Question about HRMS:Phosphatidylcholines and phosphatidylethanolamines are common types of glycerophospholipids found in biological membranes. Because of the high amount of heteroatom content, electron impact mass spectrometry is a bad idea because the ions fragment too fast. For biological molecules, electrospray ionization is the most common method. A compound in the glycerophospholipid class was analyzed by low-res electrospray ionization. It produced peaks: 773 Th(100 percent abundance), and 795 Th(about 20% abundance). The question says these are not isotope peaks. The same compound was analyzed by high-rest EI mass-spec to have peaks at 772.5856 Th and 794.5680 Th. The question says to explain the 2 peaks’ presences in the high-resolution mass spectrometry.
For question #6, I came up with the molecular formula for C40H80NO8P for both classes of lipids but I was unsure of how to use that to come up with the actual molecular formula. The first lipid I found was dipalmitoylphosphatidylechloline with a molar weight of 734. But it's smaller than either of the 2 fragments. Then I added 6 methylene groups to come up with a molecular formula of C46H92NO8P. But I'm not sure how to get the molecular formula for both fragments(or if we actually need them). Can you help with this question or let me know of what I'm missing?