NBN EN 13650:2001

This European Standard specifies a method for the routine extraction of aqua regia soluble elements (as listed in annex B) from soil improvers or growing media. Materials containing more than about 28 % (m/m) organic matter will require treatment with additional nitric acid. With high solute concentrations in extract solutions, spectral interference's and background enhancement should be expected.
The method is not applicable to liming materials and preformed materials such as mineral wool slabs and foam slabs.
NOTE 1 Aqua regia will not totally dissolve most soil improvers or growing media, and the efficiency of extraction for particular elements differs from element to element. Such efficiency might also differ for the same element in different matrices. Elements extractable in aqua regia cannot therefore, be described as "Totals"; conversely they cannot be regarded as the "bio-available" fraction, as the extraction procedure is too vigorous to represent any biological process.
NOTE 2 The requirements of the standard may differ from the national legal requirements for the declaration of the products concerned.