1.1 Methods
General:
Ortho-Phosphate ions react with the reagent to form an intense blue colour (methods 320,
323, 324, 325 and 326).
Phosphate in organic and condensed inorganic forms (meta-, pyro- and polyphosphates)
must be converted to ortho-Phosphate ions before analysis.
Pretreatment of the sample with acid and heat provides the conditions for hydrolysis of the
condensed inorganic forms. Organically combined phosphates are converted to ortho-
Phosphate ions by heating with acid and persulfate.
The amount of organically combined phosphates can be calculated:
mg/l Phosphate, organic = mg/l Phosphate, total – mg/l Phosphate, acid hydrolysable
In methods 321 and 327 the ortho-Phosphate ions react with the Vanadate-molybdate-
reagent under acid conditions to form a yellow coloured product.
Notes – only for tube tests and tests with powder packs:
323, 324, 325, 326
1. Application: for water, wastewater and seawater.
2. Highly buffered samples or samples with extreme pH values should be adjusted
between pH 2 and pH 10 before analysis (with 1 mol/l Hydrochloric acid or 1 mol/l
Sodium hydroxide).
3. Interferences:
Large amounts of turbidity may cause inconsistent results.
Interfering substance Interference level:
Aluminium greater than 200 mg/l
Arsenate at any level
Chromium greater than 100 mg/l
Copper greater than 10 mg/l
Iron greater than 100 mg/l
Nickel greater than 300 mg/l
Silica (Silicium dioxide) greater than 50 mg/l
Silicate greater than 10 mg/l
Sulfide at any level
Zinc greater than 80 mg/l
Phosphate, ortho
=
^
Phosphorus, reactive
To Next Page
Loading...
