Dear Dachun and hydrogen-isotopists,
In response to Dachun's observation that
the "D/H ratio of kerogen is greatly changed after the treatment
with HF" I want to offer my thoughts. If you don't use hydrofluoric acid,
you cannot remove silicates, including hydrogen-containing silicates.
Therefore, any "kerogen" that contains contaminating mineral hydrogen must
have a bulk hydrogen stable isotope ratio that reflects both organic and
inorganic hydrogen. Why would anybody want to measure the deltaD of
"total organic and silicate-hydrogen"? The term "kerogen" should be
reserved for substrates that have undergone extensive demineralization,
including the use of hydrofluoric acid.
Finally, it should be noted that some portion of organic hydrogen in
kerogen (hydroxyl, carboxyl, some amino-hydrogen) and strongly sorbed
water hydrogen in kerogen may be exchangeable with other ambient forms of
hydrogen, such as the hydrogen in hydrofluoric acid and water. Therefore,
any chemical treatment of kerogen with aqueous acids typically causes some
isotopic exchange of H in kerogen. It may be possible that some
commercial hydrofluoric acid has a weird deltaD value.