Mass Spec Explanation in HTML

Mass spectrometry can help determine the molecular formula and weight of a compound as well as provide isotope abundance data. Within a magnetic field the angle of deflection of charged particles is used to discover the relative masses of molecular fragments and ions. Several peaks are due to the contribution of isotopes. An isotope refers to an atom having the same atomic number but a different number of neutrons, subtracting or adding mass. The mass spectrum of methylene chloride has a base peak at m/z=49 consisting of the most abundant ion at 100% abundance. It also has a molecular ion peak at m/z=84 consisting of the molecular weight of methylene chloride at 80% abundance. By subtracting the base peak from the molecular ion peak, it can be determined that the resulting 35 corresponds to 35Cl. The difference of other molecular fragments can be looked at to verify chlorine’s presence such as 86(m/z)–51(m/z)=35 and 86(m/z)–49(m/z)=37, corresponding to the 37Cl isotope. The [M+2] rule also identifies the 37Cl isotope when looking at m/z=84, 86 and 86, 88. Each m/z peak can represent a variety of different molecular mass fragments. The base peak at m/z=49 has a molecular fragment of [ClCH2]+ and contributing isotopes [37ClC]+ and [Cl13CH]+. The peak at m/z=51 is composed of isotopes including [37ClCH2]+ and [37Cl13CH]+. The molecular ion peak at m/z=84 lacks a molecular fragment but shows due to the loss of one valence electron: [Cl2CH2]+. It also has isotope fragments of [Cl213CH]+ and [37Cl2C]+. The peak at m/z=86 is composed of isotopes including [37ClClCH2]+, [37ClCl13CH]+, and [37Cl2C]+. Finally, the last molecular peak at m/z=88 has these corresponding isotopes [37Cl2CH2]+ and [37Cl213CH]+. The peaks m/z=86 and 88 only have 60% and 20% abundance respectively, since both peaks are the results of isotopes. The 37Cl isotope has a 24% abundance naturally and 13C has a 1% abundance naturally. These low abundance percentages contribute to the smaller intensities