Chromatographic Retention Index for the Identification of Illicit Substances

Abstract

Introduction

New Psychoactive Substances have a high introduction rate into the market and represent a huge challenge from a regulatory and forensic point of view. Thus, the need for a method capable of identifying NPS, without the availability of certified analytical standards, arises.

Methods

The methodology of the work relies on the development of a GC/MS method; its validation; and the calculation of the Kovats’ Retention Index. This index was selected because it was reported as a tool for high-precision identification. A total of twenty-two substances were used: AM-2201, MAM-2201, JWH-081, JWH-210, N-ethylpentylone, 5-MAPB, 2-FA, 25C-NBOMe, o-CPP, p-CPP, U-47700, 5-MeO-MiPT, 5-IAI, Salvia divinorium, methiopropamine, THC, heroin, amphetamine, methamphetamine, MDMA, cocaine, and ephedrine.

Results

The method presented one Selectivity limitation (coelution of methiopropamine and methamphetamine). Resolution values were higher than 1.25, indicating signal separation. Separation Factor, Number of Theoretical Plates, and Tailing provided satisfactory results. Evaluation of Intermediate Precision indicated Relative Standard Deviations (RSD) that varied from 0.02 to 0.29%, lower than the literature. Robustness evaluation using a Fractional Factorial Design identified that changing the column polarity was the most influential factor, while column brand, gas flow, split rate, injector temperature, and ramp temperature did not interfere significantly. Retention Index was calculated without overlap and the Global Confidence Interval varied from 0,5 to 20,6 Retention Index Unity and the RSD varied from 0,02 to 0,29%, inferior to the range found in the literature.

Conclusions

The results of the development and validation indicate the adequacy of the method that uses Kovats’ Retention Index to identify NPS. The collection of Index calculated can be updated and made available to forensic institutes to be used as a tool in NPS identification.