Detection of Organic Molecules Dissolved in Water Using a .GAMMA.-Al2O3 Chemiluminescence-Based Sensor
Chemiluminescence measurement is a very useful method for detecting molecules. This method has high sensitivity, good reproducibility and selectivity, quick response and good linearity over a wide concentration region. However, it is not convenient for continuous and long-term detection, because a supply of reactants to produce luminescent species through a chemical reaction is required. Although many investigations have attempted to improve these disadvantages since 1960 1-4 , a long-term
... , a long-term stability of the sensitivity has hardly been attained. A new possibility of a CL-based sensor which does not require a supply of reactants was proposed by Breysse et al. in 1976. 5 They observed CL during the catalytic oxidation of carbon monoxide on a thoria surface. In 1990, we found that CL is observed during the catalytic oxidation of organic vapors on an alumina surface. 7 These phenomena can be applied to CL-based sensors. Various methods to detect organic vapors in air have been reported elsewhere.     In this paper, we deal with a method used to detect organic molecules, e.g. acetone and ethanol, dissolved in water using this sensor. We will describe the elementary working mechanism of the sensor and its working condition under which the response is quick and stable. A new method is proposed for recognizing organic molecules dissolved in water using a chemiluminescence-based sensor made with a γ-Al2O3 catalyst. When a mixture of air and organic molecules, e.g. ethanol and acetone vaporized from a solution, flows around the sensor, chemiluminescence (CL) is emitted during its catalytic oxidation. The CL spectra consist of subbands peaking at the same wavelengths independent of the type of vapors. The peak wavelengths of these subbands are the same as those for CL with a CaCO3 catalyst. The relative CL intensity of each band, however, depends on the type of the vapor and the temperature of the sensor. This implies that CL originates in the same kinds of luminous species produced during the course of catalytic oxidation. By keeping a sample gas around the sensor in a state of laminar flow and by keeping the catalytic oxidation on the sensor under the diffusion-controlled condition, the CL intensity becomes stable and reproducible. The CL intensity is proportional to the concentration of these organic vapors in the gas phase within the concentration range of from 1 -500 ppm.