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The Beckman Dissolved Oxygen Analyzer
In the Beckman dissolved oxygen analyzer the conductivity of a flowing sample of water is measured. To this water nitric oxide is added and its conductivity again measured. If the sample contains no oxygen, the conductivity is the same in both measurements, because the nitric oxide does not form an ion with the water but is present simply as a dissolved gas. If the water contains oxygen, some of the nitric oxide is oxidized to form nitrite ion and the conductivity of the second cell becomes higher than that of the first: This increase in conductivity is expressed as dissolved oxygen. Since the constituents of the sample other than oxygen do not oxidize nitric oxide, the instrument is specific for dissolved oxygen. Figure 1 is a flow diagram of the analyzer. The sample passes through the first conductivity cell into the reaction column, where it comes in contact with nitric oxide. It then passes through the second conductivity cell, where the greater conductivity which results from the nitrite ion produced by the dissolved oxygen is measured. In order to eliminate interference from bases and buffer salts in the sample, it is passed through one of a pair of deionizing columns ahead of the first conductivity cell. This part of the process removes such interfering ions as sulfite and permits the determination of any residual oxygen that might be present in a sample of sulfite-treated water.
Chemical Engineer, Niagara Mohawk Power Corp., Buffalo, N. Y.
Tucker, Ross C.
Laboratory Supervisor, Niagara Mohawk Power Corp., Oswego, N. Y.