Characterization of microreactor and analysis of carbonyl compounds in exhaled breath.

Abstract

Analysis of trace volatile organic compounds at parts per billion (ppbv) to parts per trillion (pptv) level has become an important research frontier because of the applicability for environmental monitoring and noninvasive diagnosis of diseases. The methods of preconcentration for detection of trace aldehydes and ketones both in ambient air and human exhaled breath have increased considerably over the last decade. However, the majority of these methods are not efficient. In this dissertation, we have improved an innovative microreactor that is suitable for quantitative analysis of volatile carbonyl compounds (VOCs) in ambient air as well as in human exhaled breath. The approach is based on microreactor chips fabricated from four inch silicon wafers. The chips have thousands of micropillars in the microfluidic channels for uniformly distributing gaseous samples flowing through the microreactors. The surfaces of the micropillars are functionalized with a quaternary ammonium aminooxy salt 2-(aminooxy)-N,N,N trimethylethanammonium (ATM) iodide for trapping trace ketones and aldehydes by means of oximation reactions. ATM adducts and unreacted ATM are eluted from the microreactor with methanol and directly analyzed by UHPLC-MS. Design and characterization of the microreactors were first investigated. The reaction kinetics of the aminooxy reagent ATM with carbonyl were obtained. A reactor model was established to predicate the relationship between the capture efficiencies of carbonyl compounds and the microreactor length at a given gaseous sample flow rate. The microreactors were then used to study the stability of breath VOCs. VOCs, collected in Tedlar bags, were stable for about two hours with less than 5% of a concentration decrease. Storage of breath samples in a refrigerator reduces the concentration changes of VOCs. The analysis of exhaled breath samples of patients for early lung cancer screening program using the microreactor indicates that C 3 H 6 O, C 2 H 4 O 2 and C 4 H 8 O 2 can serve as biomarkers to distinguish patients with pulmonary nodules from healthy controls. The analysis of exhaled breath samples of the lung cancer (LC) patients, patients with benign pulmonary nodules and healthy controls led to three VOCs (2-butanone, 3-hydroxy-2-butanone and 4-hydroxy-2-nonenal (4-HNE)) as markers for distinguishing LC patients from patients with benign pulmonary nodules and healthy controls. 4-HNE can also be used to distinguish squamous cell carcinoma from adenocarcinoma LC.