25c.REMOVAL OF ORGANIC COMPOUNDS FROM FERTILISER EXTRACTS
SCOPE
1. This method defines a procedure for removing organic compounds from fertiliser extracts.
FIELD OF APPLICATION
2. This procedure is applicable to analysing samples of fertilisers extracted by Methods 25a and 25b for which a declaration of total and/or water-soluble element is required.
Note:
The presence of small quantities of organic matter usually does not affect determination by means of atomic absorption spectrometry.
PRINCIPLE
3. The organic compounds in an aliquot proportion of the extract are oxidised with hydrogen peroxide.
REAGENTS
Dilute hydrochloric acid (HCl) solution, about 0.5 M:
4.—4.1 Mix 1 volume of hydrochloric acid (ρ = 1.18 g/ml) with 20 volumes of water.
4.2 Hydrogen peroxide solution (30% H2O2 ρ = 1.11 g/ml), free from trace elements.
APPARATUS
5. Electric hot plate with variable temperature control.
PROCEDURE
6. Take 25 ml of the extract solution obtained by Method 25a or Method 25b and place in a 100 ml beaker. In the case of Method 25b add 5 ml of the dilute hydrochloric acid solution (4.1). Then add 5 ml of the hydrogen peroxide solution (4.2). Cover with a watch glass. Allow oxidation to occur at room temperature for about one hour, then bring gradually to boiling and boil for half an hour. If necessary, add a further 5 ml of the hydrogen peroxide to the solution once it has cooled. Then boil to remove the excess hydrogen peroxide. Allow to cool and transfer quantitatively to a 50 ml volumetric flask and make up to volume. Filter where necessary.
Account should be taken of this dilution when taking aliquot portions and calculating the amount of trace element in the product.