spectrophotometric analysis, at l — 522 nm, and the amount of manganate is measured with similar ease, at l — 426 nm. Both ions obey Beer's law up to 100 mg/L.
The first step in the PD test is the introduction of a known amount of MnO— into a sample of the feedwater or a dilution thereof. This mixture is allowed to react in a boiling water bath (100 °C) for 2h. The mixture is cooled in water for 10 min, followed by glass fiber filtration to remove manganate from the sample. The absorbance of the mixture is measured. The procedure is repeated for the permeate stream.
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