ncGTW

ncGTW performs reference-free profile alignment to detect and correct retention time (RT) misalignments in liquid chromatography–mass spectrometry (LC-MS) data, enabling compound-specific warping and improved feature alignment for proteomics and metabolomics analyses.

Key Features:

• Reference-free profile alignment: Aligns chromatographic profiles without relying on an external reference to accommodate sample-specific variability.
• Compound-specific warping functions: Estimates individual time-warping functions for different compounds to capture differing RT drifts within a sample.
• Neighbor-wise constraint edges: Incorporates constraint edges between warping functions of neighboring samples to leverage expected RT drift structures across run orders.
• Detection and realignment of misaligned features: Identifies misaligned feature groups and realigns them to improve downstream grouping and peak-filling.
• Addresses single-warping limitations: Designed to overcome limitations of methods that apply a single time-warping function per sample (e.g., standard XCMS approaches).
• Integration with XCMS output: Operates on standard XCMS feature groups to detect and correct misaligned feature sets.
• Validation on controlled data: Performance was evaluated using realistic synthetic data and internal quality control (QC) samples.
• Applicability to large-scale datasets: Targets large-scale metabolomics LC-MS experiments where misalignments can cause feature loss or incorrect grouping.

Scientific Applications:

• Proteomics LC-MS alignment: Improves RT alignment for peptide features to support accurate quantification and grouping.
• Metabolomics LC-MS alignment: Corrects compound-specific RT drifts to preserve metabolite features across many samples.
• Large-scale study QC and run-order correction: Detects systematic RT changes across run orders to maintain data quality in large cohorts.
• Feature grouping and peak-filling: Enhances grouping accuracy and peak-filling reliability by reducing RT misalignments.

Methodology:

Implements neighbor-wise compound-specific graphical time warping (ncGTW) via reference-free profile alignment, using compound-specific warping functions constrained by edges between neighboring samples to detect and realign misaligned feature groups; validation used realistic synthetic data and internal QC samples.