Paragraph 4 REAGENTS
Concentrated nitric acid (ρ = 1.40 g/ml).
Molybdate reagent:
Preparation of the reagent based on sodium molybdate
Solution A: dissolve 70 g sodium molybdate dihydrate in 100 ml water.
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Solution B: dissolve 60 g citric acid monohydrate in 100 ml water and 85 ml concentrated nitric acid (4.1).
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Solution C: stir solution A into solution B to obtain solution C.
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Solution D: to 50 ml water add 25 ml concentrated nitric acid (4.1), add 5 ml freshly distilled quinoline. Add this solution to solution C, mix thoroughly and leave standing overnight in the dark. Make up to 500 ml with water, mix again and filter through a sintered glass funnel (5.3).
Preparation of the reagent based on ammonium molybdate
Solution A: dissolve 100 g ammonium molybdate in 300 ml water, heating gently and stirring from time to time.
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Solution B: dissolve 120 g citric acid monohydrate in 200 ml water and add 170 ml of concentrated nitric acid (4.1).
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Solution C: add 10 ml freshly distilled quinoline to 70 ml of concentrated nitric acid (4.1).
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Solution D: slowly pour, stirring well, solution A into solution B. After thoroughly mixing, add solution C to this mixture and make up to 1 litre with water. Leave standing for two days in a dark place and filter through a sintered glass funnel (5.3).
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The reagents 4.2.1 and 4.2.2 can be used in the same way; both must be kept in the dark in stoppered polyethylene bottles.