Solving the impact of sample matrix on trace explosive detection using 3D printed micro-solid phase extraction arrays and high resolution analysis

Lead Research Organisation: King's College London
Department Name: Analytical & Environmental Sciences

Abstract

Interference arising from complex sample matrices can be significant on trace explosives detection, especially when screening for large numbers of structurally diverse compounds. The aim of this project is to characterise, mitigate and/or harness the sample matrix for semi-targeted trace organic explosives detection through the development of solid phase extraction array platforms (SPE) and analysis using liquid chromatography-high resolution mass spectrometry (LC-HRMS).
The first objective is to characterise effects of matrices on analyte recovery across several sorbent combinations using a range of operationally relevant sample matrices e.g. soil, environmental waters, oils and biological fluids. The inter- and intra-sample variance will be assessed as well as interfering ionisation effects in HRMS detection.
The second objective of this project is to miniaturise the optimised sorbent array into a micro-SPE platform.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510531/1 01/10/2016 30/09/2021
1812614 Studentship EP/P510531/1 01/10/2016 30/09/2020 Rachel Irlam
 
Description The detection and identification of trace concentrations of organic explosives from forensically relevant samples is of paramount importance after an explosives-related crime, for example a terrorist attack. This is currently challenging due to problems, termed 'matrix effects', introduced to the analysis by interfering and non-target components of the sample, which are present as well as the explosives of interest. As a result, inaccurate quantitation and/or false negatives can arise, which could lead to miscarriages of justice. Implementation of a technique to clean-up the sample, prior to further instrumental analysis for separation and detection of the target components, can reduce these matrix effects, the most common of which is solid phase extraction (SPE). This work has developed a novel approach to SPE based on combinations of sorbents of different chemistries that, when used together, can effectively remove unwanted compounds from the analysis, whilst simultaneously extracting the target explosives compounds. The performances of the different sorbents were found to be matrix-specific and combinations were optimised for 6 operationally relevant sample types (including soil, swabbed dried blood, swabbed cooking oil, dirt residues and environmental waters), successfully resulting in reduced matrix effects overall and greater sensitivity towards the target explosives compounds (they were detectable at concentrations approximately ten-fold than achieved in previously published methods).
Another difficulty with the analysis of explosives is due to the nature of the compounds themselves. Many of them are prone to rapid degradation and/or evaporation, meaning there is a relatively small window of detection for many of them. Traditional SPE apparatus is cumbersome and requires additional equipment, such as vacuum pumps, both of which restrict its implementation at-scene. In order to overcome this, this work then miniaturised the novel, combined-sorbent SPE approach using 3D printing. 'Clickable', Lego-inspired blocks were designed and printed, which i) could be packed with sorbent without bleed, ii) implemented a standardised thread fitting at the top of the blocks to create a block-to-world interface and allow connection with existing lab equipment, such as pumps, and iii) enabled the delivery of solvent and sample at SPE-relevant flow rates (up to 10 mL/min) without leaking at the inlet or connections between blocks. The sample and solvent delivery could also be pump-assisted or manual, via a handheld syringe, creating the potential for on-site use. This 3D-printed approach proved very successful for the trace detection of explosives, with method performance results comparable to those achieved using commercially available cartridges.
Finally, commercially available materials for 3D printing are limited and their compositions are often proprietary. The final part of this work involved characterisation of the 3D printing resin used throughout the project, as well as investigation into modification of its surface post-build. Successful hydrolysis of the surface functional groups and further coupling with selected compounds of choice was shown to introduce different chemistries, thereby increasing the flexibility of the designed SPE approach and opening new avenues for in-situ sorbent synthesis (hence removal for packing with, and reliance on, commercially available sorbent), as well as application in other fields.
Exploitation Route Firstly, the outcomes of this funding could be put to use by forensic providers working in the analysis and detection of explosives. The work was carried out in close collaboration with the UK's Defence Science and Technology Laboratory (Dstl) to ensure any useful methods developed could be integrated with existing standard procedures.
Secondly, the outcomes of this funding could be put to use by academics, not only for defense and security applications, but also in other fields where (on-site) extraction of trace concentrations of target compounds from complex samples is essential, for example the environmental and food sciences.
Sectors Government, Democracy and Justice,Security and Diplomacy
URL https://www.sciencedirect.com/science/article/pii/S0039914019305314
 
Description Overseas Conference Travel Grant
Amount £350 (GBP)
Organisation Analytical Chemistry Trust Fund of the Royal Society of Chemistry 
Sector Charity/Non Profit
Country United Kingdom
Start 06/2019 
End 06/2019
 
Description Postgraduate Research Funding
Amount £300 (GBP)
Organisation King's College London 
Sector Academic/University
Country United Kingdom
Start 06/2019 
End 06/2019