****************************************************************************** From: "GC" Date: Tue, 25 Jul 2000 17:03:09 GMT Subject: Negative CI and CH4 Organization: Guest of ProXad - France Hello I'm new in using CI with a mass spectrometer with an ion-trap GCMS. We have a system with CH4 ionization gas. Is methane a good CI gas for the detection of pesticide residue in negative mode ? Is NH3 better? and for positive mode ? Someone tested the difference or can give me a bibliographic reference? Thanks ----- my real address is costaglixxx@xxxavignon.inra.fr (remove the 6 x to mail) ****************************************************************************** From: "David Sparkman" Date: Tue, 25 Jul 2000 10:37:48 -0700 Subject: Re: Negative CI and CH4 Organization: CompuServe Interactive Services I was not aware that you could do electron capture negative ionization with a quadrupole ion trap. CH4 is a good source of low-energy electrons required for electron capture negative ion formation in beam type instruments such as a transmission quadrupoles. Regards; O. David Sparkman Consultant-At-Large ods@compuserve.com ****************************************************************************** From: "David Sparkman" Date: Wed, 26 Jul 2000 07:30:58 -0700 Subject: Re: Negative CI and CH4 Organization: CompuServe Interactive Services OK! I was wrong. Because I spent so much time as the Varian Saturn product manager, I think internal ionization when I think about ITs. You cannot easily do ECI on an internal ionization IT. The Finnigan GCQ (now the PolarisQ) is an external ionization IT and, as sush, does do electron capture ionization. And, yes, CH4 is a good gas to produce low energy electrons required for this type of ionization. Regards; O. David Sparkman Consultant-At-Large ods@compuserve.com