Margaret (and others interested),

You will find a detailed description of a modified vesion of the DesMarais
trap in:

Taylor, B. E. and Beaudoin, G., 1993, MILES laser microprobe. Part I. system
description; in Current Research, Part D; Geological Survey of Canada, Paper
93-1D, p. 191-198.

Plus data regarding the separation of CF4, CO2, SF6, and SO2.  This trap  design
follows David DesMarais' original design, but is modified to permit more rapid
temperature cycling, pressure monitoring, and replacement of any part should
it eventually fail.  This modified trap design has served us very well.

Bruce Taylor
GSC, Ottawa