Tandem Mass Spectrometer Compound Identification Without Precursor Ions
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Solution Overview
Problem
Tandem mass spectrometry methods, such as sequential windowed acquisition (SWATH), face challenges in identifying compounds without known precursor ion masses, and even known masses may not accurately represent the compound of interest due to modifications, leading to confusion among precursor ions within a mass window.
Innovation Solution
A system and method that utilize a tandem mass spectrometer and processor to analyze product ions without prior precursor ion information, selecting a subset of product ions, creating a list of candidate compounds by searching a dictionary of potential compounds, and identifying the compound based on predicted product ions, allowing for identification of peptides and their modified forms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If tandem mass spectrometry is performed without known precursor ion mass, then compound identification becomes possible in SWATH mode, but identification accuracy deteriorates due to confusion among precursor ions within a mass window
Solution Approach 1:
The method segments the product ion spectrum by selecting a subset of product ions that satisfy specific criteria (intensity threshold, mass-to-charge ratio range, etc.) to divide the complex identification problem into manageable parts, thereby improving identification accuracy without requiring precursor ion mass information
Solution Approach 2:
The method introduces an intermediary database search process that uses selected product ions to query a spectral library, acting as a mediator between the raw mass spectrometry data and compound identification, enabling accurate identification without direct precursor ion mass information
2Ease of operation
If precursor ion mass is used for compound identification, then identification process is simplified, but identification becomes inaccurate when the compound is modified
Solution Approach 1:
Instead of using precursor ion mass to predict product ions, the method inverts the approach by using observed product ions to identify the precursor compound through database searching, which remains valid even when the precursor is modified and its mass is unknown or inaccurate
3Quantity of substance
If all product ions are used for database searching, then comprehensive coverage is achieved, but computational complexity and time increase
Solution Approach 1:
The method extracts only the most informative subset of product ions from the complete spectrum by applying selection criteria (intensity thresholds, mass-to-charge ratios, etc.), removing redundant information and significantly reducing database search time while maintaining identification accuracy
Data Source
AI summary
Systems and methods are provided for identifying a precursor ion without using any a priori precursor ion information. In one method, a sample is analyzed using a tandem mass spectrometer, producing at least one measured product ion spectrum from a precursor mass-to-charge ratio range. The at least one measured product ion spectrum are received. A subset of measured product ions is selected from the at least one measured product ion spectrum. A list of candidate compounds is created by searching a dictionary of potential compounds that includes one or more predicted product ions for each of the potential compounds using the subset of measured product ions. A candidate compound on the list is selected as the identified compound. In another method, the measured product ions are assumed to correspond to shortened forms of the peptide and a protein database is searched for shortened forms of the peptide.