Athanor by arbastro
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The Formula finder plugin

Choose Plugins › Formula finder: Open Formula finder, enter the observed m/z, the ion and the ppm window, choose the elements, and it lists the formulas that match.

The Formula finder with the observed m/z, the ion, the ppm window and the elements to search.The Formula finder with the observed m/z, the ion, the ppm window and the elements to search.

Steps

  1. Choose Plugins › Formula finder: Open Formula finder.
  2. Type the Observed m/z, for example 195.0877.
  3. Choose the Ion (such as [M+H]+), the Window (ppm) (5 to start) and Electrons (Even-electron ion for most ESI ions).
  4. Under Elements, and the most of each, tick the elements to allow and set the most of each. C, N and O are ticked to start.
  5. The table lists each Formula with its Ion m/z, Error (ppm) and RDBE, smallest error first. Pick a row to put it on the page.
  6. Or press Check the selected structure to compare the formula of what you drew with the m/z.

The masses are monoisotopic (IUPAC and NIST). Formulas outside 0.2 ≤ H/C ≤ 3.1, N/C ≤ 1.3 and O/C ≤ 1.2 are left out, as is a negative or half-integer RDBE for an even-electron ion.

PluginsOfficial pluginsFour official plugins come installed and work signed out: Periodic table, Solution and buffer calculator, Formula finder and Solvent selector. Each opens a window from Plugins in the top bar.Names, properties and checksHow to calculate molecular weight, logP and other propertiesSelect the structure and choose Object › Chemistry › Calculate properties. The Compound info panel opens at Calculated, with the formula, exact mass, TPSA, donors, acceptors, rotatable bonds and the Lipinski rule-of-five checks.

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Last updated Nov 12, 2026