Precursor MZ

Calculate peptide precursor m/z for a given integer charge.

Description

Precursor m/z relates neutral peptide mass to a positive integer protonation charge.

Precursor m/z relates neutral peptide mass to a positive integer protonation charge. The proton contribution is added after dividing neutral mass by charge.^[1]

Calculate peptide precursor m/z for a given integer charge.

When to use Precursor MZ

Use this tool to calculate peptide precursor m/z for a given integer charge.

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 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, charge, protonMassDa using the field table and calculation rules, then run the tool.
Read precursorMz. 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
charge	Charge	number	Required
protonMassDa	Proton mass da	number	Required

Enter positive neutral/proton masses in daltons and a positive safe-integer charge. Return theoretical precursor m/z.

m/z=neutralMass/charge+protonMass

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
precursorMz	Precursor mz	number

json

{
  "input": {
    "neutralMassDa": 1000,
    "charge": 2,
    "protonMassDa": 1
  },
  "output": {
    "precursorMz": 501
  }
}

Limitations and assumptions

This assumes proton adduction only. Other adducts, negative charge and isotope peaks are not modeled.

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.

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 Isotope Charge Estimator: Infer peptide charge from measured isotope spacing and supplied isotope mass.

References

Precursor MZ — tool.io

Similar or alternative tools

Charge From Precursor MZ
Infer integer peptide precursor charge from neutral mass and observed m/z.
Isotope Charge Estimator
Infer peptide charge from measured isotope spacing and supplied isotope mass.