ORBECO SP600, Instruction Manual, Page: 75 / 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 Oxidizing agents (e.g. Chlorine,
Bromine) 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. Turbidity (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.
In this event, the reagent tablet DPD No. 1 High Calcium should be used as an
alternative.
* it is not possible to give exactly values, because the development of
turbidity depends on nature and ingredients of the sample.
5. 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.
6. Oxidizing agents such as Chlorine, Ozone etc. interfere as they react like Chlorine
dioxide.