Analytical techniques for novel psychoactive substances (NPS) screening

Apr 21, 2023 | Blogs, Forensic, Toxicology | 0 comments

Read time: 10 minutes

The increased prevalence of novel psychoactive substances (NPS) in the recreational drug market has been a major contributor to the ongoing opioid crisis. NPS are newly emerging compounds designed to mimic existing recreational drugs and have become potent alternatives to controlled opioids. They are also frequently used as adulterants or cutting agents for commonly abused drugs. Continuous abuse of these substances can result in severe intoxication and, in some cases, fatal overdose.

Over the years, the surge in novel synthetic drugs has dramatically shifted the landscape of the drug market. What was previously characterized as a small subset of illicit drugs has become an expanding range of novel substances comprised of various chemistries, with each inducing unique physiological effects. The dynamics of this evolution continue to pose serious safety concerns for public health and law enforcement officials alike, resulting in a global public health crisis.

Learn more about NPS categories and trends >

The nature of this transformative shift has critical implications for effectively monitoring these emerging substances. Since their potency and composition are highly variable, it is critical to have fast, comprehensive drug screening approaches that are capable of accurately identifying emerging NPS in a timely fashion.

NPS detection: from screening to confirmation

Traditionally, the detection of illicit substances has been performed using immunoassays or gas chromatography coupled to mass spectrometry (GC-MS). However, these techniques have their limitations. Let’s take a closer look at these two approaches and why a third approach—liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)—has become the preferred method for NPS screening.

The specificity limitations of immunoassays for NPS screening

The use of immunoassays for designer drug screening is limited by their cross-reactivity, lack of specificity and high rates of false negative results. In addition, significant research and development is often required to develop antibodies specific to an increasingly wide array of new chemical structures. In fact, immunoassays often need multiple panels to detect the ever-expanding chemistries of designer drugs. This is a limiting factor that drastically slows the screening process. These limitations prove to be an analytical challenge given the dynamic and rapidly evolving nature of the NPS market.

Advantages Disadvantages
  • Easy sample preparation
  • Low cost per assay
  • Low sample volume
  • Fast results
  • Ready for automation
  • Not good for specificity
  • Cross-reactivity
  • Multiple assays required for each class of drugs
  • Does not always cover new NPS in the panels

The sample preparation constraints of GC-MS for NPS screening

GC-MS, by contrast, requires lengthy sample preparation to derivatize the analytes of interest. This technique is also known to suffer from long GC run times. These two limitations add significant time to the screening process. In addition, analyte identification often relies on library spectra, which may not be available for NPS that have recently emerged on the recreational drug market.

Read more about making the leap from GC-MS to LC-MS >

Advantages Disadvantages
  • More specific than immunoassay
  • Analyte-specific
  • Very sensitive
  • Requires derivatization
  • Identification based on library spectra (this may not be readily available for NPS)
  • Long GC times

The preferred method for NPS screening: LC-MS/MS

LC-MS/MS provides forensic toxicologists with the speed and confidence required to reliably identify NPS. Over the years, LC-MS/MS has become the preferred method for NPS analysis over traditional techniques due to its high levels of sensitivity and specificity, which can be leveraged for both screening and confirmation workflows. Mass spectrometry enables characterization of NPS by assessing their mass and fragmentation patterns and providing the necessary data to elucidate their ever-evolving molecular structures. The data acquired by mass spectrometers provide analyte-specific information, which enables accurate quantitation with far greater confidence than previously used techniques.

Advantages Disadvantages
  • Robustness, reliability and versatility
  • Accuracy and precision
  • Fast and sensitive
  • Requires less sample preparation and is compatible with generic sample preparation methods
  • Standards may not be available (but this can be overcome by using triple quadrupole, QTRAP and TOF systems)


When it comes to NPS screening using mass spectrometry, different types of instrumentation are available based on the type of analysis required. For targeted screening, triple quadrupole and QTRAP systems are the gold standard for fast, routine and highly sensitive detection and quantitation of NPS. Several scanning functions—such as multiple reaction monitoring (MRM) and enhanced product ion (EPI) scans—can be leveraged. MRM can be used to provide reproducible, selective and sensitive quantitation with excellent linear range, and EPI scans can be used to acquire full-scan MS/MS data that can be matched against mass spectral libraries for confident identification. As a result, the combination of triple quadrupole and QTRAP system functions allows for NPS quantitation and identification with MS/MS spectra in a single LC run.

Accurate mass spectrometry has emerged as a powerful and comprehensive solution for untargeted screening. Accurate mass systems are capable of characterizing NPS by reliably providing accurate mass, isotope pattern and MS/MS fragments that can be used to identify designer drugs using spectral library matching. The acquisition of accurate mass fragments enables forensic toxicologists to reliably capture a digital fingerprint of the drugs and metabolites present in a sample. This unique attribute enables retrospective data analysis without the need to re-inject the sample. This strategy is very attractive considering the ever-changing landscape of NPS in the drug market.

A clearer picture and a strengthened response

The adoption of mass spectrometry by forensic toxicology laboratories for the early identification and detection of NPS has provided public health professionals and law enforcement agencies with a clearer picture of the current NPS landscape and an early advisory of their emergence on the recreational drug market. This collective effort has proven to be an effective, team-based approach to staying ahead of transformative NPS trends and continuously monitoring their evolution. This critical information strengthens existing responses to the emergence of NPS and provides scientific intelligence to support NPS surveillance, monitoring, response efforts and drug policy formulation.

LC vs. LC-MS and what it means for your lab >

Do I need a single quadrupole or a triple quadrupole system? >