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Tutorial 04 -- Elemental Formula


Elemental formula is a utility that will determine a list of possible elemental compositions for a given mass.


1  Select Elemental Formula from the Utilities option on the main menu, or click on the associated Speedbutton on the Toolbar.

2  Enter "100" (without the quotation marks) into the molecular weight box and click the 'Calculate' button.  Four possible hydrocarbons with a mol wt of 100 +/- 1 amu will appear in the results list.

3  Click on the check boxes next to O and N in the elements list to turn them on.  In each case, Min# will indicate 0 and Max# will remain blank.  This means that any and all possible combinations of this element (including none) will be included in the evaluation.

4  Click on 'Calculate' again.  In this case, 48 possible compositions will be found.  Many impossible compositions are filtered out by the utility, but the lists generated will often retain some highly improbable compositions.  If you click on any result in the list, additional information including an "unsaturation index" (rings + double bonds) and the electron configuration (OE or EE) will be displayed.  This can be repeated as desired for each composition in the list.  Click 'Close' on the Information panel to close it.

5  Click on the Molecular Ion box.  The 'Nitrogen Rule' box will also be selected automatically (it can be deselected if desired).  In this case, only OE+ ions that adhere to the "nitrogen rule" will be calculated.  Clicking 'Calculate' again will generate a much shorter list of 16 possibilities that meet these more restrictive conditions.

6  The bottom three elements default to Cl, Si and S.  These three elements are variable and can be changed.  Right-Click on Si.  A small popup window will appear with a list of alternative elements.  Double click on Br to replace Si with Br on the element profile.  Note that choosing an alternate element in this manner automatically selects it.  Click on the selection box to un-select Br.

7  You can restrict the range of compositions examined by selecting minimum and/or maximum possibilities for the elements, and by adjusting the tolerance for the analysis.  For example, to find only those species with a mass of 100 +/- 0.5 amu that could be molecular ions, contain 3-6 carbons, exactly 1 oxygen atom, and any possible number of nitrogen or chlorines, you would enter 100 and 0.5 in the mass and tolerance windows, enter 3 and 6 in the Carbon Min# and Max# windows, 1 and 1 in the Oxygen Min# and Max# windows, click on the N and Cl option boxes to turn them on, select the Molecular Ion and Nitrogen Rule options, and click 'Calculate'.  A total of 3 species will be found in this case.

8   Click Close to close the Elemental Formula calculator and return to the main MSC window.


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