ORBECO SP600, Instruction Manual, Page: 141 / 334

139
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 Hydrogen peroxide 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 Hydrogen peroxide 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 acid 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 5 mg/l Hydrogen peroxide 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 Hydrogen peroxide. 10 ml of the diluted sample will be mixed with the
reagent and the measurement repeated.
Oxidizing agents such as Chlorine, Ozone etc. interfere as they react like Hydrogen
peroxide.