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LC/MS Unknown Identifications Using MSMS Libraries Part V: NIST Structure Searches

Mo, 22.3.2021
| Original article from: Mass Spec Interpretation Services/James Little
A series of videos exploring the use of NIST Search Software for the identification of unknowns using tandem (MS/MS) spectra.

Mass Spec Interpretation Services/James Little: NIST Structure Searches

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 V will cover:

Detailed Handouts including tables of content are available in the LabRulezLCMS library.

  • Introduction of Presenter, James Little
  • Table of Contents
  • Series Topics -Help Files for NIST Search
  • NIST Software in General is “Windows Compliant”
  • Session Topics and Choice of Drawing Program
  • Critical Settings for Similar Structure Searches
  • Critical Settings for Exact Structure Searches
  • Critical Settings Turn Off Any Filtering Options Initially
  • Obtaining Structure from Drawing Program
  • Pasting Structure into NIST Search
  • Search for Similar Structures after Inserting Clipboard Structure
  • Search for Exact Structures
  • Tips for Displaying Similar and Exact Search Result with DeltaMass
  • Reverse Process: Sending Structures from NIST to Drawing Program
  • Using Compare Window to Display Multiple Spectra
  • Sending Structures Directly to Drawing Program
  • Live Demo YouTube Presentation
  • Presentation References (Internet Links)
  • Acknowledgements

Future parts will focus on:

  • 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

The past sections have focused on:

James Little/Mass Spec Interpretation Services
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