MS Calc was developed in order to help students in a chemical instrumentation laboratory interpret their mass spectroscopy data. MS Calculator performs two types of analysis, chemical formula and isotope pattern.

Formula Calculator

A chemical formula calculator determines possible chemical formulae for the mass of a parent ion, fragment ion or difference ion. Up to six elements at a time (from a list of 12) are used in a chemical formula determination. The user enters upper limits for each element. For example, for the default settings (20 carbon, 40 hydrogen, and no nitrogen, oxygen, bromine or chlorine) a parent mass of 154 results in two possible chemical formulae: C11H22 and C12H10. Changing the limit on oxygen to three adds: C8H10O3, C9H14O2, C10H18O, C10H2O2, and C11H6O. It is left to the student to determine which chemical formulae make more chemical sense. Entering a fragment ion mass of 126 results in the following: C6H6O3, C7H10O2, C8H14O, C9H18, C9H2O, and C10H6. Tapping on the ‘Calc’ button under the Difference Ion label calculates the difference ion mass, 28, and the possible chemical formulae: CO and C2H4.

Isotope Calculator

Using the menu to select the ‘Isotope Calculator’ brings up a display with six chemical elements listed at bottom of the form. Enter the chemical formula of the ion, press the ‘Calc’ button and the isotope pattern will be displayed. Normally, the isotopes for hydrogen, nitrogen and oxygen are not included as their contributions are generally small and including them adds to the calculation time. However, if your are interested in the result, they may be included by checking the box for “Include H, N, & O…” in the ‘Select Elements’ form. Be aware, that the more isotopes that an element has the more it will influence the calculation time.

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