This document specifies a method for the determination of free chlorine and total chlorine in water,
readily applicable to lab- and field-testing. It is based on measurement of the absorption, the red DPD
colour complex in a photometer or the colour intensity by visual comparison of the colour with a scale
of standards that is regularly calibrated.
This method is appropriate for drinking water and other waters, where additional halogens like
bromine, iodine and other oxidizing agents are present in almost negligible amounts. Seawater and
waters containing bromides and iodides comprise a group for which special procedures are to be
carried out.
This method is in practice applicable to concentrations, in terms of chlorine (Cl2), from, for example,
0,000 4 mmol/l to 0,07 mmol/l (e.g. 0,03 mg/l to 5 mg/l) total chlorine. For higher concentrations, the
test portion is diluted.
Commonly, the method is applied as a field method with mobile photometers and commercially available
ready-for-use reagents (liquid reagents, powders and tablets). It is essential that those reagents comply
with minimum requirements and contain the essential reagents and a buffer system suitable to adjust
the measurement solution to a pH range of typically 6,2 to 6,5. If there is doubt that water samples
have uncommon pH values and/or buffer capacities, the user has to check and, if necessary, to adjust
the sample pH to the required range. The pH of the sample is within the range of pH 4 and 8. Adjust, if
necessary, with sodium hydroxide solution or sulfuric acid before the test.
A procedure for the differentiation of combined chlorine of the monochloramine type, combined
chlorine of the dichloramine type and combined chlorine in the form of nitrogen trichloride is
presented in Annex A. In Annex C, a procedure is presented for the determination of free and total
chlorine in drinking and other low polluted waters, for disposable planar reagent-filled cuvettes using a
mesofluidic channel pump/colorimeter.
Required fields are indicated with *
