* X represents the relative intensity of the lowest mass ion
in an isotopic ion cluster. It is set at 100% for this calculation. The factor is multiplied by the number of atoms (n) of the designated element to calculate the intensity contribution from higher mass isotopes.
Michigan State University
The mass calculator on the right may be used to calculate the exact mass of a molecule based on its elemental composition. Simply enter an appropriate subscript number to the right of each symbol, leaving those elements not present blank, and press the "Calculate" button. Only the mass of the most abundant isotope, relative to C (12.0000), is used for these calculations. For compounds of chlorine and bromine, increments of 1.997 and 1.998 respectively must be added for each halogen to arrive at the higher mass isotope values.
The calculator on the left may be used to calculate the isotope contributions to ion abundances 1 and 2 amu greater than the molecular ion (M). Simply enter an appropriate subscript number to the right of each symbol, leaving those elements not present blank, and press the "Calculate" button. The numbers displayed in the M+1 and M+2 boxes are relative to M being set at 100%. Of course, compounds of chlorine and bromine have very large isotope abundances.
A more elegant and complete isotope pattern calculator has been created by Junhau Yan. To use this resource Click Here.
A useful resource, written by Jef Rozenski, calculates all possible combinations of H, C, N & O that give a specific nominal mass. To use this calculator Click Here.