ORBECO SP600, Instruction Manual, Page: 139 / 334

137
SP600 Spectrophotometer 01/2008
1.1 Methods
Notes:
1. Vial cleaning:
As many household cleaners (e.g. dishwater 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 pH adjustment. Strong alkaline or acidic water
samples must be adjusted to between pH 6 and pH 7 before the reagent is added (use
0.5 mol/l Sulfuric acid resp. 1 mol/l Sodium hydroxide).
4. Exceeding 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 must be diluted with water
free of Bromine. 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.