Plant Aldehyde Measured - C&EN Global Enterprise (ACS Publications)

Nov 6, 2010 - When a basic fuchsin solution reacts with sulfurous acid, explains Mr. Weiss, its intense reel color disappears. The result is Schiff's ...
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Plant Aldehyde Measured Plant analyzer uses SchifFs test to change conductivity, measure acetaldehyde

1 3 6 ACS NATIONAL MEETING Industrial and Engineering Chemistry

Using a change* in conductivity to measure acetaldehyde concentration ol 0 to 1.2' ι in an aqueous stream is an­ other example ol taking the laboratory to the plant. Here it's a chemical re­ action . Schiff's test for aldehydes is the re­ action, Union Carbide Olefins' M. D. Weiss and I. A. Capuano told the Divi­ sion ol Industrial and Engineering Chemistry in a s\mposium on applica­ tions ol new analytical techniques to process control. T h e test is usually used in the lab to determine aldehydes colorimetrically. T h e plant instrument, however, measures the change in elec­ trical conductance from sulfurons acid formed in the reaction. When a basic fuchsin solution reacts with sulfurons acid, explains Mr. Weiss, its intense reel color disappears. The result is Schiff's reagent, which, ho says, involves the forming of leueosulfonic acid and the addition of sulfur dioxide to two amino groups. When this then reacts with an aldehyde, sulfurons acid is given off and a new colored com­ pound forms. Heart of the analyzer is a Lucite conductivity cell with platinized elec­ trodes. T h e cell contains an inlet, an outlet, and a vent to get rid of any trapped gas bubbles. Reagent passes through a reference conductivity cell and into a mixing chamber. Here it reacts with the acetaldehyde sample, and the result­ ing solution goes to the measuring cell. Metering pumps keep Hows of sample and reagent in the sampling system con­ stant. Signals from the cells go to an a.c. conductivity bridge; output from the bridge goes to a recorder. Differential measurement of conduc­ tivity, says Mr. Weiss, is a good general method for converting laboratory tech­ niques to continuous control analyzers. Most lab organic analyses, he adds, result in sonic change in conductivitv.

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