Evaluating the Suppression Tolerance of a Novel Walk-up Desktop Trace Detector

Evaluating the Suppression Tolerance of a Novel Walk-up Desktop Trace Detector

Natalie Dunna, Lance Hileya, Charles Liddella, Peter Lukea, David Douceb, Ashley Sageb,Scott J. Campbellc and John Moncurc
aMass Spec Analytical Ltd, Future Space, UWE North Gate, Filton Road, Bristol, BS34 8RB, UK. bWaters Corporation, Stamford Avenue, Altrincham Road, Wilmslow, Cheshire SK9 4AX UK. cSpectralWorks Ltd, The Heath Business and Technology Park, Runcorn, Cheshire, WA7 4EB, UK.

Published 13th TEDD Workshop, Dublin, Ireland. June 2024.

Overview

Purpose:

Purpose:Determine the tolerance of a new thermal desktop threat detection system to common interferents that can suppress performance, create false positives/negatives, produce large background noise, or simply inhibit detection.

Method:

  • Samples analysed by TD-MS
  • Robust mass analysis using variable cone voltage
  • Negative APCI mode analysis

Quantification:

  • 650 swabs processed in total
  • 500+ Environmental swabs acquired from real-world locations
  • 3 Targets (PETN, RDX, TNT) selected across three different groups of explosive compounds. Combined swabs were spiked with 100ng of explosive.

Introduction

Mass Spectrometry Thermal Desorption (MS-TD) has traditionally been a staple in forensic labs for high-throughput analysis of trace samples. Mass Spec Analytical Ltd. (MSA) now introduces NXT Detect, a revolutionary system that emphasizes portability, a smaller footprint, and ease of use for desktop trace detection with swab sampling. This system can identify a wide range of threats, including explosives, pesticides, drugs, and chemical warfare
simulants, using a novel approach.
NXT Detect offers detection limits in the low nanogram range through direct thermal analysis, with dried swabbed liquid samples on glass slides achieving sensitivities as low as 100ng. However, common interferents such as cleaning products, cosmetics, and oils can pose challenges. Our poster addresses these issues by evaluating the prototype’s tolerance to everyday interferents, showcasing how NXT Detect handles these challenges. This research aims to enhance the applicability and reliability of mass spectrometry trace detection for accessible, real-world deployments in threat detection and forensic analysis.

Methods and Materials

Prototype System Overview:

This study employs a high-throughput prototype system for diverse threat trace analysis, integrating components from Mass Spec Analytical Ltd. (MSA) and Waters Corporation. The system seamlessly combines the MSA Compact Thermal Desorber (TD) Ion Source and the Waters RADIAN ASAP Direct Mass Detector (MS), showcasing advanced trace detection technology.


MSA TD Ion Source:

  • Set to 200°C, 9 L/min flow rate, using PTFE-coated fiberglass swabs for thermal desorption.

Waters RADIAN MS:

  • Robust mass analysis with variable cone voltage, using Waters MassLynxTM software.

Explosive Compound Analysis:

PETN, RDX, TNT detected in negative APCI mode.

Environment Sampling Methodology:

Swabs from 30 locations, 10-second insertion, 90-second interval, check swabs as benchmarks.

Interferant/Suppressant Analysis:

Tested common interferents like WD40, hand sanitiser, cologne, multipurpose cleaners, and body moisturizer.

Results

Environmental Tests:

To evaluate the prototype’s ability to handle background contaminants, over 500 environmental swabs were collected from various locations, including homes, offices, vehicles, and public spaces. Each swab was analyzed following a rigorous protocol:

  • 10-second insertion: Samples were introduced briefly to minimize background contamination.
  • 90-second interval: Sufficient time was allowed for signal baseline recovery between samples.
  • Check swabs: Clean swabs spiked with known explosives were analyzed at regular intervals as a performance benchmark.
    A total of 447 analyses were conducted over a 7-hour period, with check swabs interspersed throughout (Figure 2). The results were encouraging:
  • Minimal performance degradation: Check swabs consistently maintained acceptable detection levels, demonstrating the prototype’s resilience to environmental contaminants.
  • Gradual decline: The slow decrease in sensitivity over time allows for convenient monitoring and proactive intervention.

Extrinsic Residue Suppression:

To gauge the prototype’s resistance to environmental interferences commonly encountered during real-world deployments, eight everyday substances – including colognes, cleaners, and hand sanitizers – were selected for testing.
A standardized approach was employed: residues were applied to glass slides (three per compound) and then swabbed for analysis. This process was followed by transfers from residue slides to evaluate potential carryover effects. To ensure data integrity, samples were run in a predetermined order, interspersed with check swabs analyzed at regular intervals (100 ng RDX) (Figure 3).
Notably, even after analyzing 24 residue samples per experiment, no decline in performance was observed for the explosive check swabs, demonstrating the prototype’s resilience to common environmental contaminants. The procedure was repeated for PETN and TNT, yielding very similar results.

Intrinsic Residue Suppression:

To assess “intrinsic suppression” – where interferents directly hinder explosive detection – five residues were retested individually and combined with each explosive.
Combined swabs were prepared by transferring residue followed by spiking with explosive (100 ng). Three acquisitions were run for each combination: isolated explosive, residue alone, and combined. This process was repeated for RDX, PETN (using furniture polish instead of cleaner), and TNT.
Figure 4 shows that there is an effect of intrinsic suppression on the instrument, however, it is not so detrimental that analysis cannot be conducted. The explosive most affected by intrinsic suppression is the TNT which may be due to its relationship with the chlorine adduct; it is not working in its optimal conditions as the chlorine required to analyse RDX and PETN also has the effect of suppressing the ionisation of the TNT itself.

Real Work Application

This work integrates seamlessly with MSA’s current Scentinel walk-up analysis software suite and SpectralWorks® RemoteAnalyzer®. This simplifies complex data analysis into clear positive/negative results displayed on a user-friendly touchscreen interface. This empowers non-expert personnel, such as security personnel, to take immediate action based on rapid (8-10 seconds) feedback.
The workflow involves a simple four-step process: sample collection, on-screen analysis type selection, swab insertion guided by prompts, and result visualization within seconds. Positive results are clearly distinguishable in red. Additionally, remote data archiving facilitates expert review for trend analysis and future research endeavors.


This approach has been successfully demonstrated for the detection of drugs and
pesticides. The underlying technology possesses significant potential for the analysis of
a wide range of analytes.

Conclusions

Field trials demonstrated the prototype’s environmental robustness, suitable for real-world deployment. Rapid analysis capabilities combined with proactive monitoring features
enhance its field-readiness. Minimal intrinsic background signal ensures reliable detection of target analytes.
This high-performance system exhibits excellent performance in diverse trace detection applications, particularly under challenging environmental conditions.
This research presents a novel trace detection system with promising capabilities for diverse applications, including explosives and chemical warfare agent detection, environmental monitoring, and illicit drug screening.
The system’s user-friendly interface further expands its potential for broad utilisation by personnel with varying levels of technical expertise.