All ETDs from UAB

Advisory Committee Chair

Claudiu T Lungu

Advisory Committee Members

Riedar K Oestenstad

Edward M Postlethwaith

Guiseppe L Squadrito

Andrei Stanishevsky

Uday Vaidya

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) School of Public Health

Abstract

Millions of workers are occupationally exposed to volatile organic compounds (VOC) annually, requiring exposure assessments through air sampling. Reducing time to knowledge while maintaining adequate sensitivity and affordability is a constant struggle. Sorbent sampling is the preferred technique for VOC exposure assessments. Chemical desorption of sorbents is the most common desorption technique, but sensitivity is limited due to the small injection fraction. Thermal desorption has excellent sensitivity, but provides only one analysis per sample and is cost prohibitive. The goal of this dissertation was to develop a desorption technique that bridges the sensitivity gap between chemical desorption (0.1%) and thermal desorption (100%) techniques. Carbonaceous sorbents were irradiated with high intensity broad spectrum light to release a preloaded VOC. The first study demonstrates that broad spectrum light can be used to achieve reliable partial desorption. In this study activated carbon powder (AC-p) and single walled carbon nanotube powder (SWNT-p) were preloaded with toluene vapor and partially desorbed by irradiation with a common 50W halogen lamp. When irradiated at the highest lamp setting for four minutes, AC and SWNT-p samples desorbed 45.9% (+/-5.39) and 70.5% (+/- 5.67) respectively. Both materials met method validation criteria of 95% confidence interval within 25% of true mean, but SWNT-p desorption was significantly greater. The second study used high intensity camera flash to desorb AC-p, SWNT-p and SWNT felt (SWNT-f) sorbents pre-loaded with toluene vapor. SWNT-f desorbed significantly greater mass of toluene than AC-p or SWNT-p. A model was constructed to predict desorption which closely agreed with SWNT-f experimental data but not AC-p or SWNT-p. The third study demonstrated that desorption from SWNT-f remains proportional at lower toluene loadings, but AC-p and SWNT-p increases drastically. AC-p and SWNT-p were found to violate two of three model assumptions and were dismissed as candidates for further development for use with photothermal desorption. In summary, highly interconnected sorbents such as SWNT-f are good candidates for photothermal desorption, exhibiting a wide range of desorption (0.001 - 7.7%) depending on the flash energy and number of flashes applied. This facilitates repeated analyses of the same sample at greatly enhanced sensitivity over chemical desorption.

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