Dear All,

I have been asked to investigate the use of cold fingers which have been
adapted to allow small quantities of nitrogen gas to be frozen into the
inlet volume of a dual inlet mass spec prior to isotopic analysis. My
limited experience with using molecular sieves to concentrate gases for
isotopic analysis have taught me to be somewhat wary of possible
fractionations associated with the process of absorbing and desorbing
gases from molecular sieves. I feel that any problems might be further
accentuated for small (micromole-level) quantities of gas.

I would be pleased to hear from anybody with any opinions or experiences
regarding the use cold fingers to freeze small amounts of nitrogen into
the mass spec inlet. Any suggestions regarding the quantities and
type of molecular sieve to be used would be gratefully received.

Cheers,

Steve Crowley

Stable Isotope Lab
Liverpool University
UK