1.1 Methods
Notes:
1. Extremely basic or acidic water samples should be adjusted with 0.5 mol/l (1 N) Sulfuric
acid solution or 1 mol/l (1 N) Sodium hydroxide solution to pH 7.
2. Interferences:
Interfering substance Interference levels and treatments
Calcium greater than 1000 mg/l CaCO
3
Iron Interferes at all levels. Correct as follows:
a) determine the concentration of iron present in the
sample by performing a total Iron test
b) add the same iron concentration as determined
to the deionised water (step 1).
The interference will be blanked out successfully.
Magnesium greater than 6000 mg/l CaCO
3
Nitrate greater than 100 mg/l NO
3
-N
Nitrite greater than 12 mg/l NO
2
-N
Phosphate greater than 100 mg/l PO
4
-P
Sulfate greater than 300 mg/l SO
4
Sulfide intensifies the colour
Glycine, Hydrazine,
Colour, Turbidity
Less common interferences such as Hydrazine and
Glycine will cause intensified colours in the prepared
sample. Turbidity and colour will give erroneous high
values. Samples with severe interferences require
distillation.
3.
N
NH
4
NH
3
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