****************************************************************************** From: Yining Zhao Date: Sun, 18 Oct 1998 17:51:24 +0200 (MET DST) Subject: MS for triglerides Organization: * Hi, Gentlemen: Recently I found an interesting phenomenon during LC-MS of lipids analysis. I am very much puzzled that I just observed M+. in triglycerides spectra instead of normal M+H signal. I tried both ES and APCI, the results are the same and I always got M+17 which is difficult to say from a cluster. For example, one triglyceride MS is m/z 833.4, I got 833.7 and 850.7 amu signals, could they be 834 (M+H) and 851 (M+NH4) ? is there some thing wrong with my MS accuracy ? Will you please tell if it's the MS accuracy problem or I should use 834 instead of 833.7 to look at the signal ? Thank you in advance Jonathan ZHAO ----------------------------------- ****************************************************************************** From: "O.A. Mamer" Date: Mon, 19 Oct 1998 10:12:56 -0400 Subject: Re: MS for triglerides Organization: Mass Spectrometry Unit, McGill University Triglycerides produce an M+NH4 (M+18) ion which fragments with the loss of water (18). The net effect is M + 18 - 18. Note that the apparent M+ now contains nitrogen and is an even-electron ion, NOT a molecular ion, and has the formula 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: "Rich Yelton" Date: 19 Oct 1998 21:24:36 GMT Subject: Re: MS for triglerides Organization: EarthLink Network, Inc. It is most likely that you are measuring the MH+ at m/z 834 and the M+17+ at m/z 851. You must take into consideration the number of Hydrogens on the molecule and the mass abundunace which results from this. The atomic weight of Hydrogen is 1.008. The mass observed for your molecule with the Ammonium ion (m/z 851) attached makes more sense for a Nitrogen containing compound. Best Regards, -- Rich Yelton Spectratek Mass Spectrometry Services Web: http://members.aol.com/spectratek/spectratek.html E-Mail: spectratek@aol.com