4.1.Preparation of sampleU.K.
Place 20 ml of the sample in a platinum dish and evaporate to dryness over a boiling waterbath. Ash in the furnace at 500 to 525 °C. Moisten the white ash with 1 ml of concentrated nitric acid (3.2). Evaporate over a boiling waterbath, repeat the addition of 1 ml nitric acid (3.2) and evaporate a second time. Add 5 ml of dilute nitric acid (3.3) and heat slightly until dissolved.