Details will be in the 2007 edition of the United States Pharmacopeia. Try
www.usp.org for pricing information. Be warned it's expensive, updated every 3-4 months, and copyrighted ( so people can't send scanned copies in email ).
If you can, find a local pharmaceutical company or institution library/laboratory that is prepared to let you read their copy.
If you are testing gases for conformity to the USP, you will be required to demonstrate that you have convenient access to the latest edition, so your employer should purchase it....
Bruce Hamilton