Retention Time Matching for LC-MS Peptide Identification
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Solution Overview
Problem
Current proteomic methods face challenges in accurately identifying and quantifying proteins due to insufficient mass accuracy in LC/MS analysis, leading to false identifications and complications from peptide modifications and overlapping sequences.
Innovation Solution
The method involves multiple chromatographic injections to exploit retention-time shifts of precursor and product ions, generating a catalog of protein profiles to accurately match and quantify proteins by normalizing input data sets and determining related ions within a predetermined retention time window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mass accuracy in LC/MS analysis is improved, then peptide identification accuracy is improved, but measurement precision remains insufficient due to instrument limitations
Solution Approach 1:
The patent transitions from relying solely on mass accuracy (one dimension) to incorporating retention time information as a second dimension for peptide identification. By normalizing retention times across multiple injections and combining them with mass data, the system overcomes the limitation of insufficient mass accuracy (10 ppm or larger) to achieve more reliable peptide identification.
Solution Approach 2:
The patent performs preliminary normalization of retention times across multiple chromatographic injections before peptide identification. This preliminary action creates a standardized retention time reference that can be reliably combined with mass data, improving the overall identification accuracy before the actual identification process occurs.
2Adaptability or versatility
If mass search window is widened to account for modifications, then more peptide variants are detected, but false identifications increase
Solution Approach 1:
The patent adds retention time normalization as a second dimension to constrain the search space. Even when the mass search window is widened to detect various modifications (improving adaptability), the normalized retention time criterion acts as a filter to eliminate false identifications (maintaining reliability), since modified peptides will still elute at characteristic retention times.
3Reliability
If multiple chromatographic injections are performed, then retention-time shifts are exploited for better identification, but analysis time increases
Solution Approach 1:
The patent performs preliminary normalization of retention times across multiple injections, creating a standardized reference that can be reused for identification. This preliminary processing allows the system to exploit retention-time shifts from multiple injections (improving reliability) while efficiently reusing the normalized data for subsequent identifications (mitigating time loss).
Solution Approach 2:
The patent creates a normalized retention time reference model from multiple injections that can be copied and applied to identify peptides in subsequent analyses. This copying approach allows the system to leverage the reliability gains from multiple injections without repeating the full normalization process for each identification task.
4Reliability
If retention time normalization is applied across multiple injections, then identification accuracy is improved, but data processing complexity increases
Solution Approach 1:
The patent applies parameter changes by normalizing retention times to a common reference scale across multiple injections. This transformation simplifies the comparison of peptides across different runs by converting variable retention times into standardized values, improving matching accuracy while managing processing complexity through systematic parameter transformation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of protein identification and quantification by distinguishing precursors and related product ions through retention-time shifts, reducing false identifications and improving peptide sequence determination.
Implementation Method 1
Separation of intact proteins or of their proteolyzed peptide products by liquid chromatography (LC)
Data Source
AI summary
A method for matching a precursor ion with one or more related product ions includes providing input data sets obtained from sample injections, each of the data sets including a precursor ion and one or more product ions, normalizing the input data sets in accordance with a single retention time for the precursor ion, determining which product ions are within a predetermined retention time window with respect to the single retention time, and, if a product ion is within the predetermined retention time window for a specified number of the input data sets, determining that the product ion is related to the precursor having the single retention time. An apparatus for analyzing a sample includes a chromatography module, a mass-spectrometry module in communication with the chromatography module, and control unit in communication with the chromatography module and the mass-spectrometry module.