ORBECO SP600, Instruction Manual, Page: 33 / 334

31
SP600 Spectrophotometer 01/2008
1.1 Methods
Notes:
1. Strong alkaline or acidic water samples must be adjusted to approx. pH 7 before
analysis (use 1 mol/l Hydrochloric acid resp. 1 mol/l Sodium hydroxide).
2. If chlorine is known to be present, add one drop of 0.1 mol/l Sodium thiosulfate for each
0.3 mg/l Cl
2
in a one litre water sample.
3. Iron interferes with the test. The interferences will be eliminated as follows:
Determine the amount of total iron present in the water sample. Add an iron standard
solution with the same concentration to the vial (point 1) instead of deionized water to
produce the blank.
4. Conversion:
mg/l NH
4
= mg/l N x 1.29
mg/l NH
3
= mg/l N x 1.22
5. N
NH
4
NH
3