LC/MS Unknown Identifications Using MSMS Libraries Part VIII: Identification of Unknowns with “Spectraless” Libraries
Mass Spec Interpretation Services/James Little: Identification of Unknowns with “Spectraless” Libraries
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 VIII will cover:
Detailed Handouts including tables of content are available in the LabRulezLCMS library.
- Introduction of Presenter, James Little
- Table of Contents
- Series Topics
- Introduction to Approach
- Origin of Term “Known Unknowns”
- Overall Process Including NIST Library Searches of EI and Tandem Spectra
- ChemSpider Internet Searches
- CAS Registry Using SciFinder and STN Express
- Summary Comparing ChemSpider and CAS Registry Approaches
- Example 1: SciFinder Search of CAS Registry for UV Additive in Polymer
- Example 2: SciFinder Search of CAS Registry for More Obscure Compound
- Example 3: ChemSpider Identification of Additive in Polymer by Monoisotopic Mass
- Live Demo YouTube Presentation
- Presentation References (Internet Links)