EN 15477:2009 – Fertilizers – Determination of the water-soluble potassium content
1 Scope
This European Standard specifies a method for the determination of water-soluble potassium, which is applicable to all potassium fertilizers listed in Annex I of the Regulation (EC) No 2003/2003 [3].
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1482-2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample preparation
EN 12944-1:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 1: General terms
EN 12944-2:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 2: Terms relating to fertilizers
EN ISO 3696:1995, Water for analytical laboratory use — Specification and test methods (ISO 3696:1987)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12944-1:1999 and EN 12944-2:1999 apply.
4 Principle
The potassium in the sample to be analyzed is dissolved in water. After eliminating or fixing the substances that might interfere with the quantitative determination, the potassium is precipitated in a slightly alkaline medium in the form of potassium tetraphenylborate.
5 Reagents
5.1 General
Use only reagents of recognized analytical grade and distilled or demineralized water (grade 3 according to EN ISO 3696:1995).
5.2 Formaldehyde , clear formaldehyde solution with a mass fraction of 25 % to 35 % formaldehyde.
5.3 Potassium chloride , p. a.
5.4 Sodium hydroxide solution , c = 10 mol/l.
Care should be taken to ensure that only potassium free sodium hydroxide is used.
5.5 Indicator solution
Dissolve 0,5 g of phenolphthalein in ethanol at 90 % and make the volume up to 100 ml.
5.6 EDTA solution
Dissolve 4 g of the dihydrated disodium salt of ethylenediaminetetraacetic acid in water in a 100 ml graduated flask. Make up the volume and mix.
Store the reagent in a plastics container.
5.7 STPB solution
Dissolve 32,5 g of sodium tetraphenylborate in 480 ml of water, add 2 ml of the sodium hydroxide solution (5.4) and 20 ml of a magnesium chloride solution (100 g of MgCl 2 6H 2 O per litre).
Stir for 15 min and filter through a fine, ashless filter.
Store this reagent in a plastics container.
5.8 Liquid for washing
Dilute 20 ml of the STPB solution (5.7) to 1 000 ml with water.
5.9 Bromine water , saturated bromine solution in water.
6 Apparatus
6.1 Graduated flasks , capacity 1 000 ml.
6.2 Beaker , capacity 250 ml and 600 ml.
6.3 Filter crucibles , porosity 5 µm to 20 µm.
6.4 Oven , regulated at (120 ± 10) °C.
6.5 Desiccator
7 Sampling and sample preparation
Sampling is not part of the method specified in this document. A recommended sampling method is given in EN 1482-1.
Sample preparation shall be carried out in accordance with EN 1482-2. Grinding is recommended for homogeneity reasons.
8 Procedure
8.1 Test portion
Weigh to the nearest 0,001 g 10 g of the prepared sample (5 g for potassium salts with a mass fraction of potassium oxide of more than 50 %). Place this test portion in a 600 ml beaker with approximately 400 ml of water.
Bring to a boil and allow it to boil for 30 min. Cool, transfer quantitatively into a 1 000 ml graduated flask, make up the volume, mix and filter into a dry receiver. Discard the first 50 ml of the filtrate (see 8.6).
EN 15477:2009 – Fertilizers – Determination of the water-soluble potassium content