ORBECO SP600, Instruction Manual, Page: 215 / 334

213
SP600 Spectrophotometer 01/2008
1.1 Methods
General:
Ortho-Phosphate ions react with the reagent to a intense blue colour (methods
317
,
318
,
320 , 323 , 324 , 325 , 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 head 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 method 321 and 322 the ortho-Phosphate ions react with the Vanadate-molybdate-
reagent under acid conditions to a yellow colored 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