LC/MS Unknown Identifications Using MSMS Libraries Part VIII: 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:

• Part I: Overview of Software and User-Customized Configurations

• Part II: NIST Search Software and Libraries

• Part III: More Detailed Discussion of MSMS Hybrid Search

• 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