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. 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?
Ed
On Dec 5, 2008, at 2:22 PM, Jed Rothwell wrote:
Robin van Spaandonk wrote:
Don't forget that the analysis was outsourced. IOW the product of
the reaction
(presumably a black solid resembling soot) was sent offsite to be
analyzed,
implying a likely time between production and analysis of days at
least. Far too
long for a radical to continue to exist.
I have been meaning to raise that point. Maybe we should mention it
in the paper, although it seems kind of obvious.
Mizuno has various mass spectrometers in his lab, including some
fossils from the 1960s, but none as good as the Finnigan Mat Element
gadget. He bought a quadrupole mass spec himself to analyze effluent
gas on-line in real time. ("Quadrupole" -- which I find difficult to
pronounce -- means exactly what it sounds like: four polls, which
are at the heart of the gadget.)
- Jed
