Spectrum Preprocessing And Normalization

spectrum-preprocessing-and-normalization

Summary

Preprocess MS/MS spectra from raw instrument data into normalized, standardized feature representations suitable for machine learning and cross-modal retrieval tasks. This skill prepares spectra for contrastive embedding by cleaning noise, normalizing intensity values, and aligning metadata.

When to use

Apply this skill when you have raw MS/MS spectra in MGF or other standard formats that need to be ingested into a machine learning pipeline for cross-modal matching against molecular structures, or when spectra from different collision energy levels or instruments require standardization before comparative analysis.

When NOT to use

• Spectra are already embedded in feature space (use this skill before embedding, not after)
• Input is a pre-aggregated spectral library or consensus spectrum (preprocessing assumes raw instrument-level data)
• Metadata (precursor m/z, collision energy) is missing or cannot be reliably reconstructed

Inputs

• MS/MS spectrum file (MGF format)
• Raw Spectrum object with peaks and metadata (from matchms)
• Collision energy level (low, medium, or high)

Outputs

• Normalized Spectrum object with cleaned peaks and validated metadata
• Precursor m/z value (scalar)
• Spectrum feature vector ready for neural encoding

How to apply

Load MS/MS spectrum data using matchms (e.g., from MGF files via load_from_mgf()). Apply spectrum_processing() to normalize intensities, remove artifacts, and validate metadata fields such as precursor_mz and collision energy. Extract the precursor m/z (often adjusted by subtracting 1.008 for protonated [M+H]+ ions) to enable subsequent mass-based filtering and library search. The processed spectrum object should retain both the normalized peak intensities and validated metadata for downstream embedding and similarity scoring.

Related tools

• matchms (Load and standardize MS/MS spectra from MGF files; provide Spectrum objects with peak and metadata accessors) — https://matchms.readthedocs.io/en/latest/
• PyTorch (Encode preprocessed spectra into normalized tensor representations for contrastive learning) — https://pytorch.org/
• rdkit (Validate and extract molecular properties (e.g., mass) for cross-modal alignment with spectrum precursor m/z) — https://rdkit.org/

Examples

spectrum = spectrum_processing(spectrum); query_ms = float(spectrum.metadata['precursor_mz'])-1.008; ms_list=list(load_from_mgf('spectra.mgf'))

Evaluation signals

• Spectrum object retains all required metadata fields (precursor_mz, collision_energy, SMILES or InChI if available)
• Peak intensities are normalized to a consistent scale (e.g., 0–1 or 0–100) with no NaN or infinite values
• Precursor m/z computed as float(spectrum.metadata['precursor_mz'])-1.008 matches expected m/z range for the compound class
• Output spectrum can be successfully passed to model_inference.ms2_encode() without shape or type errors
• Preprocessing reduces noise (removes low-intensity peaks below instrument noise floor) while preserving diagnostic fragment peaks

Limitations

• Preprocessing quality depends on MGF metadata completeness; missing or malformed precursor_mz or collision energy may compromise downstream retrieval accuracy
• The m/z adjustment (-1.008 for [M+H]+) assumes protonation; non-standard ionization modes (e.g., [M-H]−, [M+Na]+) require alternative adjustments
• Normalization strategy is not explicitly detailed in the README; the choice of intensity scaling (linear, log, square-root) may impact contrastive embedding quality
• No explicit handling of variable-length spectra or missing peak lists documented; edge cases with sparse or empty spectra may cause failures

Evidence

• [other] Load MS/MS spectrum data and molecular structure datasets (SMILES or SDF format) using matchms and rdkit.: "Load MS/MS spectrum data and molecular structure datasets (SMILES or SDF format) using matchms and rdkit."
• [other] Preprocess spectra and convert molecular structures to graph representations using rdkit and PyTorch Geometric.: "Preprocess spectra and convert molecular structures to graph representations using rdkit and PyTorch Geometric."
• [readme] spectrum = spectrum_processing(spectrum): "spectrum = spectrum_processing(spectrum)"
• [readme] query_ms = float(spectrum.metadata['precursor_mz'])-1.008: "query_ms = float(spectrum.metadata['precursor_mz'])-1.008"
• [readme] ms_list=list(load_from_mgf(".../.mgf")): "ms_list=list(load_from_mgf(".../.mgf"))"