Chromatography Forum

I am doing a GC/MS NCI analysis using PTV injection and an Agilent 5975 MS with ammonia as a CI gas. I am perplexed why some CI filaments last forever, and other filaments start sagging within a few weeks and require replacement in less than a month. You can see the difference when checking the tune -- the good filaments show a constant abundance and a bad (saggy) filaments are characterized by a decreasing abundance when checking the tune. (The filament must line up with the tiny hole in the source body). I asked Agilent tech support about this, and they didn't have an answer. There is no air leak -- I am using SF6 to check for leaks and the instrument is very-very sensitive to SF6 -- a leak will show up almost immediately, even if the SF6 source is 3-4 feet away from the instrument.

It is a real pleasure to get one of these "good" filaments. Wonder if anyone would hazard a guess, as to what is going on here?

I have no idea as to the answer to your question; however, the guy that will be able to answer it is John Manura at Scientific Instruments Services, Inc. in Ringoes, NJ U.S.A. (http://www.sisweb.com). SIS manufactures filaments for all the makes of GC/MS instruments in the U.S.A. John knows more about GC/MS filaments than anyone I know.

Thanks ods-at-pacific--

I have had some CI filaments repaired by SIS -- haven't had time to really try them out yet, but they look like brand new filaments when SIS gets done with them. I like companies like that, that provide interesting, innovative products to test out. I believe, one time they offered a system that used pressurized corn starch to clean MS sources.