELLENT!!

R. Steven Pappas, Ph.D.
Smoke Analysis Group
Centers for Disease Control & Prevention
4770 Buford Hwy, M.S. F-44
Atlanta, GA USA 30341-3717
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-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). [mailto:[log in to unmask]] On Behalf Of David K. Beck
Sent: Friday, September 30, 2011 12:53 AM
To: [log in to unmask]
Subject: Re: Mass 82

Nimal that is just brilliant!


David Beck
Metals Dept.
Lancaster Laboratories, Inc.
2425 New Holland Pike
Lancaster, PA  17601
717-656-2300, ext. 1232
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-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's).
[mailto:[log in to unmask]] On Behalf Of Nimal De Silva
Sent: Thursday, September 29, 2011 10:25 PM
To: [log in to unmask]
Subject: FW: Mass 82

Hi Glenn,

Even though your supplier doesn't seem to agree, by now several list
members convinced us that the culprit to your problem with M82 is most
likely to be Kr present in argon. However, you still may have a hard
time convincing your supplier that it is the case. I thought the
following calculation (and a plot) using the data you provided us may
give you good ammunition (which was also interesting and educational for

I calculated the difference as T2-T1(in Col-3 below) of the two
background measurements that you made at different masses using two
different tanks (in col-1 and col-2). Irrespective of the magnitude of
the background at a particular mass, this difference T2-T1 should
disappear for any background which remain almost constant and NOT
related to the "tanks", NOR due to Kr(For example, ArCl+, Ar2+, noise,
etc.). I have also tabulated the corresponding Natural Abundances of Kr
isotopes in col-4 (Note that, Kr80 was omitted as we do not have counts
at M80). Col-5 lists only those T2-T1 values(taken directly from col-3)
only for the masses where Kr isotopes are present(for convenience of

Mass  col-1  col-2   col-3         col-4         col-5

      Tank1  Tank2   T2 -T1        Kr            T2-T1 from

                     (net cts)     Abundance     col-4 for

                                                 Kr masses

77      3.4    3.9      0.5
78    613    628       15           0.35          15
79    129    132        3
81    222    223        1
82     69    593      524          11.6          524
83     70    597      527          11.5          527
84    356   3036     2680          57           2680
85      9.2   18        8.8
86    113    954      841          17.3          841
87     12     14        2

Now, in EXCEL if you plot Col-5 versus Col-4 (last two columns), in
spite of possible significant statistical fluctuation of small numbers,
you will still see a near perfect straight line with a correlation
coefficient of 0.9998 (attachments are not allowed); where five isotopes
of Kr together are proving that the "tank-to-tank" variation at M82 that
you observed IS in fact due to Kr. You may do the same for other tanks
as well to further strengthen your case.

Interestingly, major portion of the highest observed background counts
at M78 (613 and 628; very little from Kr) and at M81 (222 and 223, is
not from Kr) remain virtually the same in the two tanks, giving very
small difference T2-T1 for those masses.

Conversely, it looks like you may be able to use different tanks from
the particular supplier, to confirm the natural abundances of Kr
isotopes :)

Hope this is useful.



Dr. Nimal De Silva
Department of Earth Sciences
University of Ottawa
Ottawa, Ontario
Canada K1N 6N5
Phone: 613-562-5800 ext 6843
Fax: 613-562-5192
E-mail: [log in to unmask]