🌱 Total nitrogen in urea and nitrate-free urea fertilizers — conversion of urea into ammonia by boiling with sulfuric acid (Kjeldahl tablets with selenium), distillation of ammonia from an alkaline solution into an excess of standard sulfuric acid, back-titration of the excess with alkali, PN-EN 15478

Physicochemistry PN-EN 15478

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN 15478:2009 (Polish version), in full (our translation of the Polish card text): “This European Standard specifies a method for the determination of total nitrogen in urea. This method applies exclusively to urea fertilizers which do not contain nitrates.” We read the text of the standard in the preview of SIST EN 15478:2009 (EN 15478:2009) from the cover to Figure 2 (distillation apparatus 2, page 7); we do not have the rest — Figures 3 and 4, sampling and sample preparation (7), procedure (8), calculation (9), precision (10), test report (11) and Annex A with the results of the inter-laboratory tests.

ACCORDING TO THE TEXT OF EN 15478:2009 (foreword, clauses 1–6.1, Figures 1–2). The standard was prepared by CEN/TC 260 “Fertilizers and liming materials” (secretariat DIN) under a mandate of the European Commission and EFTA; it superseded the technical specification CEN/TS 15478:2006. Scope (Clause 1): total nitrogen in urea; the method is applied exclusively to urea fertilizers which are nitrate free. Normative references: EN 1482-2 (preparation of fertilizer samples), EN 12944-1:1999 and EN 12944-2:1999 (fertilizer vocabulary), EN ISO 3696:1995 (water for analytical use). Principle (Clause 4): urea is transformed quantitatively into ammonia by boiling in the presence of sulfuric acid; the ammonia is distilled from an alkaline medium and the distillate collected in an excess of standard sulfuric acid; the excess acid is titrated with a standard alkaline solution. Reagents (Clause 5): only of recognized analytical grade; distilled or demineralized water, free from carbon dioxide and all nitrogenous compounds (grade 3 according to EN ISO 3696:1995); Kjeldahl tablets of 5 g containing 100 parts K2SO4 to 1 part selenium (5.2); concentrated sulfuric acid, ρ20 = 1,84 g/ml (5.3); sodium hydroxide solution about 500 g/l (5.4); sulfuric acid c = 0,05 mol/l and carbonate-free sodium or potassium hydroxide solution c = 0,1 mol/l — for the blank test (5.5, 5.6); sulfuric acid c = 0,5 mol/l (5.7) and carbonate-free sodium or potassium hydroxide solution c = 1,0 mol/l (5.8); mixed indicator (5.9.1): solution A — 1 g of methyl red in 37 ml of 0,1 mol/l sodium hydroxide solution, made up to 1 l with water, solution B — 1 g of methylene blue in 1 l of water, one volume of A mixed with two volumes of B; the indicator is violet in acid solution, grey in neutral and green in alkaline solution, 0,5 ml (10 drops) is used; instead, 4–5 drops of methyl red may be used (5.9.2), red in acid and yellow in alkaline solution; anti-bump granules, e.g. pumice stone washed in hydrochloric acid and calcined (5.10); urea p.a. (5.11). Apparatus (6.1): distillation apparatus consisting of a round-bottomed flask of suitable capacity connected to a condenser by a splash head, made of borosilicate glass; recommended types are shown in Figures 1–4; automatic distillation apparatus may be used if the results are statistically equivalent. Figure 1: round-bottomed long-necked flask of 1000 ml, distillation tube with splash head connected to the condenser by a spherical joint No 18 (or a rubber connection), funnel with a PTFE tap for adding sodium hydroxide, six-bulb condenser, 500 ml flask for the distillate. Figure 2: round-bottomed short-necked flask of 1000 ml with a spherical joint No 35, distillation tube with splash head and a side funnel with a PTFE tap, six-bulb condenser, 500 ml flask for the distillate; here the read preview ends.

STATUS (cards as of 02.10.2026). The card of PN-EN 15478:2009 (Polish version) has no “Withdrawn” header — the standard is CURRENT: published 25-09-2014, 18 pages, price group J, Chemistry Sector, KT 156 Fertilizers, ICS 65.080, “Introduces: EN 15478:2009 [IDT]”. Card of PN-EN 15478:2009 (English version): no “Withdrawn” header, published 16-02-2009, 14 pages, price group G, “Scope” field: “A method for determining total nitrogen in urea is described. The method applies to urea fertilizers which do not contain nitrates”. The PKN search for “PN-EN 15478” (02.10.2026) shows only these two versions of the 2009 edition; neither card has a “Replaces” or “Replaced by” entry.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 15478 appears in 9 records of 9 laboratories: AB 006, AB 180, AB 277, AB 284, AB 312, AB 759, AB 779, AB 789, AB 827. Current scopes on the PCA website (read 02.10.2026, scope issues from 07.03.2025 to 05.08.2026): one item at each, everywhere “PN-EN 15478:2009”; at AB 180 the same item also lists PN-EN 15604:2012 and PN-EN 15750:2009 method A. None of these items is suspended. The “Laboratories” tab searches for entries BEGINNING WITH “PN-EN 15478” and shows all 9 laboratories — checked with the tab query on the production server labcoda.pl on 02.10.2026: 9 laboratories and 9 items; under “EN 15478” — 0.

WHAT THE LABORATORIES TEST (items in PCA). Object: urea — AB 006, AB 284, AB 759, AB 789, AB 827; mineral (inorganic) fertilizers — AB 180, AB 277, AB 312, AB 779 (at AB 312 and AB 779 the quantity is called “content of total amide nitrogen in urea”). Quantity: “total nitrogen content” — AB 180, AB 277, AB 284, AB 759, AB 789, AB 827; “amide nitrogen content” — AB 006; “content of total amide nitrogen in urea” — AB 312, AB 779. Everywhere “Titrimetric method”. Ranges: (22,0–46,5) % (AB 006), (1,00–47,0) % (AB 180, jointly for three standards), (0,50–50,0) % (AB 277), (5,0–48,6) % (AB 284), (1,00–50,0) % (AB 312), (40,0–50,0) % (AB 759), (14,0–47,0) % (AB 779), (31,0–46,6) % (AB 789), (30,0–50,0) % (AB 827).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With the sample: the method applies EXCLUSIVELY to nitrate-free urea fertilizers — the scope of the standard excludes fertilizers containing nitrates; the items described generally as “mineral (inorganic) fertilizers” (AB 180, AB 277) cover more objects than the scope of this standard allows (at AB 180 the same item also lists PN-EN 15604:2012 and PN-EN 15750:2009 method A — we do not describe their scopes here). With the name: the scopes give “total nitrogen”, “amide nitrogen” or “total amide nitrogen” — the standard determines total nitrogen in urea; the names in the scopes are not names from the standard. With the reagents: the water must be free from CO2 and nitrogen compounds (grade 3), and the alkali solutions for titration — carbonate free; the blank test has separate 0,05 mol/l and 0,1 mol/l solutions. With the apparatus: automatic apparatus may be used only with results statistically equivalent to the apparatus of Figures 1–4.

WHAT WE DO NOT GIVE. We do not have Figures 3 and 4, Clause 7 (sampling and sample preparation according to EN 1482-2), Clause 8 (test portion mass, quantity of acid and tablets, boiling time, volumes in distillation and titration, conduct of the blank test), Clause 9 (formula for the nitrogen content), Clause 10 (repeatability and reproducibility) or Annex A — so we do not give the test portion, times, formula or precision.

Method principle

Urea is transformed quantitatively into ammonia by boiling with sulfuric acid (with Kjeldahl tablets containing potassium sulfate and selenium); after making the solution alkaline with sodium hydroxide, the ammonia is distilled into an excess of standard sulfuric acid, and the excess acid is titrated with a standard carbonate-free sodium or potassium hydroxide solution using a mixed indicator (methyl red with methylene blue) or methyl red; total nitrogen is calculated from the difference.

Applications

• Urea — total or amide nitrogen in the scopes of 5 laboratories (AB 006, AB 284, AB 759, AB 789, AB 827)
• Mineral (inorganic) fertilizers — “total amide nitrogen in urea” (AB 312, AB 779) or total nitrogen (AB 180, AB 277) — within the scope of the standard: nitrate-free urea fertilizers
• Nitrogen content of urea — ranges in the laboratories' certificates from 0,50 % to 50,0 % N

Key parameters

Standard

Standard number

PN-EN 15478:2009 (wersja polska i angielska; EN 15478:2009 IDT)

Title (PL)

Nawozy — Oznaczanie azotu całkowitego w moczniku

Title (EN)

Fertilizers — Determination of total nitrogen in urea

Step-by-step procedure

1. Sample

   Sampling and sample preparation according to Clause 7 and EN 1482-2 — details NOT GIVEN; only nitrate-free urea fertilizers. PN-EN 15478:2009 current (cards as of 02.10.2026).

2. Conversion of urea into ammonia

   Boiling the test portion with concentrated sulfuric acid and Kjeldahl tablets (K2SO4 + Se) — test portion mass, quantities and time NOT GIVEN.

3. Distillation

   Making the solution alkaline with sodium hydroxide about 500 g/l through the funnel with PTFE tap and distilling the ammonia into an excess of standard sulfuric acid in the 500 ml flask; anti-bump granules; volumes — NOT GIVEN.

4. Titration

   Titrating the excess acid with standard carbonate-free NaOH or KOH solution using the mixed indicator (change from violet through grey to green) or methyl red (from red to yellow).

5. Blank test and result

   Blank test with 0,05 mol/l acid and 0,1 mol/l alkali; calculation of the total nitrogen content (Clause 9) and precision (Clause 10) — formula and values NOT GIVEN.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Kjeldahl tablets contain selenium (toxic); concentrated sulfuric acid and NaOH 500 g/l solution are corrosive; boiling with acid — fumes, work in a fume hood; the read part of the standard contains no safety warnings
• TECHNICAL NOTE: the method applies only to nitrate-free urea fertilizers — a result for a fertilizer containing nitrates is not a result according to this standard; the names “amide nitrogen” in the scopes do not change the fact that the standard determines total nitrogen in urea

Frequently asked questions