How Can Relative Abundance Be Calculated?
In mass spectrometry, relative abundance typically refers to the natural abundance of isotopes-that is, the proportion of a given isotope present in a sample. This parameter can be measured using a mass spectrometer. The general procedure for calculating relative abundance is as follows:
1. Sample Collection
Collect samples that contain the isotopes of interest.
2. Ionization
Convert the molecules in the sample into ions using the ion source of the mass spectrometer.
3. Mass Spectrometric Analysis
Introduce the ions into the mass spectrometer, where they are separated based on their mass-to-charge ratio (m/z).
4. Measurement
Record the mass spectrum, which displays the relative signal intensities (peak areas or heights) corresponding to the different isotopes.
5. Calculation of Relative Abundance
Determine the relative abundance of each isotope by calculating the ratio of its peak area (or peak height) to the sum of the peak areas (or heights) of all isotopes.
For example, if a sample contains two oxygen isotopes, 16O and 18O, and the mass spectrum shows a peak area of 100 for 16O and 20 for 18O, then the relative abundance of 16O is 100/(100+20)=0.83, and that of 18O is 20/(100+20)=0.17.
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