Calculator Inputs
Example Data Table
| Sample | Formula | Ion Type | Approx. Exact Mass | Approx. M+1 | Approx. M+2 |
|---|---|---|---|---|---|
| Caffeine | C8H10N4O2 | [M]+• | 194.0804 | 10.30% | 0.67% |
| Chlorobenzene | C6H5Cl | [M]+• | 112.0080 | 6.53% | 31.98% |
| Acetone | C3H6O | [M+H]+ | 58.0419 | 3.32% | 0.25% |
Formula Used
Neutral exact mass: Exact Mass = Σ(element count × monoisotopic atomic mass)
Nominal mass: Nominal Mass = Σ(element count × integer mass number)
Ion mass: Ion Mass = Neutral Exact Mass + Adduct Shift
m/z: m/z = Ion Mass ÷ |charge|
M+1 estimate: Sum first-order heavy-isotope contributions, mainly 13C, 15N, 2H, 17O, 33S, and 29Si.
M+2 estimate: Add direct M+2 isotopes, such as 18O, 34S, 37Cl, and 81Br, plus paired M+1 combinations.
DBE: DBE = 1 + 0.5 × Σ[count × (valence − 2)]
How to Use This Calculator
- Enter a sample name for easier result tracking.
- Type the molecular formula exactly, including parentheses when needed.
- Select the ion type that matches your experimental ionization behavior.
- Choose the decimal precision for display and exports.
- Press the calculate button to show results below the header.
- Review exact mass, nominal mass, m/z, isotope estimates, and DBE.
- Use the graph to compare M, M+1, and M+2 intensities.
- Download CSV for tabular work or PDF for reporting.
Frequently Asked Questions
1. What does the molecular ion represent?
The molecular ion is the ionized form of the intact molecule before major fragmentation. In electron ionization, it is often the radical cation [M]+• and helps estimate the parent molecular mass.
2. Why are exact mass and nominal mass different?
Nominal mass uses whole-number mass numbers. Exact mass uses monoisotopic atomic masses with decimal precision. Exact values are essential when separating formulas that share the same nominal mass.
3. What causes a strong M+2 peak?
Elements such as chlorine, bromine, sulfur, selenium, and some metals create noticeable M+2 peaks. Chlorine and bromine are especially diagnostic because their isotope patterns are unusually strong.
4. Can this calculator handle adduct ions?
Yes. It supports common positive and negative forms, including protonated, deprotonated, sodium, potassium, ammonium, and selected multiply charged ions for practical spectrum interpretation.
5. What does DBE tell me?
DBE estimates rings and pi-bond equivalents in a formula. It is useful for checking whether a proposed composition fits expected unsaturation, aromaticity, or heteroatom content.
6. Are the isotope values exact spectrum intensities?
No. They are fast analytical estimates using major natural isotope abundances. They are very useful for screening, but full isotope envelope simulation is still better for publication-grade interpretation.
7. Can I enter formulas with parentheses or hydrates?
Yes. The parser accepts grouped formulas like (CH3)2CO and dot notation such as CuSO4·5H2O, provided all elements are included in the supported element list.
8. When should I export CSV or PDF?
Use CSV when you want spreadsheet analysis, batch comparisons, or lab records. Use PDF when you need a shareable report with visible metrics, composition tables, and the isotope chart.