The M+2 peak in mass spectrum is found if the chlorine or bromine is present. The two molecular ion peaks (M+ and M+2) each contain one chlorine atom. The chlorine can either be 35Cl and 37Cl. 35Cl isotope has a formula mass of 78 and 37Cl has a formula mass of 80. A ratio of 3:1 describes the peak heights. This tells us that chlorine contains 3 times as much of the 35Cl isotope as the 37Cl one. Therefore, there will be 3 times more molecules that contain the lighter isotope than the heavier one.
Compounds that contain bromine have a different ratio. They have a 1:1 ratio. Bromine has two different isotopes as well, 79Br and 81Br. If there are two lines in a molecular region with a gap of 2 m/z units and are of almost equal heights, a bromine atom is present in the molecule.
After reading the information on this website I feel that I better understand the M+2 peak. I have put the link at the bottom of the blog if you would like to go check the website out for yourself!
http://www.chemguide.co.uk/analysis/masspec/mplus2.html
I agree with your difficulty understanding the concept of the m+2 peak. The web link that you listed did indeed help me. I had trouble understanding this concept at first as well. I suggest that if you are having trouble you may consult other text books or other web sits. Good luck!
ReplyDeleteThis seems to be the one of the muddiest points for the majority of us. However, it does seem you have a greater understanding of the material. I have also had difficulty understanding this concept as well. Some things that have been able to help me out have been reading through the chapters and looking at the example problems. Also, working on some of the problems at the back of the chapter. Good Luck.
ReplyDeleteSo there are alot of people having trouble with the M+2 peak concept including me. I am not very good at knowing which elements have isotopes and needless to say what kind of graphing they are going to have. Your website was helpful as well as your blog!
ReplyDeleteGood Luck!