Microvolume chemical analysis of atmospheric gases and aerosols
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Earth’s atmosphere is a complex mixture of gases and particles. Literally thousands of different chemical species from both natural and anthropogenic sources are present. These materials partake in a variety of chemical reactions and phase partitioning that have profound impacts on climate, ecology, and human health. Analytical chemistry plays an important role for studying the atmosphere since sensitive and high time resolution measurements are needed to unravel the complex chemical processes occurring. This dissertation describes the application of microvolume techniques for the analysis of gases, particles, and reaction systems of relevance to the atmosphere. These methods have the advantage of being inexpensive and potentially portable. In addition, the low fluid volumes employed are well-suited to analysis in which analyte mass is limited, as is often the case for atmospheric analytes. Chapter 2 describes a passive gas sampling probe based on a regenerated cellulose (RC) microdialysis fiber. The sampling approach was used to detect ammonia in air via fluorescence spectroscopy after derivatization with o-phthaldialdehyde (OPA). The approach was effective for sampling ammonia from air due to the high sampling surface area-to-volume ratio. The limits of detection for ammonia were 0.05 ppm which corresponded to a liquid phase LOD of 4.6 x 10-7 M. As an application of the technology, the ammonia in air at a swine barn facility was determined to be 2.98±0.04 ppm, in good agreement with a reference method. Chapter 3 describes an innovative approach for sampling and analyzing single aerosolized droplets of solution by capillary electrophoresis-laser induced fluorescence (CE-LIF). In the approach, single particles were collected into a droplet formed at the end of a fused silica capillary via inertial impaction. A light scattering pulse was used to signal arrival of a particle and trigger CE separation. At 15 kV, a mixture of FITC - GLU and FITC - GLY could be separated in less than 120 s allowing qualitative analysis of single aerosolized droplets. This method has the potential for liquid phase analysis of single atmospheric aerosol particles. Chapters 4 and 5 describe use of on-line CE for studying aqueous phase atmospheric chemistry. Specifically, I have studied the dynamics of nitration reactions of aromatic compounds. This type of reaction rapidly produces colored products that absorb light at wavelengths above the actinic cut at = 290 nm and therefore may influence absorption of solar radiation and photochemistry. Flow-gated capillary electrophoresis (CE) was coupled with a UV absorbance detector to analyze products of the nitration reactions of benzoic acid and phenol. Inclusion of β-cyclodextrin in the electrophoresis buffer allowed resolution of the ortho-, meta-, and para- nitro- substituted isomers in fewer than 4 min. Sequential separations (online analysis) allowed the reaction kinetics to be quantitatively described. For benzoic acid, product yields were low (2 - 3%), and results suggest both 3- and 2-nitrobenzoic acid form in a 1 - 1.4 concentration ratio. For phenol, the reaction occurred more rapidly with observed yields between ≈10 - 30% for individual isomers. The yield of 2-nitrophenol was higher than 4-nitrophenol by a ratio of ≈ 1.7 – 2, and 3-nitrophenol was not detected. ESI-MS measurements confirmed m/z values of expected reaction products.