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Title:Colorimetric sensor arrays with a pre-oxidation method for gaseous analytes
Author(s):Jang, Minseok
Director of Research:Suslick, Kenneth S.
Doctoral Committee Chair(s):Kenneth S. Suslick
Doctoral Committee Member(s):Murphy, Catherine J.; McCall, Benjamin J.; Bailey, Ryan C.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Gas Sensor
Colorimetric Sensor Array
Toxic Pollutants
Abstract:The Suslick group has developed a disposable colorimetric sensor array methodology for use as an optoelectronic nose that has been applied successfully for the identification of a wide range of both gases/vapors and analytes in aqueous liquids. These colorimetric sensor arrays, however, are extremely effective for detecting reactive species, they do not exhibit high sensitivity to less-reactive vapors. Common volatile organic compounds (e.g., aromatic hydrocarbons, chlorocarbons) which are commonly found indoor are not especially reactive and are difficult to detect at low concentration by our colorimetric sensor array. To improve the array response, a disposable pre-oxidation technique has been developed in which a vapor stream is passed through an oxidation tube in front of the array. Oxidation byproducts (e.g., carboxylic acids, phenols, aldehydes, etc.) are reactive species that can be easily detected. Since each analyte produces different kinds of oxidation byproducts, the array gives a unique signature for a wide range of VOCs. The identification and discrimination of the most commonly found indoor pollutants is achieved at various concentrations, including their immediately dangerous to life or health (IDLH), permissible exposure limit (PEL), and 20% of the PEL concentrations. The array with the pre-oxidation has shown excellent performance in the presence of humidity, shelf-life, and reproducibility. Our array with a pre-oxidation method has shown excellent sensitivity and selectivity towards VOCs and indoor pollutants. However, as we have shown in our previous studies, detection of alcohols (e.g., ethanol, methanol, and phenol) with the pre-oxidation tube has not shown excellent sensitivity compared to other VOCs. Alcohols or their oxidation byproducts adsorption on the surface of silica decreased the sensitivity for detection of alcohols. The optimum array response to alcohols occurred with pre-oxidation tubes loaded with 30mg of chromic acid on alumina. Five different alcohols can be successfully detected and discriminated at their IDLH, PEL, and 20% of PEL concentrations. Comparison of the limits of detection of the array for alcohols with the alumina and silica pre-oxidation methods indicated an improvement of ~42-fold. Colorimetric sensor array with the pre-oxidation technique has been applied successfully for detection and discrimination of different brands and grades of automotive fuels and different ignitable liquid residues. Classification analysis reveals that the colorimetric sensor array has an extremely high dimensionality with the consequent ability to discriminate among a large number of similar gasoline and diesel at two different concentrations. The unburned substrates with the selected different accelerants and the burned residues with selected different accelerants can be detected and well discriminated with our array with the pre-oxidation technique. This work demonstrated that our technology can be used for quality control of automotive fuels and fire investigation to indicate the presence of the ignitable liquids. A pre-oxidation spot have been developed as we transition to a linear array since the pre-oxidation tube will be difficult to incorporate. An inorganic formulation consisting of Ludox colloidal silica was successfully developed for printing the strong oxidizing agent. The pre-oxidation spot coated inside the glass tube achieved the equivalent oxidizing power as the pre-oxidation tube, but response times were slower. A linear array was successfully printed and tested, but further work is needed to improve its performance.
Issue Date:2013-02-03
Rights Information:Copyright 2012 Minseok Jang
Date Available in IDEALS:2013-02-03
Date Deposited:2012-12

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