****************************************************************************** From: Karlheinz Hauff Date: Thu, 04 Mar 1999 20:42:00 GMT Subject: NH3 as reagent gas for pos. CI? Organization: Deja News - The Leader in Internet Discussion Dear group! So far, we did our nitrosamine analyses by capillary GC-MS on an old Finnigan ITD800 ion-trap, in positive CI-mode using Methanol as reagent gas, which worked quite nice. However, this kind of "low pressure"-CI is not possible on our new GCQ ion-trap with its external ion source. Trying CI pos with Methane, it turned out that Methane obviously is too "hard" for protonating volatile nitrosamines like Dimethylnitrosamine, resulting in a rather high level of fragmentation. Thinking about alternatives to Methane, I came onto ammonia, being regarded as "soft" CI gas. Therefore I would like to ask if anybody here on the board has experience in using ammonia for positive CI. Are there further requirements besides gas lines and pressure regulators made from stainless steel - should I use a special oil for the rough pump? Other hints to consider? Any suggestions for other CI-gases "softer" than Methane? I'd also be glad to get further tips regarding GC separation of nitrosamines. Thanks a lot in advance! Best regards, Karlheinz Hauff Bestfoods Europe Quality Assurance karlheinz.hauff@keinschrottknorr.ch (To reply to my personal e-mail, please remove 'keinschrott') -----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own ******************************************************************************* From: cody@jeol.com (Chip Cody) Subject: Re: NH3 as reagent gas for pos. CI? Date: Thu, 4 Mar 1999 20:59:41 GMT Organization: JEOL USA, Inc. Ammonia works very well for polar and/or basic compounds, and it is widely used. You should expect to see M+H+ for basic compounds and M+NH4+ for polar compounds. You'll see both species for many compounds. Ammonia is much less of a "hard" reagent gas than methane because of the difference in proton affinities. Isobutane is intermediate between methane and ammonia. It is a little bit more general than ammonia, but it produces less fragmentation than methane. If you can use ammonia for your analyses, it works very well. Just be careful to vent the pump exhaust and check the ammonia tank for leaks. Once you have used ammonia in a CI gas line, it tends to remain in the lines for a while. You can see some reagent gas spectra on our web site (www.jeol.com) in the tutorial on ionization methods under the Mass Spectrometry product section. A good general reference on CI is the book "Chemical Ionization Mass Spectrometry" by Alex G. Harrison, CRC Press 1983. -- "For purposes of ... New Jersey Right to Know Act. Contents partially unknown." |____________ |_ Robert B. Cody, Ph.D |________________________________ Product Development Manager |__ Mass Spectrometry |________________________ JEOL USA, Inc. |_ http://www.jeol.com |__________ e-mail: cody@nojunkmail.jeol.com |_ (REMOVE 'nojunkmail' TO REPLY) ============== Do not send me spam or advertising via e-mail !! ========= ****************************************************************************** From: david.bostwick@chemistry.gatech.edu (David Bostwick) Date: Fri, 05 Mar 99 14:42:08 GMT Subject: Re: NH3 as reagent gas for pos. CI? Organization: Georgia Institute of Technology, Atlanta GA, USA We generally use isobutane for CI, but we use ammonia when that doesn't work, or to confirm the MW. We also use ammonia for DCI, which causes less damage to the sample than vaporizing it from the solids probe. All of the internal plumbing for our 70SE is inert, so the only difference between gases in our system is that the transfer lines are stainless steel and the regulators are designed for ammonia, as you said above. We don't use ammonia a lot, and we change our roughing pump oil about every six months, so we haven't seen pump problems due to ammonia. David Bostwick School of Chemistry and Biochemistry Ga. Inst. of Technology Atlanta. GA 30332-0400 ****************************************************************************** From: "O.A. Mamer" Date: Fri, 05 Mar 1999 16:00:32 GMT Subject: Re: NH3 as reagent gas for pos. CI? Organization: Mass Spectrometry Unit, McGill University We have done a great deal of ammonia CI+. We use polypropylene tubing and stainless steel fittings, along with plastic regulators meant specifically for ammonia. For pump oil, we use just the regular high purity (water white) oil but change it more often (gets really chocolate brown - almost looks good enough to put on ice cream - if you hold your nose...). The nice thing about ammonia CI is that frequently ions are seen representing MH+, MNH4+, and apparently M+. The latter is really M + NH4+ - H2O. Good luck! Orval A. Mamer, PhD, Director, The Mass Spectrometry Unit, and Professor of Medicine, McGill University 1130 Pine Ave West Montreal Que Canada H3A 1A3 Tel 514 398-3661 Fax: 514 398-2488 E-mail: md82@musica.mcgill.ca ***************************************************************************** From: ricksfbrsc@aol.com (Ricksfbrsc) Subject: Re: NH3 as reagent gas for pos. CI? Date: 5 Mar 1999 01:54:25 GMT Organization: AOL http://www.aol.com It is also possible to use 10% NH3 in methane as a reagent gas and get the same spectra; however, the mixture is less corrosive and much easier on your pump oil. ******************************************************************************* From: Kenneth Chan Subject: Re: NH3 as reagent gas for pos. CI? Date: Fri, 05 Mar 1999 10:12:41 -0500 Organization: National Research Council of Canada Hello, I think you will prefer NH3 CI over methane for the simple fact that in classical CI NH3 leaves the ion source much cleaner than methane. Methane and isobutane tends to leave carbon deposits around the filament and must be clean frequently: we use to clean our CI source once every 8 hours!. I don't recall how often I have to clean the source when we did NH3 CI but it was much less. As for pump oil, we use the normal rotary pump oil but we also change it every 1-2 months. Be careful when handling ammonia, make sure that everything is stainless steel and that the valves do not use viton seals. I had a valve leak on me once. Instead use KelF or even Buna seals. Good Luck Kenneth H.N. Chan ****************************************************************************** From: John Barton Date: Mon, 08 Mar 1999 12:14:58 +0000 Subject: Re: NH3 as reagent gas for pos. CI? Organization: Imperial College, London, UK One important point is that you ensure that the seals (particularly the shaft seal) in your rotary pumps are made of nitrile NOT viton. Most rotary pumps shipped these days use viton seals for their greater chemical resistance, but ammonia is one of the few chemicals which degrades viton more than it does nitrile. If you use ammonia for any length of time with a rotary pump fitted with viton seals, you will get serious oil leakage. I don't know what make of pumps you use, but certainly Edwards pumps can still be fitted with nitrile seals. I recommend changing the oil every 6 months. Good Luck