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