Thermo Scientific AQUAfast AQ3700, User Manual

Page: 103 / 264

0
Thermo Scientific Orion AQUAfast AQ3700 Colorimeter User Guide
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 demand.
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 color development is carried out at a pH value of 6.2 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 or 1 mol/l Sodium hydroxide,
respectively).
4. Exceeding the measuring range:
Concentrations above 5 mg/l Hydrogen Peroxide can lead to results showing 0 mg/l.
In this event, the water sample must be diluted with water free of Hydrogen Peroxide.
10 ml of the diluted sample should be mixed with the reagent and the measurement
repeated.
Oxidizing agents such as Chlorine, Ozone etc. interfere as they react in the same way
as Hydrogen Peroxide.