Metabolite Signal Extraction From Lc Hrms

metabolite-signal-extraction-from-lc-hrms

Summary

Extraction of metabolite peaks from untargeted LC/HRMS data through a multi-stage algorithmic pipeline that begins with EIC candidate generation, followed by peak detection, property evaluation, and batch-wise retention time correction. This skill is essential for generating high-quality feature tables from population-scale metabolomics studies where sensitivity and specificity across hundreds of samples are critical.

When to use

Apply this skill when you have raw untargeted LC/HRMS data (mzXML, mzML, or netCDF format) from population-scale studies (n > 500 samples) and need to extract a comprehensive peaklist with aligned features across all samples. The skill is particularly valuable when you require 19+ chromatographic peak properties (peak area, S/N, tailing factor, isotope ratios, etc.) and must correct for retention time drift across multiple analytical batches.

When NOT to use

• Input is already a processed peak feature table or peaklist; use peak alignment/annotation instead.
• Targeted analysis with a small number of known m/z-RT pairs; use IPA_targeted function instead.
• Data from only a single analytical batch where retention time correction is not needed (though still applicable).

Inputs

• raw LC/HRMS data files in mzXML, mzML, or netCDF format
• IPA parameter spreadsheet (IPA_parameters.xlsx) with user-defined thresholds
• MS1-level high-resolution mass spectrometry scans
• retention time correction reference markers (for multi-batch studies)

Outputs

• individual peaklists per HRMS file in .Rdata and .csv formats
• peak alignment tables across all samples
• untargeted extracted ion chromatograms (EICs) in batch-aggregated form
• 19-property peak feature table (area, S/N, width, isotope ratios, tailing, gaussianity, etc.)
• batch-corrected retention time indices
• pairwise correlation lists for aligned peak heights and gap-filled tables

How to apply

Load raw LC/HRMS data (mzXML, mzML, or netCDF) into IDSL.IPA using the IPA_workflow function with a parameter spreadsheet. The algorithm first generates EIC candidates by binning mass spectral data across the full m/z range and applying intensity thresholding and noise filtering to retain only significant signals. Peak detection follows, calculating 19 chromatographic properties including peak area, signal-to-noise ratio (using baseline, xcms, and RMS methods), nIsoPair, RCS, peak width, asymmetry factor, and gaussian-like metrics. After individual-file peak detection, implement retention time correction across batches using endogenous reference markers for multi-batch studies, and finally perform peak alignment and annotation. Parameter selection is guided by a user-friendly spreadsheet (IPA_parameters.xlsx) that allows adjustment of thresholds, processing threads, and EIC output options.

Related tools

• IDSL.IPA (Primary extraction engine; implements EIC candidate generation, peak detection, property evaluation, mass correction, and batch retention time correction) — https://github.com/idslme/IDSL.IPA
• R (Execution environment for IDSL.IPA package)
• MZmine 2 (Comparative peak-picking tool; IDSL.IPA outperforms it in sensitivity, specificity, and speed)
• xcms (Comparative peak-picking tool; used as reference for S/N calculation method; outperformed by IDSL.IPA)
• MS-DIAL (Comparative peak-picking tool; outperformed by IDSL.IPA)
• RnetCDF (Optional dependency for processing netCDF/CDF mass spectrometry data) — https://CRAN.R-project.org/package=RNetCDF
• IDSL.UFA (Downstream integration: molecular formula annotation of aligned peaks) — https://github.com/idslme/IDSL.UFA
• IDSL.CSA (Downstream integration: clustering recurring ions to generate composite spectra) — https://github.com/idslme/IDSL.CSA

Examples

library(IDSL.IPA)
IPA_workflow("/path/to/IPA_parameters.xlsx")

Evaluation signals

• Individual peaklists contain all 19 chromatographic peak properties and match expected column schema (peak area, S/N, nIsoPair, RCS, asymmetry factor, tailing factor, etc.).
• Peak alignment tables show consistent number of detected features per sample with <5% missing values in gap-filled tables for valid peaks.
• Retention time correction reduces inter-batch RT drift to within ±0.1 minutes across batches (when reference markers are used).
• EIC output images (if PARAM0009='YES') display clean, resolved chromatographic peaks with appropriate signal-to-noise ratios and minimal baseline noise.
• Pairwise correlation lists identify expected isotope pairs (13C offset ~1.003 Da for doubly-charged ions, etc.) and known adduct relationships at biologically plausible correlation thresholds.

Limitations

• Requires high-resolution mass spectrometry data; applicability to low-resolution instruments (unit mass) is not stated.
• Multi-batch retention time correction relies on availability of endogenous reference markers; studies without reliable RTs standards may experience residual batch effects.
• Population-scale applicability emphasized for n > 500 samples; performance and computational cost for smaller studies not explicitly characterized.
• Positive and negative ionization modes must be processed separately; combined polarity analysis not supported.
• Peak annotation step requires integration with external tools (IDSL.UFA, IDSL.UFAx); standalone peak detection does not provide metabolite identity.

Evidence

• [readme] extracts peaks for organic small molecules from untargeted liquid chromatography high resolution mass spectrometry (LC/HRMS) data in population scale projects: "extracts peaks for organic small molecules from untargeted liquid chromatography high resolution mass spectrometry (LC/HRMS) data in population scale projects"
• [other] IDSL.IPA implements extracted ion chromatogram (EIC) candidate generation as the first algorithmic stage in a suite of algorithms that also includes peak detection, peak property evaluation, recursive mass correction, retention time correction across multiple batches, and peak annotation.: "IDSL.IPA implements extracted ion chromatogram (EIC) candidate generation as the first algorithmic stage in a suite of algorithms that also includes peak detection, peak property evaluation,"
• [other] Extract ion chromatograms by binning mass spectral data across the full m/z range to identify candidate signals. Apply intensity thresholding and noise filtering to retain only significant EIC candidates.: "Extract ion chromatograms by binning mass spectral data across the full m/z range to identify candidate signals. Apply intensity thresholding and noise filtering to retain only significant EIC"
• [readme] Calculating 19 chromatographic peak properties such as peak area, nIsoPair, RCS, cumulated intensity, R13C, peak width, RPW, number of separation trays, asymmetry factor, USP tailing factor, skewness using derivative method, symmetry using pseudo-moments, skewness using pseudo-moments, gaussianity, S/N using baseline, S/N using the xcms method, S/N using the RMS method, and sharpness.: "Calculating 19 chromatographic peak properties such as peak area, nIsoPair, RCS, cumulated intensity, R13C, peak width, RPW, number of separation trays, asymmetry factor, USP tailing"
• [readme] Retention time correction using endogenous reference markers for multi-batch large scale studies: "Retention time correction using endogenous reference markers for multi-batch large scale studies"
• [readme] IDSL.IPA is able to outperform similar peak picking tools such as MZmine 2, xcms, and MS-DIAL in terms of sensitivity, specificity and speed.: "IDSL.IPA is able to outperform similar peak picking tools such as MZmine 2, xcms, and MS-DIAL in terms of sensitivity, specificity and speed."
• [readme] Parameter selection through a user-friendly and well-described parameter spreadsheet: "Parameter selection through a user-friendly and well-described parameter spreadsheet"
• [readme] To process your mass spectrometry data (mzXML, mzML, netCDF), download the IPA parameter spreadsheet and select the parameters accordingly and then use this spreadsheet as the input for the IPA_workflow function: "To process your mass spectrometry data (mzXML, mzML, netCDF), download the IPA parameter spreadsheet and select the parameters accordingly and then use this spreadsheet as the input for the"