Formula Used
The calculator builds isotope peaks by convolution. Each isotope contributes its exact mass
and natural abundance. For a formula, every atom adds another isotope choice.
Peak probability is found by multiplying the abundance values in one isotope combination.
Combinations with the same rounded mass are grouped together.
Relative intensity is calculated as:
relative intensity = peak probability ÷ base peak probability × 100.
The mass-to-charge value is calculated as:
m/z = (neutral isotope mass + adduct mass) ÷ charge.
If charge is neutral, the neutral isotope mass is shown.
How to Use This Calculator
Enter a chemical formula such as C8H10N4O2. Use normal element symbols and atom counts.
Select the charge state. Choose an adduct when your method forms protonated, sodium, potassium, or ammonium ions.
Use the threshold to hide weak peaks. Increase maximum peaks for complex formulas. Choose more decimals for high resolution comparison.
Press the calculate button. The result appears above the form and below the header. Export the same result as CSV or PDF.
Mass Spectrometry Isotope Pattern Guide
Mass spectrometry can show more than one molecular peak. Natural isotopes create a cluster around the main molecular ion. This calculator estimates that cluster from an entered formula.
Why isotope patterns matter
Every element has isotopes with different masses. Carbon has carbon twelve and carbon thirteen. Chlorine and bromine show stronger satellite peaks. Sulfur and silicon also change the shape. A predicted pattern helps confirm molecular identity before deeper interpretation.
Chemists compare measured peaks with calculated peaks. The match can support a proposed elemental formula. It can also reveal missing atoms, wrong charge states, or an incorrect adduct. The first peak is often called the monoisotopic peak. Later peaks are produced by heavier isotope combinations.
How this tool works
The tool parses the formula into elements and atom counts. It then combines the isotope masses and natural abundances. Each combination gives a probability and an exact neutral mass. The largest probability is normalized to one hundred percent. Very small peaks can be removed with the threshold setting.
The charge field converts neutral mass into m/z. Adduct mass can model protonated, sodium, potassium, or ammonium ions. A custom adduct option supports special laboratory methods. The peak limit keeps the table readable for larger formulas.
Best practice
Use a clean formula without spaces. Enter C6H6 for benzene or C8H10N4O2 for caffeine. Choose a threshold that matches the instrument noise. Low thresholds show more minor peaks. High thresholds make the result simpler.
Use enough decimal places for high resolution work. Compare peak spacing, not only peak height. A singly charged ion separates isotope peaks by about one m/z unit. A doubly charged ion separates them by about half a unit.
Exporting results is useful for notebooks and reports. CSV files fit spreadsheets. The PDF option creates a quick printable summary. Results should still be checked against calibration, resolution, and sample purity.
Limits and assumptions
Natural abundance values are average values. Real samples can differ slightly. Labeled compounds will differ much more. The calculation also groups close masses by selected decimals. That grouping is practical for tables, but it is not a full instrument simulation. Resolution, detector response, background subtraction, and centroiding can change displayed intensities in real spectra. Review isotope labels with care.
FAQs
What does this isotope pattern calculator do?
It predicts isotope peak masses, m/z values, probabilities, and relative intensities from a chemical formula. It helps compare expected molecular clusters with observed mass spectrometry data.
Which elements are supported?
The calculator supports H, C, N, O, S, Cl, Br, Si, P, F, and I. These cover many organic, biochemical, and halogenated formulas.
Can I use parentheses in formulas?
Yes. Formulas such as C6H4(Cl)2 and C2H5NO2 are accepted. Hydrate-style dot sections can also be entered when supported elements are used.
What does relative intensity mean?
Relative intensity compares each isotope peak with the strongest peak. The strongest peak is set to 100 percent, and all other peaks are scaled against it.
Why does charge change m/z spacing?
Mass-to-charge divides ion mass by charge. A doubly charged ion shows about half the isotope spacing of a singly charged ion.
What is an adduct mass?
An adduct mass represents ion attachment, such as hydrogen, sodium, potassium, or ammonium. It shifts the calculated m/z value while the neutral isotope pattern remains related.
Why are small peaks missing?
The threshold setting hides peaks below the selected relative intensity. Lower the threshold or raise the maximum peak limit to show more weak isotope peaks.
Are results suitable for final identification?
Use them as calculation support. Final identification should include calibration, instrument resolution, fragmentation data, retention behavior, and sample context.