mzml-utils

Utilities for mzML mass spectrometry file processing, fragment ion calculation, and peak matching.

Installation

pip install mzml-utils

For development:

git clone https://github.com/lfu46/mzml-utils.git
cd mzml-utils
pip install -e ".[dev]"

Modules

Module	Description
reader	mzML file I/O with indexed and sequential access
ions	Ion searching, mass matching, tolerance calculations
xic	Extracted ion chromatograms (intensity vs retention time) over a run; isotope co-elution evidence for a precursor; peak boundaries and peak-quality metrics
chrom_extract	Peak table → chromatograms across many runs, every row column carried through (the Bioconductor chromExtract analogue)
isotopes	Exact-composition isotope distributions, for envelopes the averagine cannot express (halogen tags, heavy labels)
pairing	MS1 duty-cycle grouping, HCD-EThcD scan pairing
fragments	Fragment ion calculator (b/y/c/z/Y/oxonium), peak matching, false match rate
constants	Physical constants, amino acid masses, common ion lists
utils	Spectrum ID parsing, file finding, modification string parsing

Quick Start

Read an mzML file

from mzml_utils import MzMLReader

with MzMLReader("experiment.mzML") as reader:
    spec = reader.get_spectrum(12345)
    print(f"Scan {spec.scan_num}: {spec.n_peaks} peaks, {spec.activation_type}")
    print(f"Precursor: {spec.precursor_mz:.4f} m/z, charge {spec.precursor_charge}")

Search for diagnostic ions

from mzml_utils import search_ions, OXONIUM_IONS

results = search_ions(spec.mz, spec.intensity, OXONIUM_IONS,
                      tolerance=0.1, unit='Da', rel_threshold=5.0)

for name, match in results.items():
    if match and match['above_threshold']:
        print(f"  {name}: {match['mz']:.4f} ({match['rel_intensity']:.1f}%)")

Extract ion chromatograms (XIC)

from mzml_utils import extract_xic, extract_xics, OXONIUM_IONS

# One precursor / (glyco)peptide XIC from MS1 (source = a path or an open reader)
xic = extract_xic("experiment.mzML", 1204.564, ms_level=1,
                  tolerance=20.0, unit='ppm', rt_range=(62.6, 74.1))
print(f"NL {xic.max_intensity:.2e} at RT {xic.apex_rt:.2f} min")

# Several oxonium ions + TIC/base-peak in a single pass (ChromatogramSet)
cs = extract_xics("experiment.mzML",
                  {k: OXONIUM_IONS[k] for k in ("HexNAc", "NeuAc")},
                  ms_level=2, activation='HCD', tolerance=20.0, unit='ppm')
print(cs.rt.shape, cs.tic.shape, cs["HexNAc"].max_intensity)

ms_level=1 gives precursor XICs; ms_level=2 gives oxonium/fragment XICs (add activation='HCD' to skip ETD scans, precursor_mz=... for a single precursor). RT is the reader's native unit (minutes for Thermo msconvert mzML). The ms_level and rt_range filters are pushed into the reader (iter_spectra(ms_level=, rt_range=)), so a spectrum cache never decodes the scans an MS1 XIC would drop.

Check a precursor's isotopes at the trace level

from pyteomics import mass
from mzml_utils import isotope_distribution, isotope_trace_evidence

# Do M+1 / M+2 co-elute with M, and does anything co-elute one isotope BELOW it?
ev = isotope_trace_evidence("experiment.mzML", 991.5001, 4, rt_center=75.9)
print(ev.coelution, ev.pattern_cosine, ev.m_minus_1_coelutes)

# An envelope the averagine cannot express: a 4-bromo-Phe peptide (M+2 > M)
comp = mass.Composition(sequence="TPENFPSK") + mass.Composition({"Br": 1, "H": -1})
dist = isotope_distribution(comp, n_peaks=3, charge=2)
print(dist.mz, dist.abundance)          # pass distribution=dist to isotope_trace_evidence

Extract a peak table across many runs, with peak metrics

import pandas as pd
from mzml_utils import extract_chromatograms, chromatogram_rows

# One row per target: m/z, RT window, run name, plus any annotation columns
table = psms[["psg", "run", "mz", "rt_min", "rt_max", "ms2_rt"]].to_dict("records")
res = extract_chromatograms(table, mzml_paths, by="run", apex_rt="ms2_rt",
                            tolerance=10.0, nearest_valley=True)
df = pd.DataFrame(chromatogram_rows(res))   # row columns + apex, boundaries, area, FWHM, ...

Each row gets its own m/z and RT window, and one pass per run serves every row of that run. Without by=, every row is extracted from every run (cross-sample overlays). peak_metrics / peak_boundary port the Chromatograms, MsQuality and MetaboCoreUtils R code (boundaries, S/N, prominence, Kumler beta shape) and are pinned against those R functions. apex_rt= measures the peak whose boundaries contain the MS2 time, and nearest_valley=True stops R's left boundary from running to the start of a zero-filled trace. These are measurements, not verdicts: no threshold is applied.

Calculate fragment ions

from mzml_utils import FragmentCalculator, match_peaks, parse_modifications

mods = parse_modifications("N-term(229.1629),4S(528.2859),19K(229.1629)")

calc = FragmentCalculator("AGYSQGATQYTQAQQTR", mods, precursor_charge=3)
theoretical = calc.get_all_ions_flat()

matched = match_peaks(theoretical, spec.mz, spec.intensity, tolerance_ppm=20.0)
print(f"Matched {len(matched)} of {len(theoretical)} theoretical ions")

False match rate estimation

from mzml_utils import calculate_false_match_rate

fmr = calculate_false_match_rate(theoretical, spec.mz, spec.intensity,
                                  tolerance_ppm=20.0)
print(f"FMR (peaks): {fmr.fmr_peaks*100:.1f}%")
print(f"FMR (intensity): {fmr.fmr_intensity*100:.1f}%")

Pair HCD and EThcD scans

from mzml_utils import MzMLReader, group_ms1_cycles, pair_hcd_ethcd

with MzMLReader("experiment.mzML") as reader:
    scans = [
        {
            'scan_num': s.scan_num,
            'activation_type': s.activation_type,
            'precursor_mz': s.precursor_mz,
            'precursor_charge': s.precursor_charge,
        }
        for s in reader.iter_spectra()
    ]

cycles = group_ms1_cycles(scans)
paired = pair_hcd_ethcd(cycles, tolerance_ppm=10.0)
# paired: {hcd_scan_num: ethcd_scan_num}

Mass tolerance helpers

from mzml_utils import ppm_error, da_error, within_tolerance

print(ppm_error(204.087, 204.0864))      # ~2.9 ppm
print(within_tolerance(204.087, 204.0864, 20, 'ppm'))  # True

License

MIT