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Chapter 5
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Orion AQUAfast Reagent Chemistry Instructions for Orion AquaMate
Thermo Scientific
Orion AquaMate Spectrophotometer User Manual
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65
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The DPD color development is carried out at a pH value of 6.2 to 6.5. The reagents
therefore contain a buffer for the pH adjustment. Strong alkaline or acidic water samples
must be adjusted between pH 6 and pH 7 before the reagent is added (use 0.5 mol/l
sulfuric acid or 1 mol/l sodium hydroxide).
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Exceeding the measuring range: Concentrations above 10 mg/l chlorine using tablets can
lead to results showing 0 mg/l. In this event, the water sample must be diluted with water
free of chlorine. 10 ml of the diluted sample should be mixed with the reagent and the
measurement repeated.
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Turbidity can lead to errors. The use of the DPD No. 1 tablet in samples with high calcium
ion contents and/or high conductivity can lead to turbidity of the sample and therefore
incorrect measurements.
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Oxidizing agents such as bromine or ozone interfere as they react in the same way as
chlorine.