controlled-odor-mimic-permeation-systems-for-olfactory-training-field

Controlled Odor Mimic Permeation Systems for Olfactory Training and Field Testing

The Controlled Odor Mimic Permeation System (COMPS) was developed to provide a convenient field testing method of odor delivery at controlled and ...

US Naval Research Laboratory

Florida International University

The development of instruments and methods for explosive vapor detection is a continually evolving field of interest. A thorough understanding of the characteristic vapor signatures of explosive material is imperative for the development and testing of new and current detectors. In this research a headspace sampling chamber was designed to contain explosive materials for the controlled, reproducible sampling and characterization of vapors associated with these materials. In a detonation test, the chamber was shown to contain an explosion equivalent to three grams of trinitrotoluene (TNT) without damage to the chamber. The efficacy of the chamber in controlled headspace sampling was evaluated in laboratory tests with bulk explosive materials. Small quantities of TNT, triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) were separately placed in the sampling chamber, and the headspace of each material was analyzed by gas chromatography/mass spectrometry (GC/MS) with online cryogenic trapping to yield characteristic vapor signatures for each explosive compound. Chamber sampling conditions, temperature and sampling time, were varied to demonstrate suitability for precise headspace analysis.

Technical note: Headspace analysis of explosive compounds using a novel sampling chamber.

Hexamethylene triperoxide diamine (HMTD) is an easily synthesized and highly sensitive organic peroxide frequently used as a primary explosive. The vapor pressure of HMTD is very low, impeding vapor detection, especially when compared to other peroxide explosives, such as triacetone triperoxide (TATP) or diacetone diperoxide (DADP). Despite this fact, HMTD has a perceptible odor that could be utilized in the indirect detection of HMTD vapor. Headspace measurements above solid HMTD samples confirm that HMTD readily decomposes under ambient conditions to form highly volatile products that include formic acid, ammonia, trimethylamine and formamides. The presence and quantity of these compounds are affected by storage condition, time, and synthetic method, with synthetic method having the most significant effect on the content of the headspace. A kinetic study of HMTD decomposition in solution indicated a correlation between degradation rate and the presence of decomposition species identified in the headspace, and provided further insight into the mechanism of decomposition. The study provided evidence for a proton assisted decomposition reaction with water, as well as an intramolecular decomposition process facilitated by the presence of water. 

Factors affecting the intramolecular decomposition of hexamethylene triperoxide diamine and implications for detection.

While there is a large body of research on the properties and detection of traditional military high explosives and propellant low explosives, there is a dearth of research on homemade explosive (HME) materials, though they are prevalent today. The safety of working with these materials in the laboratory is the greatest limiting factor preventing HME research. A vapor delivery tool, the Mixed Vapor Generation Device (MV-Gen), was designed to safely contain the individual solid or liquid components that often compose homemade explosives vapor plumes and deliver the mixed component vapors for instrumental sampling and analysis. Within the MV-Gen, each component is separated and only the vapors mix as they are carried through the device by flowing air. The resulting mixed vapor is representative of either mixed explosive material or bulk explosives. Component materials are held in up to four individual, removable vials with vapor concentrations controlled by vial orifice size, temperature, and diluent airflow. The total concentration can be adjusted by altering vial temperature via a thermal water jacket surrounding the entirety of the device, or by adjusting the flow rate of diluent air through the device. The MV-Gen was evaluated first with surrogate compounds, followed by two types of homemade explosives, to include a binary explosive mixture and a peroxide explosive. To evaluate the device, vapors were cold-trapped on an online sampling system and analyzed by gas chromatography/mass spectrometry. It was determined that the device yielded reproducible vapor concentrations of both single and mixed components, and the ratio of these vapors can be easily adjusted to mimic varying forms of homemade explosives.

Mixed Vapor Generation Device for delivery of homemade explosives vapor plumes.

A novel method for the detection of vaporous products was developed utilizing a derivatizing agent collected onto a cryo-cooled gas chromatograph (GC) inlet, with analysis by gas chromatography-mass spectrometry (GC-MS). The technique was applied to the detection of ammonia, which has been difficult to detect at trace levels, particularly in the presence of other chemical interferents, due to its small mass and high volatility. To address this, the ammonia is derivatized in the inlet with butyl chloroformate to produce butyl carbamate, a compound that is retained by GC columns and compatible with standard GC-MS analysis. This method was then used to quantify the ammonia headspace vapor concentration produced from the dissociation of bulk ammonium nitrate as well as from mixtures with aluminum and petroleum jelly, which are fuels commonly used in homemade explosives (HMEs).

Quantitative analysis of vaporous ammonia by online derivatization with gas chromatography - mass spectrometry with applications to ammonium nitrate-based explosives.

In security settings, explosive residues or particles are collected by swiping the object of interest (e.g., luggage or package) with a collection medium, or trap. Particles on the trap are thermally desorbed for detection by ion mobility spectrometry (IMS) or other analyses. A high trap sampling efficiency increases the chance of detection, and is affected by a number of factors. In particular, this work studies the effect of trap re-use on collection efficiency of organic explosives, namely 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazinane (RDX), and correlates this data to quantifiable morphology changes. Collection efficiency was measured by liquid extraction of the traps with detection and quantitation by gas chromatography / mass spectrometry (GC/MS). Using silhouette microscopy for visualization of the trap texture, morphology changes were quantified by several measurements of trap roughness and hairiness, drawing from techniques and metrics used in the textiles industry. Nomex traps were visibly roughened by repeated re-use, and this was correlated with significant improvements in trap collection efficiency (11-57%) depending upon the specific analyte and substrate combination interrogated. Teflon-coated fiberglass (TCFG) traps showed little change with repeated swiping and minimal to no improvement in particle collection efficiency. These results have direct implications for optimizing particle collection traps for use in security settings.

Effect of re-use of surface sampling traps on surface structure and collection efficency for trace explosive residues.

A widely recognized limitation in mammalian olfactory research is the lack of current methods for measuring odor availability (i.e., the quantifiable amount of odor presented and thus available for olfaction) of training or testing materials during behavioral or operational testing. This research utilized an existing technology known as Controlled Odor Mimic Permeation Systems (COMPS) to produce a reproducible, field-appropriate odor delivery method that can be analytically validated and quantified, akin to laboratory-based research methods, such as permeation devices that deliver a stable concentration of a specific chemical vapor for instrumental testing purposes. COMPS were created for 12 compounds across a range of carbon chain lengths and functional groups in such a way to produce similar permeation rates for all compounds. Using detection canines as a model, field-testing was performed to assess the efficacy of the method. Additionally headspace concentrations over time were measured as confirmation of odor availability using either externally sampled internal standard-solid phase microextraction-gas chromatography-mass spectrometry (ESIS-SPME-GC-MS) or collection onto a programmable temperature vaporizing (PTV) GC inlet with MS detection. Finally, lifetime usage was considered. An efficient method for producing and measuring reliable odor availabilities across various chemical functional groups was developed, addressing a noted gap in existing literature that will advance canine and other nonhuman mammal research testing.

A Method for Controlled Odor Delivery in Olfactory Field-Testing.

Potassium chlorate is a powerful oxidizer salt that, when mixed with a fuel source, has been used as a homemade explosive (HME). As an inorganic salt, potassium chlorate has no appreciable vapor pressure under ambient conditions and requires temperatures exceeding 300 °C for decomposition. However, detection of potassium chlorate by trained canines has been demonstrated, implying that it exudes a vapor signature with one or more volatile compounds, although no such species have been confirmed to date. In this work, solid-phase microextraction with a novel on-fiber derivatization reaction was used to interrogate the headspace of several potassium chlorate samples of varying purity, as well as that of related chlorinated salts and explosive mixtures. This analysis showed the presence of few volatile species in the headspace of potassium chlorate other than vaporous chlorine, detected as the derivatized product, chloro-2-propanol. Relative amounts of chloro-2-propanol could be compared between potassium chlorate variants, and could be detected in the presence of other volatile species associated with the fuels.

Headspace analysis of potassium chlorate using on-fiber SPME derivatization coupled with GC/MS.

Operationally-deployed canine detectors are often trained on one or a limited number of materials representing a single target odor, and training frequently occurs using materials of a high purity grade in controlled scenarios with minimal other background odors. Conversely, in the field, canine detectors are expected to generalize and identify variations of the target odor, while discriminating from similar extraneous or background odors. This exemplifies the balance between generalization and discrimination required for effective canine detectors. This research explored the tendency for detection canines to generalize or discriminate between similar odorants. Two groups of related odorants were used in two separate studies; (1) odorants of similar functional groups with differing carbon chains, and (2) odorants of similar carbon chain length but differing functional groups. Within each odorant set, the effect of training was addressed by incrementally increasing the number of odorants each canine was trained to detect. Initially, discrimination increased with increasing molecular dissimilarity in both odorant groups. After further training on additional related odorants, generalization increased across the set of odorants of the same carbon chain length, but there were no significant changes in either generalization or discrimination across the set of odorants of the same functional group. The results suggest that the canines in this study were more likely to generalize across compounds of the same chain length with differing functional group than across compounds of the same functional group, but differing chain lengths. Furthermore, some variation in performance between individual canines indicated that the tendency to generalize differed with experience, breed, and other factors affecting olfaction.

Generalization and Discrimination of Molecularly Similar Odorants in Detection Canines and the Influence of Training.

The canine olfactory system is a highly efficient and intricate tool often exploited by humans for detection for its many attributes, including impressive sensitivity to trace analyte vapors. Canine detectors are often touted as having lower limits of detection, or olfactory detection threshold (ODT), than other field-relevant detection technologies; however, previous attempts to quantify canine ODTs have resulted in reported estimates spanning multiple orders of magnitude, even for the same analyte. A major contributor to these discrepancies is the vapor delivery method used for testing, where losses due to adsorption and dilution are often unaccounted for, and the presence of unattended compounds in the vapor stream due to carryover may go unnoticed. In this research, a trace vapor generator (TV-Gen) was used to deliver quantitatively accurate amounts of vapor reproducibly over time for canine testing. Analyte losses due to adsorption to surfaces in the flow path, dilution in the sniff port at the outlet, and analyte carryover were considered. Computational fluid dynamic (CFD) modeling was used to visualize analyte vapor spread throughout the port. CFD simulations revealed the need for a diffuser to encourage the diffusion of the analyte throughout the port. As a result, the modified vapor generator provides analyte air as a diffuse flow that is evenly distributed through the custom sampling orifice, as opposed to a narrow stream of air at the chosen concentration which exits directly into the environment. Laboratory validations were carried out for three analytes, amyl acetate, 2,4-dinitrotoluene (DNT), and methyl benzoate. A linear response across more than two orders of magnitude vapor concentration range was achieved for all analytes. These efforts will be applied in further research utilizing this TV-Gen vapor delivery system for canine ODT testing, eliminating many quantitative changes seen previously. Graphical abstract.

Article	Year
Technical note: Headspace analysis of explosive compounds using a novel sampling chamber. Forensic science international\| PubMed ID: 25596555	2015
Factors affecting the intramolecular decomposition of hexamethylene triperoxide diamine and implications for detection. Journal of chromatography. A\| PubMed ID: 27207576	2016
Mixed Vapor Generation Device for delivery of homemade explosives vapor plumes. Analytica chimica acta\| PubMed ID: 30327112	2018
Quantitative analysis of vaporous ammonia by online derivatization with gas chromatography - mass spectrometry with applications to ammonium nitrate-based explosives. Talanta\| PubMed ID: 30368302	2019
Effect of re-use of surface sampling traps on surface structure and collection efficency for trace explosive residues. Forensic science international\| PubMed ID: 30844637	2019
A Method for Controlled Odor Delivery in Olfactory Field-Testing. Chemical senses\| PubMed ID: 31115435	2019
Headspace analysis of potassium chlorate using on-fiber SPME derivatization coupled with GC/MS. Talanta\| PubMed ID: 31450483	2019
Generalization and Discrimination of Molecularly Similar Odorants in Detection Canines and the Influence of Training. Behavioural processes\| PubMed ID: 32464153	2020
Quantitative vapor delivery for improved canine threshold testing. Analytical and bioanalytical chemistry\| PubMed ID: 33219448	2021

Lauryn E. DeGreeff

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