ORBECO SP600, Instruction Manual, Page: 77 / 334

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SP600 Spectrophotometer 01/2008
1.1 Methods
Notes:
1. Vial cleaning:
As many household cleaners (e.g. dishwasher detergent) contain reducing
substances, the subsequent determination of Chlorine dioxide may show lower
results. To avoid any measurement errors, only use glassware free of Chlorine
consumption.
Preparation: Put all applicable glassware into Sodium hypochlorite solution
(0.1 g/l) for one hour, then rinse all glassware thoroughly with deionized water.
2. Preparing the sample:
When preparing the sample, the escape of Chlorine dioxide gases, e.g. by
pipetting or shaking, must be avoided. The analysis must take place immediately
after taking the sample.
3. The DPD colour development is carried out at a pH value of 6.3 to 6.5. The
reagent tablet therefore contains a buffer for the pH adjustment.
Strong alkaline or acidic water samples must be adjusted between pH 6 and
pH 7 before the tablet is added (use 0.5 mol/l Sulfuric acid resp. 1 mol/l Sodium
hydroxide).
4. Exceeding of the measuring range:
Concentrations above 19 mg/l Chlorine dioxide can produce results within the
measuring range up to 0 mg/l. In this event, the water sample must be diluted with
water free of Chlorine dioxide. 10 ml of the diluted sample will be mixed with the
reagent and the measurement repeated.
5. If ??? is displayed at a differentiated test result see page 325.
Oxidizing agents such as Chlorine, Ozone etc. interfere as they react like Chlorine
dioxide.