An investigation has been made into the accuracy of ammonium-selective (ammonium-responsive) glass electrodes for determining ammonia (10 to 1000 pgl-l) in boiler feed-water and similar high-purity water samples from power stations. The electrode potential follows the Nernst equation in samples containing up to 10 000 mg 1-1 of ammonia, the pH of which is controlled between 8.0 and 8.4 by the addition of triethanolaminehydrochloric acid buffer solution. However, interfering species in the buffer solution cause a detectable deviation from Nernstian response at low ammonia concentrations (less than 1000 pg 1-1). By use of a calomel -0.1 N hydrochloric acid reference electrode, reproducible results have been obtained in static buffered solutions containing 10 to 1000 pgl-1 of ammonia. Of the other impurities likely to be present in power-station waters only sodium caused a serious effect (100 pgl-1 of sodium is equivalent to 25 pg1-1 of ammonia). The within-batch standard deviations of analytical results were 2, 7, 17 and 33 t concentrations of 10, 100, 500 and 1000 pg 1-1 of ammonia, respect-&: &. aDetails of a recommended analytical procedure for discrete samples are given, and the application of the ammonium-selective electrode to continuous on-stream analysis is briefly discussed.* The term "static" refers throughout this paper t o the system in which the electrodes are immersed in a magnetically stirred, buffered solution of the sample contained in a polythene beaker.
A simple, fast method for determining low concentrations of oxygen in power-station waters has been developed, based on the reaction of dissolved oxygen with the leuco-base of methylene blue to give a soluble blue oxidation product the absorbance of which is a function of the oxygen concentration.A special glass cell has been devised, which acts sequentially as a samplecollection vessel, a reaction vessel and a spectrophotometric cuvette. The cell design permits the easy addition of the leuco-base and also the airsaturated water used for calibration. A novel technique of "zero-time extrapolation" for the determination of the reagent/cuvette blank circumvents the difficulty of making this measurement with oxygen-free water.The calibration graph is linear up to 50 pgl-l, but satisfactory measuretnents may be made up to 100 pg 1-l. The criterion of detection is approximately 1.0 pg 1-l with standard deviations ranging between 0.4 and 1 . 7 pg l-l, depending on the concentration. The analysis time is 5-10 min for a single determination.Iron(I1) and copper(I1) ions are the only ions likely to be present in boiler waters that cause serious interference and these must be removed before analysis by passing the water sample through a cation-e:.;changc column.
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