ORBECO SP600, Instruction Manual, Page: 53 / 334

51
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 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. For individual testing of free and total Chlorine, the use of different sets of
glassware is recommend (EN ISO 7393-2, 5.3)
3. Preparing the sample:
When preparing the sample, the escape of Chlorine gases, e.g. by pipetting or
shaking, must be avoided. The analysis must take place immediately after taking
the sample.
4. The DPD colour development is carried out at a pH value of 6.3 to 6.5. The reagents
therefore contain a buffer for the pH adjustment.
Strong alkaline or acidic water samples must be adjusted between pH 6 and pH 7
before the reagent is added (use 0.5 mol/l Sulfuric acid resp. 1 mol/l Sodium hydroxide).
5. Exceeding of the measuring range:
Concentrations above
10 mg/l Chlorine using tablets
4 mg/l Chlorine using liquid reagents
2 mg/l using powder packs
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. 10 ml of the diluted
sample will be mixed with the reagent and the measurement repeated.
6. Turbidity (lead to errors):
The use of the DPD No. 1 tablet (method 98, 99, 100) 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. Even if the turbidity does occur after the
DPD No. 3 tablet has been added, this can be prevented by using the DPD No. 1
HIGH CALCIUM tablet.
* it is not possible to give exactly values, because the development of
turbidity depends on nature and ingredients of the sample.
7. If ??? is displayed at a differenciated test result see page 325.
Oxidizing agents such as Bromine, Ozone etc. interfere as they react like Chlorine.