ORBECO SP600, Instruction Manual, Page: 241 / 334

239
SP600 Spectrophotometer 01/2008
1.1 Methods
11. Press ZERO key (blank is already placed in the sample
chamber – see point 8).
Wait for a
reaction period of 2 minutes
.
After the reaction period is finished the zero-reading
starts automatically.
12. Remove the vial from the sample chamber.
13. Place the vial (the sample) in the sample chamber ma-
king sure that the marks are aligned.
14. Press TEST key.
The result is shown in the display in mg/l Silica.
Notes:
1. Close the vials with the cap directly after adding the Vario Molybdate 3 reagent solution,
otherwise it can result in minimum findings.
2. The given reaction time of 4 minutes refers to a water sample temperature of 20°C.
At 30°C a reaction time of 2 minutes, at 10°C a reaction time of 8 minutes is required.
3. The given reaction time of 1 minute refers to a water sample temperature of 20°C.
At 30°C a reaction time of 30 seconds, at 10°C a reaction time of 2 minutes is required.
4. Interferences:
Substance Interference
Iron large amounts interfere
Phosphate does not interfere at concentrations less than 50 mg/l PO
4
at 60 mg/l PO
4
the interference is approx. – 2%
at 75 mg/l PO
4
the interference is approx. – 11 %
Sulfide interfere at all levels
Occasionally water samples contain silica forms which reacts very slowly with Molybdate.
The nature of these forms is not known.
A pre-treatment with Sodium hydrogencarbonate and then with Sulfuric Acid will make
these forms reactive to Molybdate (pre-treatment is given in “Standard methods
for the Examination of Water and Wastewater” under “Silica-Digestion with Sodium
Bicarbonate”).
5. SiO
2
Si
Countdown
2:00
prepare Zero
press ZERO
Zero accepted
prepare Test
press TEST