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HPLC for Pharmaceutical Scientists 2007 (Part 7B)

Nitrogen Rule: If the nominal molecular weight of an analyte appears to be an even mass number, the compound contains an even number of nitrogen atoms (or no nitrogen atoms). On the other hand, if the nominal molecular weight of an analyte appears to be an odd mass number, the com- pound contains an odd number of nitrogen atoms. | TABLE 7-5. Isotopic Abundances for Ions Containing Different Numbers of Sulfur Chlorine and Bromine Atoms Number of Cl Atoms Mass Number of Br Atoms 0 Number of Br Atoms 1 Number of Br Atoms 2 Number of Br Atoms 3 Number of Br Atoms 4 Number of Sulfur Atoms 1 Number of Sulfur Atoms 2 0 A 100 51.5 34.3 17.6 A 2 97.3 100 100 68.5 A 4 48.7 97.3 100 A 6 31.6 64.9 A 8 15.8 1 A 100 77.3 44.2 26.5 14.4 A 2 32 100 100 85.8 60.8 A 4 24.1 69.3 100 100 A 6 13.4 48.5 79.4 A 8 7.8 30 A 10 4.1 2 A 100 62 38.7 20.8 12.1 A 2 64 100 100 74 54.8 A 4 10.2 45 88.8 100 100 A 6 6.2 31.2 63.1 93.3 A 8 3.8 18.3 46.4 A 10 2 11.5 A 12 1.1 A 100 100 A 1 0.8 1.6 A 2 4.4 8.8 A 3 0.07 A 4 0.19 310 APPLICATIONS TO SMALL MOLECULES MS INTERPRETATION 311 molecular ions at m z 521 M H 523 and 525 of relative abundances 100 70 14. The isotopic intensity pattern is in good agreement with that of twit rhlAtinp oftitriQ CI Ivl p 7 rlnp tn flip iatk 35 1 T T 35 l37i l iwo chlorine atoms table _5 due to the ions C27H31O6 Cl2 C27H31O6 ci ci and C27H31O637Cl2. The characteristic isotopic patterns resulting from combinations of the isotope peaks can be used to ascertain elemental composition of the corresponding ion. 7.6.1.3 Nitrogen Rule. If the nominal molecular weight of an analyte appears to be an even mass number the compound contains an even number of nitrogen atoms or no nitrogen atoms . On the other hand if the nominal molecular weight of an analyte appears to be an odd mass number the compound contains an odd number of nitrogen atoms. This so-called Nitrogen Rule is very useful for determining the nitrogen content of an unknown compound. In the case of Verapamil Scheme 1 the molecular weight of the compound is 420Da indicating an even number of nitrogen atoms in the molecule. 7.6.1.4 Hydrogen Deuterium H D Exchange. The exchange of hydrogen for deuterium in organic molecules has been used in mass spectrometry for structural studies in both solution phase and gas phase. It also has wide applications