Introduction

Evaluating a Statistical Method for Comparison of Mass Spectra of Novel Psychoactive Substance

Evaluating a Statistical Method for Comparison of Mass Spectra of Novel Psychoactive Substance

← Back to Webinar Series Page

Thursday, July 25, 2024 | 1:00 PM - 2:00 PM Eastern
Duration: 1 hour

Overview

Identification of novel psychoactive substances (NPS) based on comparisons of electron-ionization (EI) mass spectra continues to pose challenges in seized drug analysis. The continual evolution of NPS analogs, along with their related structural and positional isomers, results in EI spectra that visually appear very similar and are difficult to distinguish. 

A method to statistically compare EI mass spectra was developed to provide a more objective means of comparison. The method is based on the unequal variance form of the t-test, which is used to compare the mean intensities of corresponding mass-to-charge ratio (m/z) values in two spectra. At each m/z value, the null hypothesis (H0) states that the difference in mean intensity is equal to zero. If H0 is accepted for all m/z values, the two spectra are statistically indistinguishable, and in these cases, the two spectra represent the same substance. In contrast, if H0 is not accepted at one or more m/z value, the two spectra are statistically distinguishable. In these cases, the spectra represent two different substances.  

Current work focuses on evaluating the robustness and ruggedness of the statistical comparison method. For this evaluation sets of synthetic cathinone structural isomers, fluorobutyrylfentanyl (FBF) positional isomers, and fluoroisobutyrylfentanyl (FIBF) positional isomers were selected. Spectra for each compound were collected over time, at various concentrations, and on different instruments. The association of corresponding isomers and distinction of different isomers were demonstrated at the 99.9% confidence level. In instances of discrimination, the m/z values responsible for discrimination were determined, and in many cases, were defined as low-intensity ions that are not readily visible in the spectra. The statistical comparisons will be discussed in more detail, ions that are considered reliable for discrimination of each set of isomers will be identified, and recommendations to ensure accurate comparisons will be provided. 

Detailed Learning Objectives

  1. Attendees will be introduced to the statistical theory behind the comparison method. 
  2. Attendees will be provided with example applications of the method to distinguish structural and positional isomers of NPS analogs.
  3. Attendees will be provided with recommendations for accurate comparisons of mass spectral data. 

Presenter

  • Ruth Smith, Ph.D. | Professor, Department of Chemistry, Michigan State University


Funding for this Forensic Technology Center of Excellence webinar has been provided by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.

All Forensic Technology Center of Excellence live webinars are hosted using Zoom Webinar. Live webinars are archived and posted on our website within two weeks of their airing. Archived webinars do not require access to the Zoom platform.

The opinions, findings, and conclusions or recommendations expressed in this webinar are those of the presenter(s) and do not necessarily reflect those of the U.S. Department of Justice.

Contact us at ForensicCOE@rti.org with any questions and subscribe to our newsletter for notifications.


Related Content

Graphic Description – Medicolegal Death Investigation Frequently Used Data Elements for Toxicology and Seized Drugs

Date February 2024 Overview The National Institute of Justice (NIJ)-in partnership with its Forensic Technology Center of Excellence (FTCOE) at RTI International and the National Center for Health Statistics, Centers for Disease Control and Prevention (CDC)-convened a virtual Medicolegal Death…

White Paper – Forensic Community Drug Database Conceptualization

Date February 2024 Overview The National Institute of Justice (NIJ)-in partnership with its Forensic Technology Center of Excellence (FTCOE) at RTI International and the National Center for Health Statistics, Centers for Disease Control and Prevention (CDC)-convened a virtual Medicolegal Death…

Technical Note – The Use of Neutral Losses and Common Fragments Screening by QTOF in Forensic Laboratories

Date February 2024 Overview Quadrupole time-of-flight (QTOF) mass spectrometry is an advanced analytical technique that has some capabilities that make it particularly useful in screening in toxicology cases for unknown analytes. The technology combines the power of a quadrupole mass…