This technical article comprises a discussion of the role of isotope peak intensities obtained using mass spectrometry in determining an elemental composition.
The atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes of that element. These different isotopes of an element have different masses that are almost an integer in value because of different numbers of neutrons in their nuclei; e.g., carbon has two primary naturally occurring isotopes, 12C and 13C. These two isotopes have respective integer masses of 12 and 13. Atoms of 12C have one less neutron in their nuclei than do atoms of 13C. This means that a mass spectrum of an ion containing carbon will be represented by peaks that are one m/z unit apart. The lowest m/z value peak represents an ion where all the carbon atoms are 12C. The peak one integer m/z value higher represents an ion where one of the carbon atoms is 13C. The peak one m/z unit higher than that represents the ion where two of the carbon atoms are 13C and so on.
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