LC/MS Unknown Identifications Using MSMS Libraries Part III: More Detailed Discussion of MSMS Hybrid Search
Mass Spec Interpretation Services/James Little: More Detailed Discussion of MSMS Hybrid Search
MS/MS (Tandem) spectra can be used to identify unknowns employing library searches. This is accomplished in much the same approach as that employed for EI GC-MS with the NIST search software. The much improved NIST Search Version 2.4 is included with the 2020 library release.
I will attempt to introduce the user to the use of the NIST Version 2.4 search software employing NIST, Wiley, “crowd-sourced (MoNA)”, and user libraries for the identification of unknowns.
NIST has an ambitious program to extend their already comprehensive, high-quality MS/MS databases.
See the following link: NIST Pipeline for Extending MS/MS Libraries
This involves a very comprehensive process for selecting pertinent compounds for purchase and subsequent analyses. The problem with variability of the spectra is reduced by analyzing the samples on a variety of instruments at a variety of energy levels (20 steps). In addition, many different precursor ions and fragment ions are characterized (MSⁿ). This has already led to a very large high quality library of accurate mass MS/MS spectra in the 2020 release version (31K compounds/1.3 M spectra) and the effort is ongoing.
The Part III will cover:
Detailed Handouts including tables of content are available in the LabRulezLCMS library.
- Introduction to Presenter, James Little
- Table of Contents
- Series of Talks: LCMS Unknown Identifications Using MSMS Libraries
- Help Files for NIST Search
- NIST Software in General is “Windows Compliant”
- Presentation Topics
- Program Description and My Personal Experience
- Comparison to Standard versus Neutral Loss Spectrum
- Hybrid Search Results for Example
- Using DotProduct Instead of Score for Viewing Results
- DeltaMass Table
- Simple Examples Using Structures to Show DeltaMass
- Viewing Peak Matching Results by Sorting in Hybrid Search Results
- Merging Hybrid with Peak Matching Results
- Detailed Explanation of Hybrid Head to Tail Display
- Alternate Neutral Loss Comparison in Head to Tail Format
- Other Things to Consider with Hybrid Search for Unknown Identification
- Setting Up CriticalDefault Parameters for MS/MS Hybrid Search
- Live Searching Demonstration YouTube Video
Future parts will focus on:
- Part IV: Importing MSMS Spectra
- Part V: NIST Structure Searches
- Part VI: MS Interpreter Correlation of Substructure to MSMS Ions
- Part VII: Using and Creating Other MSMS Libraries
- Part VIII: Identification of Unknowns with “Spectraless” Libraries