>Hello Paul
The D/H composition of tank gas depends on the industrial process used. The
"Exhaust Gas Process" for example uses membrane diffusion of gases from
petrochemical processing and gives extremely light delta values of around
-600 permil whereas electrolytically produced hydrogen is much heavier but
it's value  will depend on the water used. I have had values of -90 to -200
for different hydrogen cylinders reputedly from the latter source. The
steam reformation of methane gives values in between these two extremes but
the problem is that industrial suppliers of bulk hydrogen cannot guarantee
their sources and often provide tank gases of mixed origin. I use a
hydrogen generator connected to a small gas mixing plant constructed in the
lab. By adding some D20 to the water feed tank it is easy to produce large
volumes of hydrogen of several hundred permil and mix this with
isotopically lighter stuff. Another quick way of producing hydrogen of
controlled isotope composition is to inject water
( typically 1 microlitre at a time ) through a quartz tube packed with
chromium heated to 800 C.

Terry Donnelly
Isotope Geosciences Unit
Scottish Universities Research and Reactor Centre
East Kilbride
Glasgow G75 OQF
Scotland
phone   01355 270148 / 270154
fax     01355 229898
email [log in to unmask]