EN 15558:2009 – Fertilizers – Determination of nitric and ammoniacal nitrogen according to Ulsch
1 Scope
This European Standard specifies a method for the determination of nitrate and ammoniacal nitrogen with reduction according to Ulsch.
The method is applicable to all nitrogenous fertilizers, including compound fertilizers, in which nitrogen is found exclusively in nitrate form, or in ammoniacal and nitrate form.
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
Reduction of nitrates and nitrites to ammonia by means of metallic iron in an acid medium and displacement of the ammonia thus formed by the addition of an excess of sodium hydroxide: distillation of the ammonia and determination of the yield of ammonia in a known volume of standard sulfuric acid solution and titration of the excess sulfuric acid by means of a standard solution of sodium or potassium hydroxide.
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 Diluted hydrochloric acid
Mix one volume of concentrated hydrochloric acid solution, ρ (HCl) = 1,18 g/ml, with one volume of water.
5.3 Sulfuric acid , c = 0,05 mol/l.
5.4 Sodium or potassium hydroxide solution , carbonate free, c = 0,1 mol/l.
5.5 Sulfuric acid solution , approximately 30 % H 2 SO 4 (mass concentration), ammonia free.
5.6 Powdered iron , reduced in hydrogen.
The prescribed quantity of iron shall be able to reduce at least 0,05 g of nitrate nitrogen.
5.7 Sodium hydroxide solution , 30 % mass concentration, of approximately ρ (NaOH) = 1,33 g/ml,ammonia free.
5.8 Indicator solutions
5.8.1 Mixed indicator
Solution A: Dissolve 1 g of methyl red in 37 ml of sodium hydroxide solution c = 0,1 mol/l and make up to 1 l with water.
Solution B: Dissolve 1 g of methylene blue in water and make up to 1 l.
Mix one volume of solution A with two volumes of solution B.
This indicator is violet in acid solution, grey in neutral solution and green in alkaline solution. Use 0,5 ml (10 drops) of this indicator solution.
5.8.2 Methyl red indicator solution
Dissolve 0,1 g of methyl red in 50 ml of 95 % ethanol. Make up to 100 ml with water and filter if necessary.
This indicator may be used (4 to 5 drops) instead of that specified in 5.8.1.
5.9 Anti-bump granules, for example pumice stone, washed in hydrochloric acid and calcined.
EN 15558:2009 – Fertilizers – Determination of nitric and ammoniacal nitrogen according to Ulsch