MS/MS Compound Identification Without Precursor Ion Information
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Solution Overview
Problem
Tandem mass spectrometry methods, such as SWATH, face challenges in identifying compounds without known precursor ion masses, and even known precursor ions 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 using a tandem mass spectrometer and processor to analyze product ion spectra without a priori 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 SWATH technique is used to scan mass range without known precursor ion mass, then the ability to analyze unknown compounds is improved, but the identification accuracy deteriorates due to confusion among multiple precursor ions within a mass window
Solution Approach 1:
The patent segments the complex task of compound identification into multiple steps: first selecting a subset of product ions from the full spectrum, then using these selected ions to search a dictionary of potential compounds. This segmentation allows the system to handle unknown precursors while maintaining accuracy by focusing computational effort on the most informative ions.
Solution Approach 2:
The patent extracts a subset of the most informative product ions from the complete product ion spectrum. By selecting only the most diagnostic ions for the identification process, the system removes distracting information from co-eluting precursors while retaining the essential features needed for accurate compound identification.
2Ease of operation
If a known precursor ion mass is used for identification, then the identification process is simplified, but the accuracy deteriorates when the compound is modified and the known mass does not represent the actual compound
Solution Approach 1:
Instead of starting with a known precursor mass and predicting its fragments (traditional approach), the patent inverts the logic by starting with observed product ions and searching for compounds that would produce them. This reverse approach eliminates the need to know the precursor mass in advance and automatically identifies both modified and unmodified forms.
Solution Approach 2:
The patent performs preliminary selection of a subset of product ions before the actual identification search. This preliminary action filters out noisy or non-diagnostic ions, making the subsequent dictionary search more efficient and accurate, while still allowing the system to handle modified compounds without prior mass information.
3Measurement precision
If all product ions are used for dictionary search, then the identification accuracy is improved, but the computational complexity and time increase significantly
Solution Approach 1:
The patent applies partial action by using only a subset of product ions for the dictionary search rather than all available ions. This subset is carefully selected to include the most informative ions, providing sufficient identification accuracy while dramatically reducing computational complexity and search time.
4Reliability
If multiple precursor-fragment combinations are measured for quantitation, then the quantitation capability is improved, but the device complexity and measurement time increase
Solution Approach 1:
The patent performs preliminary identification of compounds using a subset of product ions before quantitation. This preliminary action enables the system to quickly determine which compounds are present and their identities, allowing subsequent quantitation to focus only on relevant precursor-fragment combinations, thereby reducing overall measurement time while maintaining reliable quantitation capability.
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
Enables accurate identification of compounds and peptides from tandem mass spectrometry product ions without prior knowledge of precursor ions, effectively distinguishing between modified and unmodified forms, improving the precision of compound identification in complex samples.
Implementation Method 1
a precursor ion is selected, fragmented, and passed to a second analyzer
Data Source
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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.