A method of measuring the concentration of a selected organic compound (analyte) in a sample of water involves (1) producing hydrogen peroxide as a byproduct of enzyme-catalyzed oxidation of the analyte, (2) producing light in an electrocatalyzed reaction of the hydrogen peroxide with luminol, and (3) measuring the intensity of this light. The method could prove useful in a variety of applications, including water-purification systems, closed environmental life-support systems, bioreactors, and other biotechnological systems.
The luminescent reaction is effected by feeding two aqueous streams into an electrocatalyzed-luminescence (ECL) cell (see figure). One stream carries luminol dissolved from a bed of luminol crystals. The rate of dissolution of luminol from the bed and the concentration of luminol in the water is maintained at the desired level by maintaining the pH of the water at 10.3; for this purpose, the flow of water is directed through basification modules containing MgO, both upstream and downstream of the luminol bed. (Rebasification downstream of the luminol bed is necessary because the dissolution of luminol neutralizes the solution.)
The other aqueous stream that flows into the ECL cell contains the analyte. If the analyte is H2O2, then this stream is fed directly to the ECL cell without further treatment. If the analyte is an organic compound or compounds, then this stream is first passed through a column containing an immobilized enzyme that catalyzes the oxidation of the analyte. For example, if the analyte is ethanol, then the enzyme is alcohol oxidase. The effluent from the column thus contains the products of the enzyme-catalyzed oxidation, including H2O2.
The two streams are mixed in the ECL cell. A controlled voltage across the cell catalyzes the oxidation of the luminol by hydrogen peroxide from the sample stream. A photomultiplier measures light emitted by this reaction. The intensity of this light is approximately proportional to the concentration of the analyte in the sample.
Light Is Produced in the electrocatalyzed reaction between (a) luminol and (b) H2O2, which is introduced into the sample stream by the enzyme-catalyzed oxidation of the analyte. The amount of light emitted is approximately proportional to the concentration of the analyte in the sample stream.
This work was done by Charles E. Verostko of Johnson Space Center and James E. Atwater, James R. Akse, Jeffrey DeHart, and Richard R. Wheeler, Jr., of Umpqua Research Co. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com under the Life Sciences category, or circle no. 111 on the TSP Order card in this issue to receive a copy by mail ($5 charge).
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Johnson Space Center; (713) 483-4871. Refer to MSC-22605.