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ISO 7890-3

1st Edition, January 1, 1988

Complete Document

Water Quality - Determination of Nitrate - Part 3: Spectrometric Method Using Sulfosalicylic Acid

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ENGLISH * SAME AS BS 6068 P2 S2.36
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Description / Abstract:

Substance determined

This part of IS0 7890 specifies a method for the determination of nitrate ion in water.

Type of sample

The method is suitable for application to raw and potable water samples.


Up to a nitrate nitrogen concentration, @N of O,2 mg/l using the maximum test portion volume of 25 ml. The range can be extended upwards by taking smaller test portions.

Limit of detectionl)

Using cells of optical path length 40 mm and a 25 ml test portion volume the limit of detection lies within the range @N = 0,003 to 0,013 mg/l.


A nitrate nitrogen concentration of @N = 0,2 mg/l gives an absorbance of about 0,68 unit, using a 25 ml test portion and cells of optical path length 40 mm.


A range of substances often encountered in water samples has been tested for possible intetference with this method. Full details are given in annex A. The main potential interferents are chloride, orthophosphate, magnesium and manganese(ll), as shown in annex A.

Other tests have shown that this method will tolerate a sample colour of up to 150 mg/l Pt providing the test portion absorption correction procedure is followed. (See 6.5.)

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