Many elements in the periodic table have more than one isotope. The atomic mass of an element is cal — Analytical Chemistry Chemistry Question
Use of Isotopes in Mass Spectrometry
Many elements in the periodic table have more than one isotope. The atomic mass of an element is calculated based on the relative abundance of the isotopes. As an example, the atomic mass of chlorine is about 35.5 because the abundance of 35Cl is about three times the abundance of 37Cl. In mass spectrometry, instead of average atomic mass, the isotope peaks are observed. (35Cl 75.77%, 37Cl 24.23%, 12C 98.9%, 13C 1.1%, 79Br 50.7%, 81Br 49.3%)
Isotopes are quite useful in quantitative mass spectrometry.
In addition to the retention time (migration time), the ratio of M and M2+ ions was used as the qualitative criteria in the analysis of 2,3,7,8, tetra chlorinated dioxin (2,3,7,8–TCDD) by gas chromatography / mass spectrometry. Calculate the theoretical ratio of the two ions. The intensities of the isotopic species can be found by applying the following formula: (a+b)n , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and n is the number of chlorine atoms present.
Model Answer
0.77
Molecular ion is often selected in quantitative analysis. The intensity of the molecular ion needs to be corrected if the signal is interfered by other compounds. In the analysis of a non-halogenated compound with a molecular mass of 136, the molecular ion was selected for quantitative analysis. Propose a mathematical equation for calculation the corrected signal, if the analyte co-elutes (same migration time) with the compound n–butyl bromide.
Model Answer
Corrected signal = (m/z 136 signal) – 1.03 (m/z 138 signal)