On Dec 5, 2008, at 3:04 PM, [EMAIL PROTECTED] wrote:
In reply to Edmund Storms's message of Fri, 5 Dec 2008 14:49:37
-0700:
Hi,
[snip]
I would like to clear up a little confusion. A mass spectrometer only
measures the mass/charge ratio of ions. These ions are made by
bombarding the gas with electrons.
Some MS use positive ions (e.g. Ar+).
Nevertheless, what I said still applies. This is simply a different
way to ionize a solid material to release the atoms as ions. The
method of separating the ions is the same regardless of how they are
made.
This causes the molecules in the
gas to ionize and to decompose. One of the decomposition products of
most organic molecules is CH+, which is found at mass 13. This
molecule is not present in the initial gas, but is only made during
the measurement. A mass is also found at 12 which is C+, which is
also only present after ionization. The gas Mizuno has is probably a
mixture of CH4 and various complex organic molecules. If C13 is
present, it will make ions at 13, 14, 15, and 17, which result from
the ions C13+.C13H+, C13H2+, and C13H4+. These molecules will also
be
seen at 12, 13, 14 and 16 in a normal spectrum based on C12. The
question people need to ask, if a lot of C13 was present, where are
the carbon-hydrogen ions based on this isotope?
Note that the starting product of the experiment was phenanthrene (see
http://en.wikipedia.org/wiki/Phenanthrene for a very enlightening
structure
diagram) which has at most 1 H atom attached to a carbon atom. IOW
when you
break phenanthrene up in a MS it is very likely that you will get CH
+ and
possibly some heavier CH combinations, such as C2H2 etc, which can't
be confused
with C13. However I wouldn't expect a lot of radicals with more than
1 H
attached to a C.
I expect Mizuno partially decomposed the phenanthrene to form the more
stable CH4, which would be mixed with the condensed solid after the
study. And yes, you are right, many complex ions will be produced
from the phenanthrene molecule. This spectrum should reveal
abnormalities if a lot of C13 is present. It simply is not proper to
base a conclusion on one mass in a mass spectrometer because many
things can combine to make the same mass/charge ratio.
Ed
Regards,
Robin van Spaandonk <[EMAIL PROTECTED]>
