Water quality -- Determination of chloride -- Silver nitrate titration with chromate indicator (Mohr's method)

Document Number: NL ISO 9297 : 2009
Sector: Food Technology
TC: No
ICS: 13.060.50
1.1 Application range This International Standard specifies a titration method for the determination of dissolved chloride in water. The method is applicable to the direct determination of dissolved chloride in concentrations between 5 mg/l and 150 mg/l. The working range may be extended to 400 mg/l by using a burette of larger capacity or by sample dilution. Due to many interferences the method is not applicable to heavily polluted waters of low chloride content. 1.2 Interferences Normal concentrations of common constituents of ground water, surface water and potable water do not interfere with the determination. The following substances interfere with the method — Substances forming insoluble silver compounds, such as bromides, iodides, sulfides, cyanides, hexacyanoferrates(ll) and hexacyanoferrates(lll). If necessary, bromide and iodide ions shall be determined separately, and the result of the chloride determination corrected accordingly. — Compounds forming complexes with silver ions, such as ammonium and thiosulfate ions. — Compounds which will reduce Chromate ions, including iron(ll) and sulfite ions. The interferences mentioned above will lead to high chloride values. Highly coloured or turbid solutions may obscure the end point, for example hydrated iron oxide. Table 1 — Interferences Substance Amount interfering mg/l Br− 3 I− 5 S2− 0,8 CN− 1 Fe(CN)64− 2 Fe(CN)e 3− 2 NH4 + 100 S2 O3 2− 200 SO3 2− 70 SCN− 3 CrO4 2 1 000 PO4 3− 25 Table 1 gives a summary of the concentrations of interfering compounds, in milligrams per litre, that give an increase of approximately 2 % in the result when in the presence of 70 mg/l of chloride.