Example Data Table
| Example Formula |
Compound Type |
Expected Pattern Note |
| C6H12O6 |
Small organic molecule |
Carbon creates a visible M+1 peak. |
| C10H14N2 |
Nitrogen containing molecule |
Nitrogen shifts the exact isotope pattern. |
| C7H7Cl |
Chlorinated compound |
Strong M+2 peak appears from chlorine. |
| C6H5Br |
Brominated compound |
M and M+2 peaks are often similar. |
| CuSO4·5H2O |
Hydrated salt |
Metal and sulfur isotopes widen the envelope. |
Formula Used
The calculator builds a probability distribution for every element.
For each isotope, it uses exact isotope mass and natural abundance.
The molecular distribution is produced by repeated convolution:
P(m) = Σ P(a) × P(b)
Here, a + b = m. Each convolution adds isotope masses
and multiplies their probabilities. For charged ions, m/z is calculated as:
m/z = (neutral mass + adduct mass shift) / charge
Relative intensity is normalized against the strongest displayed peak.
The abundance column is normalized across the filtered output table.
How to Use This Calculator
- Enter a valid chemical formula, such as
C6H12O6.
- Use parentheses when needed, such as
Fe2(SO4)3.
- Select the charge state for m/z calculations.
- Choose the ion adduct that best matches your experiment.
- Set decimal places based on instrument resolution.
- Adjust the intensity threshold to hide weak peaks.
- Press the calculate button to show results above the form.
- Export the result table as CSV or PDF for reporting.
Calculating Isotopic Distributions for Mass Spectrometry
Understanding isotope envelopes
Mass spectrometry does not see a molecule as one lonely line. It sees a family of nearby peaks.
Each peak represents one isotopic version of the same formula. Carbon, hydrogen, nitrogen,
oxygen, sulfur, chlorine, bromine, silicon, and many other elements have natural isotope mixtures.
When atoms combine, their isotope probabilities also combine. The result is an isotope envelope.
Why distribution matters
A correct envelope helps confirm an elemental formula. It also helps compare simulated spectra with
experimental data. Chlorine gives a strong M+2 signal. Bromine often creates nearly equal M and M+2
peaks. Sulfur, silicon, and many carbon atoms broaden the envelope. These patterns are useful
fingerprints. They help chemists separate likely formulas from weak guesses.
How the calculator helps
This calculator parses a chemical formula and builds the isotope pattern by convolution. It multiplies
isotope probabilities across every atom. Then it groups peaks by selected mass precision. Low peaks
can be filtered, which keeps the table readable. You can adjust charge state and adduct type. This
makes the output useful for neutral masses and m/z values.
Practical interpretation
Start with the simplest expected formula. Use a small intensity threshold first. Then lower it when
minor peaks matter. Check the base peak, monoisotopic mass, and cumulative abundance. For high
resolution work, increase decimal places. For quick reporting, keep fewer peaks. Export the table
when you need documentation or further plotting.
Good habits
Natural isotope abundances are averages. Real samples can vary slightly. Instrument calibration,
resolving power, ion chemistry, and noise also affect measured spectra. Treat calculated peaks as
a guide, not as the final proof. Pair the envelope with accurate mass, retention behavior,
fragmentation, and sample knowledge. The strongest result comes from several matching clues.
Use the example formulas to test behavior before entering unknown compounds. Small molecules should
show compact clusters. Large organic formulas should show wider carbon driven spacing. Halogenated
formulas should show obvious two dalton structure. If a pattern looks impossible, recheck element
symbols, parentheses, charge, and chosen adduct. A clean input gives a cleaner spectrum. This habit
saves time during review. It also reduces errors when results are shared with colleagues later.
FAQs
What is an isotopic distribution?
It is the expected group of mass peaks created by natural isotopes in a molecular formula.
Why does carbon create M+1 peaks?
Carbon-13 is naturally present in small amounts. More carbon atoms increase the M+1 peak intensity.
Why do chlorine compounds show M+2 peaks?
Chlorine has two common isotopes. Their mass difference creates a strong peak about two daltons higher.
Can I use charged ions?
Yes. Enter the charge state and choose an adduct. The calculator converts neutral masses into m/z values.
Does this replace experimental spectra?
No. It provides a theoretical guide. Real spectra also depend on instrument settings, sample purity, and noise.
Which formulas are supported?
Common elements in organic, inorganic, and biochemical formulas are included. Unsupported elements trigger a clear warning.
Why are weak peaks missing?
The minimum intensity filter hides small peaks. Lower the threshold or increase the peak limit to show more peaks.
Can I export the results?
Yes. Use the CSV button for spreadsheets or the PDF button for reports and lab records.