Calculator
Example Data Table
| Formula | Adduct | Measured m/z | FWHM | Tolerance ppm |
|---|---|---|---|---|
| C8H10N4O2 | [M+H]+ | 195.0876 | 0.0030 | 5 |
| C17H19NO3 | [M+H]+ | 286.1438 | 0.0042 | 3 |
| C6H12O6 | [M-H]- | 179.0561 | 0.0025 | 5 |
Formula Used
The calculator first parses the molecular formula and totals each element. The neutral exact mass is the sum of every monoisotopic element mass multiplied by its atom count.
Theoretical m/z = (neutral exact mass + adduct mass) / absolute charge.
PPM error = ((corrected measured m/z - theoretical m/z) / theoretical m/z) × 1,000,000.
Resolving power = theoretical m/z / FWHM. Peak width in ppm equals FWHM divided by theoretical m/z, then multiplied by 1,000,000.
DBE = 1 + carbon - ((hydrogen + halogens) / 2) + (nitrogen / 2). This value is shown only when carbon is present.
How to Use This Calculator
Enter a molecular formula such as C8H10N4O2. Parentheses are supported, so grouped formulas can be tested. Select a common adduct or choose a custom adduct mass. Add measured m/z from the instrument report. Enter tolerance in ppm. Add FWHM or resolving power if available. Press calculate. Review mass error, isotope spacing, DBE, and export files.
High Resolution Mass Spectrometry Guide
Purpose
High resolution mass spectrometry helps chemists confirm molecular identity with exact mass evidence. It is useful in synthesis, natural product work, metabolomics, impurity testing, and forensic review. A small mass error can separate a likely formula from a false assignment. This calculator brings several checks into one simple workflow.
Exact Mass Review
The main value is the theoretical m/z. It is calculated from the neutral monoisotopic mass, selected adduct, and charge state. You can compare that value with the observed peak. The difference is shown in daltons and parts per million. PPM error is preferred because it scales fairly across low and high masses.
Resolution and Peak Width
Resolving power describes how well two close peaks can be separated. A narrow FWHM gives a higher resolving power. This matters when isotope peaks, adduct peaks, or interference peaks sit close together. The calculator also estimates M+1 and M+2 positions using charge corrected isotope spacing.
Formula Support
The parser accepts common organic and inorganic elements. It also supports grouped formulas with parentheses. The result includes neutral exact mass, average mass, nominal mass, mass defect, and elemental counts. These values help users spot typing errors and unreasonable formulas before reporting results.
Interpretation
A result within tolerance does not prove structure by itself. It supports a formula assignment. Isotope pattern, retention time, fragmentation, calibration quality, blank review, and sample history should also be checked. A result outside tolerance may signal wrong adduct selection, charge mismatch, calibration drift, or incorrect formula entry.
Reporting
Use the CSV option for spreadsheets and laboratory records. Use the PDF option for quick sharing. Keep the sample ID, instrument name, and notes complete. Good records make later review easier. They also make quality control discussions clearer. Always match the calculation method with your laboratory protocol.
FAQs
What does this HRMS calculator estimate?
It estimates exact mass, theoretical m/z, ppm error, resolving power, isotope spacing, DBE, and mass defect from a formula, adduct, charge, and measured peak.
Can I use negative ion mode?
Yes. Choose a negative adduct such as [M-H]-. You may also enter a custom adduct mass and charge for specialized workflows.
What is ppm error?
PPM error shows the relative difference between measured m/z and theoretical m/z. Smaller absolute ppm values usually indicate better agreement.
Does this confirm a chemical structure?
No. Exact mass supports a formula assignment. Structural confirmation needs more evidence, such as MS/MS, NMR, standards, or retention behavior.
What is FWHM?
FWHM means full width at half maximum. It describes peak width and helps calculate resolving power for the selected m/z value.
Why is the adduct important?
The adduct changes the ion mass. A wrong adduct can create a large ppm error even when the neutral formula is correct.
Can I export the result?
Yes. After calculation, use the CSV button for spreadsheet data or the PDF button for a simple printable report.
Does the calculator support grouped formulas?
Yes. It supports parentheses and square brackets in formulas. For example, C6H4(OH)2 can be parsed as a grouped formula.