Kyle Legate wrote:
Michael Press wrote:
Geraard Spergen wrote:
Michael Press wrote:
Geraard Spergen wrote:


C12 is 99% of all carbon, C13 is 1%, and C14 is about 1 part per 10^12.

Plants naturally have more C13 than animals so any substance (including
testosterone) produced from plants will have a higher C13 proportion
than the same substance produced by animals. Hard to believe there's
any difference in chemical reactions, it's probably due to photosynthesis.


What is photosynthesis if not a chemical reaction? At
least make your beliefs consistent. I suggest you take up
creationism. If that is not to your liking you will have
to eat your beliefs, because we have known for many
decades that chemical reaction rates for C12, C13, and C14
are different.


Oh man, that's harsh!

Differing chemical reaction rates cannot explain why plants have more
C13 to begin with. You have to explain why C13 is more likely to become
part of a plant than to become part of something else... or perhaps you
could propose that flora C12 is more likely to absorb an itinerant
neutron than fauna C12.

Chemistry is mostly about electrons, photons are absorbed in the
nucleus. I reasoned (perhaps incorrectly) that photosynthesis involves
photons being absorbed by neutrons and that C13 had a higher cross
section for photon absorption than did C12 and that this might account
for plants having a higher proportion of C13 than non-photosynthesizing
organisms. It may be a dumbass theory, but it can't hold a candle to
creationism.


But look, you are `reasoning' from your beliefs. Chemical
reaction rates are also about mobility of reactants. That
C13 is heavier than C12 affects its mobility.


Mobility has nothing to do with it. Heavier isotopes have a higher
activation energy, so they react slower. A phenomenon called hydrogen
tunneling can overcome this but it is extremely rare.

For what it's worth, I have done mass spec measurements on isotopically
labelled peptide mixtures (a much more complex sample than testosterone
isolated from urine) and can say the devices have become exquisitely
sensitive in the last 5 years, and they continue to double in
sensitivity roughly every year. One can only hope that the lab is using
recent state of the art to measure these samples.

This is so great! I love tuning in to a TV show, say about bass
fishing, and halfway through the program there's an in depth discussion
about amine blush in fiberglass boat layup!

R