Wet+Digestion+of+Plant+Samples

Back to Main 1. 2-5 g of dry plant sample material is weighed into a Teflon-tube (2a) or Kjeldahl's flask (2b). The exact mass of the sample is recorded.

2a. The sample is digested with MARS5TM-microwave machine according the introductions given in the manual. 20 ml of aqua regia (3:1 conc. HCl - HNO 3 ) and 0.2-0.5 Bq of 209 Po tracer solution (t½ = 10 3 a) is added to the tube and left to stand for overnight. Write down the activity concentration and the volume of the tracer. After digestion the sample is moved into a decanter glass and the teflon-tube is rinsed with 3 x 2 ml of conc. HCl. Add 15 ml of conc. HCl and evaporate to 2-3 ml and leave cool down.

2b. Alternatively the digestion can be carried out in 500 ml Kjeldahl's flask in concentrated HNO 3 and HCl. First add 50 ml of conc. HNO 3 and start heating carefully, because vigorous foaming may appear in the beginning. The digestion is continued until the HNO 3 solution is evaporated to 10 ml. (If there still is unburned fat etc. HNO 3 can be added and the digestion continued.) Let the flask cool well and add 20 ml of conc. HCl and evaporate HNO 3 away (brown gases disappear). The sample is evaporated to 2-3 ml and left to cool down.