LC/MS Unknown Identifications Using MSMS Libraries Part VIII: Identification of Unknowns with “Spectraless” Libraries

Th, 15.7.2021
| Original article from: Mass Spec Interpretation Services/James Little
This is a complimentary approach to the NIST search of MS/MS (Tandem) libraries. Seven other sessions in the series explore the use of NIST Search Software for the identification of unknowns.

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)
  • Acknowledgements

The past sections have focused on:

James Little/Mass Spec Interpretation Services
 

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