Paragraph 4 REAGENTS

Place in a 500 ml volumetric flask containing 300 ml of water:

• — 75 g of ammonium acetate (NH₄OOCCH₃);

• — 10 g of disodium salt of ethylene diamine tetraacetic acid (Na₂EDTA);

• — 40 ml of acetic acid (CH₃COOH, ρ = 1.05 g/ml).

• Make up to volume with water and mix thoroughly. The pH of the solution, checked by means of a glass electrode, must be 4.8 ± 0.1.

Place in a 200 ml volumetric flask

• — 10 ml of the buffer solution (4.1);

• — 400 mg of azomethine-H (C₁₇H₁₂NNaO₈S₂);

• — 2 g of ascorbic acid (C₆H₈O₆).

• Make up to volume and mix thoroughly. Do not prepare large quantities of this reagent as it is stable for only a few days.

Boron stock solution (100 μg/ml)

Boron working solution (10 μg/ml)