EN 15478:2009 – Fertilizers – Determination of total nitrogen in urea
1 Scope
This European Standard specifies a method for the determination of total nitrogen in urea. This method is applied exclusively to urea fertilizers which are nitrate free.
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
Urea is transformed quantitatively into ammonia by boiling in the presence of sulfuric acid. The ammonia thus obtained is distilled from an alkaline medium, the distillate being collected in an excess of standard sulfuric acid. The excess acid is titrated by means of a standard alkaline solution.
5 Reagents
5.1 General
Use only reagents of recognized analytical grade and distilled or demineralized water, free from carbon dioxide and all nitrogenous compounds (grade 3 according to EN ISO 3696:1995).
5.2 Kjeldahl tablets,
5 g/tablet containing 100 parts K 2 SO 4 to 1 part selenium.
5.3 Sulfuric acid , concentrated ( ρ 20 = 1,84 g/ml).
5.4 Sodium hydroxide solution , approximately NaOH 500 g/l.
5.5 Sulfuric acid , c = 0,05 mol/l, to use for the blank test.
5.6 Sodium or potassium hydroxide solution , carbonate free, c = 0,1 mol/l, to use for the blank test.
5.7 Sulfuric acid, c = 0,5 mol/l.
5.8 Sodium or potassium hydroxide solution , carbonate free, c = 1,0 mol/l.
5.9 Indicator solutions
5.9.1 Mixed indicator
Solution A: Dissolve 1 g of methyl red in 37 ml of 0,1 mol/l sodium hydroxide solution and make up to one litre with water.
Solution B: Dissolve 1 g of methylene blue in water and make up to one litre.
Mix one volume of A with two volumes of B.
This indicator is violet in an acid solution, grey in a neutral solution and green in an alkaline solution; use 0,5 ml (10 drops).
5.9.2 Methyl red indicator solution
Dissolve 0,1 g of methyl red in 50 ml of 95 % ethanol and make up to 100 ml with water. Filter if necessary.
This indicator (4 or 5 drops) may be used instead of the preceding one. This indicator is red in acid solution and yellow in alkaline solution.
5.10 Anti-bump granules , for example pumice stone, washed in hydrochloric acid and calcined.
EN 15478:2009 – Fertilizers – Determination of total nitrogen in urea