Charge From Precursor MZ
Infer integer peptide precursor charge from neutral mass and observed m/z.
Description
Precursor-charge inference searches positive integer charges for the theoretical m/z nearest an observation.
Precursor-charge inference searches positive integer charges for the theoretical m/z nearest an observation. The tolerance tests the resulting m/z error.1
Infer integer peptide precursor charge from neutral mass and observed m/z.
When to use Charge From Precursor MZ
Use this tool to infer integer peptide precursor charge from neutral mass and observed m/z.
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 Charge From Precursor MZ 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 neutralMassDa, precursorMz, protonMassDa, maximumCharge, chargeTolerance using the field table and calculation rules, then run the tool.
- Read estimatedCharge, predictedMz, 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 |
|---|---|---|---|
| neutralMassDa | Neutral mass da | number | Required |
| precursorMz | Precursor mz | number | Required |
| protonMassDa | Proton mass da | number | Required |
| maximumCharge | Maximum charge | number | Required |
| chargeTolerance | Charge tolerance | number | Required |
Enter positive neutral mass, observed m/z above supplied proton mass, positive safe-integer maximum charge and nonnegative m/z tolerance. Search 1 through maximum with smaller-charge tie preference, returning charge, prediction and inclusive tolerance flag.
predicted_z=neutralMass/z+protonMass; choose nearest predicted_z Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| estimatedCharge | Estimated charge | number |
| predictedMz | Predicted mz | number |
| withinTolerance | Within tolerance | boolean |
{
"input": {
"neutralMassDa": 1000,
"precursorMz": 501,
"protonMassDa": 1,
"maximumCharge": 5,
"chargeTolerance": 0.01
},
"output": {
"estimatedCharge": 2,
"predictedMz": 501,
"withinTolerance": true
}
}Limitations and assumptions
The proton-mass field is finite but not separately required positive. No spectrum, isotope selection or alternate adduct is assessed. Large maximum charges expand the loop directly.
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 Isotope Charge Estimator: Infer peptide charge from measured isotope spacing and supplied isotope mass. For a complementary task, use Precursor MZ: Calculate peptide precursor m/z for a given integer charge.
References
-
Charge From Precursor MZ — tool.io
Similar or alternative tools
- Isotope Charge Estimator
Infer peptide charge from measured isotope spacing and supplied isotope mass.
- Precursor MZ
Calculate peptide precursor m/z for a given integer charge.