BS EN 13650:2001 – Soil improvers and growing media — Extraction of aqua regia soluble elements
1 Scope 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.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
EN ISO 3696, Water for analytical laboratory use – Specification and test methods (ISO 3696:1987).
EN 13039, Soil improvers and growing media – Determination of organic matter content and ash.
EN 13040:1999, Soil improvers and growing media – Sample preparation for chemical and physical tests,determination of dry matter content, moisture content and laboratory compacted bulk density.
3 Terms and definitions
For the purposes of this standard the terms and definitions given in EN 13039 and EN 13040 apply.
4 Principle
The dried sample is finely ground and extracted with a hydrochloric/nitric acid mixture by standing for 16 h at room temperature, followed by boiling under reflux for 2 h. The extract is clarified and the extracted elements determined.
The test sample shall be ground to less than 500 m prior to aqua regia digestion. Such grinding is designed to
a) give a more homogeneous sample from which a sub-sample is taken;
b) increase the efficiency of acid attack by increasing the surface area of the particles.
5 Reagents
5.1 General
All reagents used shall be of recognized analytical quality. Use water of grade 2 complying with EN ISO 3696.
Deionized water may be used, providing that it meets the requirements given above. It is recommended that the same batch of water be used throughout a given batch of determinations and that blank determinations are carried out.
5.2 Hydrochloric acid, c(HCl) = 12 mol/l; 1,18 g/ml; 37 % mass/volume.
5.3 Nitric acid, c(HNO 3 ) = 15 mol/l; 1,42 g/ml; not less than 65 % mass/volume.
5.4 Nitric acid, c(HNO 3 ) = 0,5 mol/l, 35 ml nitric acid (5.3) is diluted to one litre of water.
BS EN 13650:2001 – Soil improvers and growing media — Extraction of aqua regia soluble elements