Dear Yuri,

We made our little diffusion pump long ago in-house. It worked very well,
although it did get dirty and needed frequent cleaning.  I didn't like the
cleaning part (life's too short!) so I changed to a KBr trap as a way of
removing fluorine. The KBr works fine, but I still have the feeling that
mercury is the best way of cleaning your gas.  The KBr trap is a lot safer,
and so we continue in this way.   The traces of NF3 that get through are
removed using a 13X mol. sieve.  In that way our d17O values are perfect.
Other possible salts are KCl and NaCl, which may be even better than KBr
because the Br is a rather sticky gas.

There is also a paper where stainless steel is used to trap excess flourine
(Akagi, T., Franchi, I.A. and Pillinger, C.T., 1995. Isotope analysis of
oxygen in minerals using Nd/YAG laser-fluorination: the use of
stainless-steel wool trap as a fluorine remover. Geochemical Journal, 29:
115-122.)

I would consider using the salts as a fluorine trap rather than the mercury.

Sincerely,

Zach