🌱 Determination of total nitrogen in fertilizers containing nitrogen only as nitric, ammoniacal and urea nitrogen — method A (according to ISO 5315:1984): reduction of nitrate to ammonia with chromium powder in acid medium, digestion with concentrated sulfuric acid and a catalyst, distillation of ammonia from an alkaline solution into an excess of standard sulfuric acid and back-titration with sodium hydroxide against methyl red; method B: as A, but reduction with iron powder and tin(II) chloride; both give equivalent results, PN-EN 15750

Physicochemistry PN-EN 15750

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of SIST EN 15750:2010 (English text of EN 15750:2009): from the title page through the contents, foreword, introduction and Clauses 1–5 to 6.2.2 (distillation apparatus) on page 7 inclusive. Outside the sample remain the rest of method A (apparatus from Figure 1, procedure, calculation), the whole of method B (Clause 7), precision of both methods (8), test report (9) and Annex A (statistical results of the inter-laboratory tests).

ACCORDING TO THE TEXT OF EN 15750:2009 (foreword, introduction, Clauses 1–6.2.2). The standard was prepared by CEN/TC 260 “Fertilizers and liming materials” (secretariat DIN) under a mandate from the European Commission and EFTA; CEN approved it on 20.09.2009; it superseded CEN/TS 15750:2008. Introduction: the document gives two different methods for determining the total nitrogen content in fertilizers; according to the statistical results of inter-laboratory tests on the same samples both give equivalent results and either can be used at the user’s decision. Scope (1): method A — titrimetric method after distillation according to ISO 5315:1984; method B — with reduction of nitrate by iron and tin(II) chloride. References (2): EN 1482-2 (sample preparation), EN 12944-1 and EN 12944-2 (vocabulary of fertilizers and liming materials), EN ISO 385 (burettes), EN ISO 3696 (water). Terms (3): according to EN 12944-1:1999 and EN 12944-2:1999. Principle (4): method A — reduction of nitrate to ammonia by chromium powder in acid medium, conversion of organic and urea nitrogen into ammonium sulfate by digestion with concentrated sulfuric acid in the presence of a catalyst, distillation of ammonia from an alkaline solution, absorption in an excess of standard volumetric sulfuric acid and back-titration with standard volumetric sodium hydroxide against methyl red or screened methyl red; method B — the same, but nitrate is reduced by iron powder and tin chloride in acid medium, and the titration uses an indicator solution. Sampling and sample preparation (5): sampling is not part of the methods (recommended according to EN 1482-1); the sample is prepared according to EN 1482-2. Reagents of method A (6.1): only reagents of recognized analytical grade, in particular with low nitrogen content, and grade 3 water according to EN ISO 3696; chromium metal powder of particle size up to 250 µm; fused aluminium oxide (pumice is suitable); anti-foaming agent, e.g. paraffin wax of melting point not lower than 100 °C or a silicone; ammonium nitrate dried at 100 °C to constant mass; finely ground digestion catalyst mixture — 1000 g potassium sulfate and 50 g copper(II) sulfate pentahydrate; concentrated sulfuric acid (about 1,84 g/ml); concentrated hydrochloric acid (about 1,18 g/ml); sodium hydroxide about 400 g/l; standard sodium hydroxide 0,10 mol/l; standard sulfuric acid 0,25, 0,10 and 0,05 mol/l; indicator — screened methyl red (50 ml of 2 g/l methyl red and 50 ml of 1 g/l methylene blue in ethanol) or methyl red (0,1 g in 50 ml of 95 % ethanol); wide-range pH indicator paper. Apparatus (6.2): digestion apparatus with an 800 ml Kjeldahl flask and a pear-shaped glass stopper; distillation apparatus connected with rubber bungs and tubing or spherical ground glass joints — spherical joints should be held with spring clamps to keep them leak-tight, and bungs and tubing are replaced when they begin to perish or wear; an automatic distillation apparatus may be used if the results are statistically equivalent.

STATUS (as of 03.10.2026). The PKN search (term “PN-EN 15750”, 03.10.2026) shows PN-EN 15750:2009 in the Polish and English versions (both “Introduces: EN 15750:2009 [IDT]”) without a withdrawal note; the remaining results are parts of the PN-EN ISO 15750 series, a different standard. In the iTeh catalogue (read on 03.10.2026) EN 15750:2009 has the status “Published”, stage 90.93 (decision to confirm after review) since 20.08.2026.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 15750 appears in 5 records at 5 laboratories: AB 180, AB 277, AB 312, AB 339, AB 1616. In the current PCA documents (read on 03.10.2026, issues from 14.10.2025 to 22.07.2026) the number appears in 5 rows — one at each; in each of the five documents the number of page markers equals the number of PDF pages, without repetitions; a search of all 1291 PCA documents downloaded from BIP on 03.10.2026 found no laboratories outside the database copy (17 laboratories on the list have no link to a scope document on BIP). The laboratories indicate the method: A — AB 180 (“PN-EN 15750:2009 metoda A”), AB 1616 (“PN-EN 15750:2009 met. A”) and AB 339 (“PB 200, PN-EN 15750 met.A”); B — AB 277 (“PN-EN 15750:2009 met B”) and AB 312 (“PN-EN 15750:2009 met. B”). None of these items is suspended; the AB 339 document contains a note on the suspension of part of the scope at the request of the body (items in bold italics), but the row with PN-EN 15750 is not marked that way. The “Laboratories” tab (term “PN-EN 15750”) shows 4 laboratories: AB 180, AB 277, AB 312 and AB 1616; AB 339 is under “PB 200”, because that designation comes first for it — checked with tab queries on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Object: inorganic (mineral) fertilizers (AB 180, AB 277, AB 312, AB 1616), natural, organic and organo-mineral fertilizers (AB 339, item in the flexible scope of accreditation). Characteristic: total nitrogen content (AB 180, AB 277, AB 1616), total ammoniacal, nitric and urea nitrogen content (AB 312), nitrogen content (AB 339), titrimetric method. Ranges: (1,00–47,0) % (AB 180), (1,0–27,0) % (AB 277, AB 312), (4,50–46,50) % (AB 1616).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With the choice of standard: the method concerns fertilizers with nitrogen only in nitric, ammoniacal and urea form (title, 1). With reagents: reagents with low nitrogen content and grade 3 water (6.1). With distillation: leak-tightness of joints and worn bungs and tubing (6.2.2); an automatic apparatus only with statistically equivalent results. With comparisons: methods A and B were found equivalent, but the laboratory states which one it uses.

WHAT WE DO NOT GIVE. We did not read the course of the determination (test portions, volumes, digestion and distillation times), the blank test, the control test with ammonium nitrate, the calculation formulae, method B in detail or the precision data (from 6.2.3, Clauses 7–9, Annex A).

Method principle

Nitrate in the fertilizer sample is reduced to ammonia in acid medium — with chromium powder (method A) or with iron powder and tin(II) chloride (method B). Organic and urea nitrogen is converted into ammonium sulfate by digestion with concentrated sulfuric acid and a catalyst. Ammonia is distilled from an alkaline solution into an excess of standard sulfuric acid, and the excess is back-titrated with standard sodium hydroxide against an indicator.

Applications

• Fertilizers containing nitrogen only in nitric, ammoniacal and urea form (1)
• Determination of total nitrogen content — two equivalent methods to choose from (introduction)
• Mineral, natural, organic and organo-mineral fertilizers — items in the accreditation scopes of 5 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN 15750:2009

Title (PL)

Nawozy — Oznaczanie azotu całkowitego w nawozach zawierających azot wyłącznie w formie azotanowej, amonowej i mocznikowej dwiema różnymi metodami

Title (EN)

Fertilizers — Determination of total nitrogen in fertilizers containing nitrogen only as nitric, ammoniacal and urea nitrogen by two different methods

Step-by-step procedure

1. Sample

   Preparation according to EN 1482-2 (5). PN-EN 15750:2009 without a withdrawal note (03.10.2026).

2. Reduction of nitrate

   Chromium powder (A) or iron powder and tin(II) chloride (B) in acid medium (4).

3. Digestion

   Concentrated sulfuric acid with catalyst in a Kjeldahl flask (4, 6.2.1).

4. Distillation and titration

   Ammonia from an alkaline solution into standard sulfuric acid, back-titration of the excess with sodium hydroxide (4).

5. Result

   Calculation, precision and report according to Clauses 6–9 (not read in this part).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Concentrated sulfuric and hydrochloric acids, hot digestion — fume hood, eye and hand protection
• Sodium hydroxide 400 g/l — corrosive substance
• Chromium powder and tin compounds — handling and waste disposal according to safety data sheets

Frequently asked questions