Indirect Detection of Explosive Vapours by Thermal Dissociation Cavity Ring-Down Spectroscopy

This thesis describes two explosive detection methods capable of detecting explosives indirectly in ambient air. The first of the explosive detection methods utilizes a platinum catalyst heated to 350 °C to catalyze the thermal dissociation of nitroaromatic explosives, such as 2,4,6 trinitrotolune (TNT), to NO2 prior to detection. The catalytic thermal dissociation (cTD) CRDS was found to have a (1s, 3σ) limit of detection (LOD) of 0.5 ppbv. The LOD was sufficient for the detection of TNT in ambient air but lacked the sensitivity to detect less volatile nitro aromatic explosives such as 2,4,6 trinitrophenylmethylnitramine (Tetryl). Efforts to improve the sensitivity of the instrument via a trap and purge pre-concentration scheme were of limited success largely due to poor sample recoveries from the Tenax traps used. The second explosive detection technique exploited radicals generated during the thermal decomposition of triacetone triperoxide (TATP), a peroxide explosive, for detection. These radicals were amplified via a peroxide radical chemical amplification scheme (PERCA) that required the addition of NO and a radical chain carrier, commonly CO, to generate NO2. A modelling study was conducted to assess alternative radical chain carriers as well as the effect of TD on amplification chemistry. Dimethyl ether and ethane were found to be appropriate chain carriers. Additionally, the modelling study suggested that elevated TD temperatures slow down radical chemistry and reduce chemical amplification (CL) while reducing the dependence of CL on relative humidity and radical sinks. A TD-PERCA-CRDS instrument was constructed and its temperature dependent chain length calibrated using peroxyacyl nitrates and peroxy nitric acid. The TD-PERCA-CRDS was found to have a CL up to 69±5 at 250 °C and an LOD (1s, 1σ) of 1.3 pptv. The instrument’s relative humidity dependence was reduced compared to that of room temperature PERCA but the instrument was found to suffer from an ozone interference at temperatures greater than 150 °C. A sample of TATP was synthesized in the lab and its identity and purity established using FTIR. TATP decomposition resulted in an NO2 signal that was 22±3 times larger than that expected from TATP saturation vapour pressure, and the LOD was 5 pptv.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Chemistry

Grantor dc:publisher.institution

Graduate Studies

Year dc:date.issued

2018

Author dc:creator

• Taha, Youssef Mohamad

Advisor dc:contributor.advisor

• Osthoff, Hans D.

Committee members dc:contributor.committeemember

• Shi, Yujun
• Thurbide, Kevin B.
• Kim, Seonghwan
• Hastie, Donald R.

• Chemistry
• explosive
• CRDS
• cavity ring-down spectroscopy
• spectroscopy
• TATP
• TNT

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

eng

DOI

http://dx.doi.org/10.11575/PRISM/31780

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:1880/106492