****************************************************************************** From: Ashok Deshpande Date: 02 Dec 1998 14:08:38 -0500 Subject: EC-NICI MS of PCBs Organization: * I am experimenting with parameters for the EC-NICI MS analyses of PCB congeners using a HP 5988 MS. In the SIM analyses, I have been able to detect the higher homologs of PCBs without any difficulty but some of the lower homologs are not detected at all. There seems to be no problem with the column or the MS since these homologs can be detected in the EI mode. Any ideas? Ashok Deshpande Research Chemist NOAA-NMFS Sandy Hook Marine Laboratory ****************************************************************************** From: "Rich Yelton" Date: Wed, 2 Dec 1998 22:36:25 -0500 Subject: Re: EC-NICI MS of PCBs Organization: EarthLink Network, Inc. I would try to run the experiment in full scan mode to make sure you are getting good CI on the lower homologues (reagent gas pressure optimized, reagent ion spectrum as expected). If you have good results then the problem may be in the SIM parameters i.e..mass/window. Best of Luck . Rich Yelton Spectratek Inc. http:members.aol.com/spectratek/spectratek.html ****************************************************************************** From: "Robert Gale" Date: Thu, 3 Dec 1998 15:26:15 GMT Subject: Re: EC-NICI MS of PCBs Organization: Environmental Contaminants Research Center We investigated NCI for PCBs toxaphene, etc. many years ago (mainly using methane). The general conclusion for PCBs was that EI/SIM was better. Refer to Crow, F. W., Bjoreth, Knapp, K. T., and Bennett, R. Determination of Polyhalogenated Hydrocarbons by Gas Chromatography - Negative Ion Chemical Ionization Mass Spectrometry (Anal. Chem. 1981, 53, 619-625) for information on responses in EI, NCI (methane), and NCI (oxygen-methane) [which seems to be more sensitive]. Sincerely, Robert Gale USGS BRD Columbia Environmental Research Center ****************************************************************************** From: "Colleen E. Rostad" Date: Mon, 7 Dec 1998 08:46:42 -0700 Subject: Re: EC-NICI MS of PCBs Organization: * Take a look at Biomed.Environ.Mass Spec., 1990, v. 19, p. 101-108, and Ron Hites & Elizabeth Stemmler's pubs in ES&T and Anal. Chem. She compared the response of HP's to Finnigan's GC/MSs. They had very different ionization responses for some PCBs, which I found to be true for PCBs on the Finnigan TSQ-46. I analyzed various mixtures of standards of mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, etc. PCBs (in the same GC) by NCI, with methane reagent gas. Despite excellent response for most of them, I had little to no response for many/most tri- and tetra- PCB isomers/homologs. Variation of the reagent gas pressure and source temperature made no difference, although Tom Leiker's law of "Keep it cold" for NCI was right on. I couldn't explain it by low halogens/carbon ratio, like the smaller PCBs. I just had to report my data as penta- through octa- PCBs, and hope for the best. My pubs have a disclaimer discussion that the lower homologs were not observed, which meant that I couldn't say much about degradation to the smaller PCBs, or dominance of the larger PCBs over the smaller ones, which would have been useful, considering that we had water, sediment and fish data from the same sites. Good luck! Colleen E. Rostad, PhD, Research Chemist US Geological Survey, MS 408 5293 Ward Road Arvada, CO 80002 Phone: 303-467-8251 E-mail: cerostad@usgs.gov