(617bx) Modeling of Microreactors for Chemoselective Capture of Trace Volatile Organic Compounds

We report a microreactor approach for chemoselective capture of trace carbonyl compounds in air and exhaled breath. The Microreactors were fabricated on silicon wafer by microelectromechanical systems (MEMS) technology. There were thousands of micropillars in the microreactor to distribute gas flowing through the microreactor. The micropillar surfaces were functionalized with a quaternary ammonium aminooxy salt for chemoselective capture of trace carbonyl compounds by means of oximation reactions. 500 mL to 1L gaseous samples with known amounts of carbonyl compounds in Tedlar bags were used for characterization of capture efficiencies. Carbonyl compounds captured by the microreactors were analyzed by Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry (MS). Carbonyl compounds including aldehydes and ketones are ubiquitous in air, exhaled breath, aerosols of electronic cigarette and conventional cigarette smoke. Some carbonyl compounds in exhaled breath are related to disease metabolic processes. Quantitative analysis of trace carbonyl compounds is critical for identification of disease metabolic markers in exhaled breath. One challenge of the microreactor approach was that the capture efficiencies of carbonyl compounds were significantly affected by the gas flow rate. Higher capture efficiencies of carbonyl compounds (95%) require lower sample flow rate, thus longer sample process time. Longer sample process time results in degradation of carbonyl compounds in the sampling bags. This work investigated the effects of the gaps between the micropillars and microreactor length on capture efficiencies of carbonyl compounds at different flow rates. A reaction engineering model was developed to understand the effects of the microreactor length and the gap between the micropillars on the capture efficiencies of carbonyl compounds at different sample flow rate. Breath samples were used to validate the capture efficiencies of the microreactors with different length at various sample flow rates.