Isotope Charge Estimator
Infer peptide charge from measured isotope spacing and supplied isotope mass.
Description
Isotope spacing varies inversely with positive charge.
Isotope spacing varies inversely with positive charge. A discrete search chooses the charge whose predicted spacing is closest to the measured spacing.1
Infer peptide charge from measured isotope spacing and supplied isotope mass.
When to use Isotope Charge Estimator
Use this tool to infer peptide charge from measured isotope spacing and supplied isotope mass.
Prepare the canonical sequence, peptide assignments, fitted assay parameters or upstream measurements requested. Keep corresponding entries aligned, use the stated mass and signal units, and remove FASTA headers before entering sequence text.
How to use Isotope Charge Estimator and understand its results
- Prepare the canonical sequence, peptide assignments, fitted assay parameters or upstream measurements requested. Keep corresponding entries aligned, use the stated mass and signal units, and remove FASTA headers before entering sequence text.
- Enter isotopeSpacingMz, isotopeMassDifferenceDa, maxCharge, spacingToleranceMz using the field table and calculation rules, then run the tool.
- Read estimatedCharge, predictedSpacingMz, withinTolerance. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| isotopeSpacingMz | Isotope spacing mz | number | Required |
| isotopeMassDifferenceDa | Isotope mass difference da | number | Required |
| maxCharge | Max charge | number | Required |
| spacingToleranceMz | Spacing tolerance mz | number | Required |
Enter positive spacing/mass difference, positive safe-integer maximum charge and nonnegative tolerance in m/z units. Search charges 1 through maximum, favoring the smaller charge on ties; return charge, predicted spacing and inclusive tolerance flag.
predictedSpacing_z=isotopeMassDifference/z; choose minimum absolute spacing error Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| estimatedCharge | Estimated charge | number |
| predictedSpacingMz | Predicted spacing mz | number |
| withinTolerance | Within tolerance | boolean |
{
"input": {
"isotopeSpacingMz": 0.5016775,
"isotopeMassDifferenceDa": 1.003355,
"maxCharge": 5,
"spacingToleranceMz": 0.01
},
"output": {
"estimatedCharge": 2,
"predictedSpacingMz": 0.5016775,
"withinTolerance": true
}
}Limitations and assumptions
No spectrum or isotope pattern is read. A very large maximum expands the search directly; supply a realistic bounded range. The closest charge can still fail tolerance.
Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors. A successfully returned false flag is an evaluated outcome; its meaning is explained above.
Alternative or Complementary methods
Use Charge From Precursor MZ: Infer integer peptide precursor charge from neutral mass and observed m/z. For a complementary task, use Precursor MZ: Calculate peptide precursor m/z for a given integer charge.
References
-
Isotope Charge Estimator — tool.io
Similar or alternative tools
- Charge From Precursor MZ
Infer integer peptide precursor charge from neutral mass and observed m/z.
- Precursor MZ
Calculate peptide precursor m/z for a given integer charge.