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Molecular Formula from Mass Spec Calculator

Identify candidate molecular formulas based on the molecular ion peak m/z ratio (MW) using nitrogen rule and carbon count estimations.

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Calculation Parameters

Specify your stoichiometry inputs.

Molecular Mass (m/z)

10 m/z500 m/z

Nitrogen Atoms

Calculated Result

Candidate Formula (Estimated)

C₂H₆O

Mass exact match: 46 u

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Expert Tip

The Nitrogen Rule states that organic molecules containing only C, H, O, N, and halogens have an odd molecular weight if they contain an odd number of nitrogen atoms.

How this Calculator Works

This calculator estimates a likely organic molecular formula from a molecular ion peak (m/z) mass spectrometry value. Adjust parameters below:

Molecular Mass (m/z): The primary mass peak representing the molecular weight (Default: 46)
Nitrogen Atoms: Select the suspected count of nitrogen atoms based on Nitrogen Rule (Default: 0)

The results are computed instantly and updated in the results panel on the right.

Formula & Methodology

Estimated Carbon Count = Math.round(m/z / 13.5) Hydrogen + Oxygen Mass = m/z - (Carbon * 12 + Nitrogen * 14)

Where:

m/z: Mass-to-charge ratio of the molecular ion.
Carbon: Atomic mass of 12.01 g/mol.
Nitrogen: Atomic mass of 14.01 g/mol.

Step-by-Step Calculation Example

To estimate the candidate formula for a mass spectrometer molecular peak at m/z = 46 with 0 nitrogens manually, follow these steps:

Identify the input parameters. For example:
- m/z = 46, Nitrogen = 0
Apply the formula:
1. Estimate carbon count: 46 / 13.5 ≈ 3.4 => choose 2 Carbons (Mass = 24). 2. If 1 Oxygen is present (Mass = 16), remaining mass is 46 - 24 - 16 = 6. 3. Hydrogen count = 6. Candidate molecular formula: C₂H₆O (Ethanol)
Verify the calculated value which is updated instantly in the results panel on the right.