Anions in potable waters - Determination of Anions in Natural and Treated Waters - page 495

Potassium carbonate solution—30% w/v. Dissolve 300g of potassium carbonate in
distilled water and make up to 1L.
Potassium thiocyanate solution—0.0115% w/v. Dissolve 0.115g of potassium
thiocyanate in distilled water and make up to 1L.
Sodium nitrite solution. Dissolve 4.14g of sodium nitrite in distilled water and dilute to
200ml (stable for 1 day only).
Sodium chloride solution—6% w/v. Dissolve 60g of sodium chloride in distilled water
and dilute to 1L.
Ammonium iron(III) sulphate reagent. Dissolve 77g of ammonium iron(III) sulphate
(NH 4 Fe(SO 4 ).12H 2 O) in approximately 300ml of distilled water. Add 334ml of
concentrated nitric acid. (sp. gr. 1.42) and make up to 1L. Heat on a hot plate until all
traces of solid dissolve.
Reagents for the determination of free iodide (System B).
Standard iodide solutions. These are exactly the same as those described for system A.
Potassium carbonate solution—30% w/v. Dissolve 300g of potassium carbonate in
water and dilute to 1L.
Sodium nitrite solution—2.07% w/v. Dissolve 4.14g of sodium nitrite in distilled water
and dilute to 200ml (stable for 1 day only).
Sodium chloride solution—2.5% w/v. Dissolve 25g of sodium chloride in distilled
water and dilute to 1L.
Potassium thiocyanate solution—0.0058% w/v. Dissolve 0.058g of potassium
thiocyanate in distilled water and dilute to 1L.
Ammonium iron(III) sulphate reagent. Dissolve 77g of ammonium iron(III) sulphate
(NH 4 Fe(SO 4 ).12H 2 O) in approximately 400ml of distilled water. Add 75ml of
concentrated nitric acid (sp. gr. 1.42) and make up to 1L. Warm until all traces of solid
dissolve.
Sodium oxalate reagent. Dissolve 5g of sodium oxalate in 100ml of 5 vol. % sulphuric
acid (this reagent is toxic).
Apparatus
Centrifuge speed of 50Hz, glass or polypropylene centrifuge tubes of 150ml capacity,
Polystyrene bottles of 30-50ml capacity. AutoAnalyzer system for colorimetric analysis,
eg the Technicon. AutoAnalyzer 1 system with a range expansion facility that was
operated and maintained in accordance with the instructions given in the Operator
Instruction Manual.
Procedure
Wash all glassware and polystyrene containers with concentrated nitric acid and rinse
copiously with distilled water before use. Dispense 1.0ml of 30% w/v potassium
carbonate solution into a 100ml calibrated flask. Make up to 100ml with a water sample
and shake well. Centrifuge the resulting solution for 5min at 50Hz. Decant about half of
the solution into polystyrene bottles. Allow fresh tap water to stabilise for 3 days before
analysis.
Set up the manifold system shown in the flow diagram (Fig. 7.8) and use the
appropriate set of reagents for either total inorganic iodine determination (A) or free