Multiclass analysis of psychoactive substances and NPS in oral fluid exploiting magnetic solid phase extraction (m-SPE) clean-up and HPLC-MS/MS

The recent rapid spread of new psychoactive substances (NPS) has become a topic of interest for researchers, healthcare professionals and law enforcement. NPS are defined as new narcotic drugs that are not controlled by the United Nations Conventions on Narcotic Drugs (1961) or Psychotropic Substances (1971), but which may pose a comparable threat to public health1. In recent years, the interest in so-called "alternative" matrices to conventional ones (plasma, whole blood, serum, urine) used for toxicological analysis in the clinical and forensic field is growing sharply. Among these, oral fluid (OF) offers a series of advantages that justify its use in different fields of application. OF is a relatively clean matrix, collection is simple, non-invasive, no special skills are required in sampling which can be supervised without violation of privacy, while reducing the possibility of specimen adulteration or substitution. The aim of the present work is to develop a new method for the determination of several substances of abuse and NPS in OF. Magnetic solid phase extraction (mSPE) was applied as a sample clean-up technique and subsequently an HPLC-MS/MS analysis was performed for the determination of the analytes of interest. The magnetic nanoparticles (MNPs), designed synthetized for this work, have a core-shell structure of Fe₃O₄ -SiO₂-C₁₈2. Their characteristics of MNPs, dimensional distribution and functionalisation degree, were subsequently verified using FT-IR, DLS and microscopic techniques. The proposed procedure was then validated following the international guidelines SWGTOX showing good results in terms of recoveries and matrix effect, which proved the efficiency of the clean-up step; also, the limits of quantification and identification are low, in the order of pg/mL for almost all the analytes considered, thanks to the enrichment factor in pretreatment and the sensitivity of the HPLC-MS/MS analysis. In conclusion, this magnetic extraction in the solid phase allows the sample to be pretreated in a simple way, with benefits both in terms of time and solvent consumption, avoiding centrifugation and filtration phases and giving a "green" footprint.