Section 7: Reagents

Strong Acid Solution: Cautiously add 310 ml of concentrated sulphuric acid to 600 ml of distilled water. Cool and dilute to 1 litre.
Ammonium Molybdate Solution: Dissolve 25.0 g of (NH₄)₆Mo₇O₂₄·4H₂0 in 800 ml of distilled water. Carefully add 500 ml of strong acid solution. Cool and dilute to 2 litres. (Very stable.)
Stannous Chloride Solution: Dissolve 2.5 g of fresh SnCl₂·2H₂O in 20 ml of concentrated hydrochloric acid. Warming on a hot plate will aid dissolution. Dilute to 400 ml with distilled water. (Stable for three days at room temperature.)
Acid Wash Solution: Add 20 ml of strong acid solution (H₂SO₄) to 900 ml of distilled water, and dilute to 1 litre. Approximately 6-8 litres are required for one day of continuous sampling.
Stock Solution: Dissolve 4.3943 g of pre-dried (@105°C) KH₂PO₄ in distilled water and dilute to 1 litre.
Soln. = 1000 ppm P; 1 ml = 1 mg P.
Standard Solution: Pipette 100 ml of stock solution (1000 ppm P) and dilute to 1 litre.
Soln. = 100 ppm P; 1 ml = 0.1 mg P.
Working Standard Solutions: Prepare a series of standards by diluting suitable volumes of Standard Solution (100 ppm P) with distilled water. Suggested Standards: 25, 20, 15, 10, 5, 3, 0.5 ppm P.
Ammonium Persulphate: Reagent grade.
NaOH-EDTA Solution: Dissolve 65 g NaOH and 6 g EDTA in distilled water and dilute to 1 litre. (Used to clean autoanalyser system.)

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