mzPAF Peak Annotation Format

About

mzPAF is a specification for a fragment ion peak annotation format for mass spectra, focused on peptides. This provides for a standardized format for describing the origin of fragment ions to be used in spectral libraries, other formats that aim to describe fragment ions, and software tools that annotate fragment ions.

• Official mzPAF homepage: psidev.info/mzPAF
• mzPAF documentation: mzpaf.readthedocs.io

Status

Updated: 2024-10-15

The specification has been resubmitted to the PSI Document Process and is undergoing final community review. It is anticipated to become a formal PSI standard near the end of 2024.

• The current DRAFT specification: mzPAF_specification_v1.0-draft15.pdf
• Example annotated spectra: Examples

In short

• mzPAF is a single string of characters, case sensitive, without length limit
• Multiple possible explanations are comma-separated
• Deltas of observed – theoretical m/z values are prefixed with a slash (/)
• Confidence of annotations are prefixed with an asterisk (*)

The basic format of each annotation is:

annotation1/delta,annotation2/delta,...

or:

annotation1/delta*confidence,annotation2/delta*confidence,...

For example:

b2-H2O/3.2ppm,b4-H2O^2/3.2ppm

or:

b2-H2O/3.2ppm*0.75,b4-H2O^2/3.2ppm*0.25

mzPAF supports:

• Annotations of multiple analytes: 1@y12/0.13,2@b9-NH3/0.23
• Mass deltas in ppm instead of m/z unit: y1/-1.4ppm
• Confidence levels per annotation: y1/-1.4ppm*0.75
• Advanced ion notation: [ion type](neutral loss)(isotope)(adduct type)(charge), e.g.: y4-H2O+2i[M+H+Na]^2:
  • Ion types:
    • Peptide ion series (a, b, c, x, y, z): y4
    • Unknown ions: ?
    • Immonium ions: IY
    • Internal fragment ions: m3:6
    • Intact precursor ions: p^2
    • A set of reference ions: r[TMT127N]
    • Named compounds: _{Urocanic Acid}
    • Chemical formulas: f{C16H22O}
    • Smiles: s{CN=C=O}[M+H]
    • Embedded ProForma annotations: 0@b2{LC[Carbamidomethyl]}
  • Neutral gains and losses: y2+CO-H2O
  • Isotopes: y2+2i
  • Adduct types: y2[M+H]
  • Charge states: ^2
• Multiple peaks per annotation: &y7/-0.001 and y7/0.000*0.95

Read the full DRAFT specificiation for more details and examples.

Getting started

mzPAF in Python

The mzPAF Python package can parse mzPAF strings into their components, convert to the JSON representation, or serialize back to an mzPAF string.

>>> import mzpaf
>>> annotations = mzpaf.parse_annotation("b2-H2O/3.2ppm*0.75,b4-H2O^2/3.2ppm*0.25")
>>> print(annotations[0].to_json())
{'neutral_losses': ['-H2O'], 'isotope': 0, 'adducts': [], 'charge': 1, 'analyte_reference': None, 'mass_error': {'value': 3.2, 'unit': 'ppm'}, 'confidence': 0.75, 'molecule_description': {'series_label': 'peptide', 'series': 'b', 'position': 2, 'sequence': None}}
>>> print(anno[0].serialize())
'b2-H2O/3.2ppm*0.75'

Learn more at the package documentation.

mzPAF regular expressions

The mzPAF specification includes regular expressions for parsing mzPAF strings. These can be used in any programming language that supports regular expressions.

Learn more at the mzPAF regex documentation.

mzPAF Lark grammar

mzPAF has also been defined as a Lark grammar.

Links

• The mzPAF GitHub repo: github.com/HUPO-PSI/mzPAF
• The GitHub repo for the related mzSpecLib standard: github.com/HUPO-PSI/mzSpecLib
• HUPO-PSI homepage: psidev.info