Hello Jane, I remember that the late Tom Hoering at the Carnegie Institution had great success in using simple electrolysis (DC applied to graphite electrodes) in a large reservoir of slightly acidified water in a sealed Pyrex round flask with attached stopcock. Electrolysis of water produces D-depleted hydrogen gas, so Tom had added just the right amount of D-enriched water to obtain hydrogen gas "at the push of a switch" with a deltaD value around zero. I understand that he had to pass the wet hydrogen through a cold trap before using it at the mass-spec. This method seemed to be very reliable and low-cost. Best wishes, Arndt ******************** Arndt Schimmelmann Biogeochemical Laboratories Indiana University Department of Geological Sciences 1005 East Tenth Street Bloomington, IN 47405-1403 U.S.A. ph 812-855-0154 ph 812-855-7645 fax 812-855-7961 ********************