🌱 Sulfur present as sulfates in fertilizer extracts — method A gravimetric (barium sulfate), method B ICP-OES, method C ion chromatography, PN-EN 15749

Physicochemistry PN-EN 15749

Overview

WHAT THE STANDARD COVERS. The scope from the PKN card of the 2023-01 edition, quoted in full: "This document specifies three different methods (methods A, B and C) for the determination of sulfur present in fertilizer extracts in the form of sulfates. Method A specifies the gravimetric method. Method B specifies the method using inductively coupled plasma optical emission spectrometry (ICP-OES). Method C specifies the method using ion chromatography (IC)" (our translation of the Polish card); the card of the 2012 edition has the same wording. We have the text of the methods from the EN 15749:2009 edition (a preview published as ISO/DIS 25749 — pages headed "EN 15749:2009 (E)", from the foreword to clause 7.6.2, i.e. the whole of method A and method B without its final formula; method C is not in the preview). Introduction: in interlaboratory tests on the same samples the three methods gave equivalent results, so the choice depends on the user and the equipment available. Sulfur is extracted under extraction standards (in the 2009 edition still the specifications CEN/TS 15925, 15926, 15960, 15961): total sulfur present in various forms, water-soluble sulfur present in various forms, total calcium, magnesium, sodium and sulfur in the form of sulfates, or their water-soluble fractions. Sampling is not part of the standard (EN 1482-1 is recommended), sample preparation — according to EN 1482-2. How the 2022 edition differs from 2009 — WE DO NOT KNOW: we did not have its text and the card does not say.

METHOD A — GRAVIMETRIC (EN 15749:2009, Clause 6). Reagents: hydrochloric acid diluted 1 + 1 (from acid of density 1.18 g/ml), barium chloride BaCl₂·2H₂O solution 122 g/l, silver nitrate solution 5 g/l, water of grade 3 according to EN ISO 3696. Apparatus: porcelain crucibles, water bath, drying oven 105 °C ± 1 °C, electric furnace 800 °C ± 50 °C. Procedure: an aliquot of the extract containing 20–100 mg of sulfur (50–250 mg of SO₃) is taken, 20 ml of diluted hydrochloric acid are added and the volume made up with water to about 300 ml; the solution is brought to the boil, about 20 ml of barium chloride solution are added dropwise with vigorous stirring and it is boiled for a few minutes; the beaker, covered with a watch glass, is kept for one hour in a boiling water bath, then hot (about 60 °C) until the liquid is clear. The precipitate is filtered through a slow ash-free filter and washed with hot water until the filtrate is free of chloride (silver nitrate test); the filter with the precipitate is dried in a weighed crucible, ashed at about 800 °C for half an hour, cooled in a desiccator and weighed to 0.1 mg. Calculation: 1 mg of barium sulfate corresponds to 0.137 mg of sulfur or 0.343 mg of SO₃; sulfur content as mass fraction in percent w_S = m₁ × 0.0137 × v₁ / (v₂ × m₂), where m₁ — mass of the precipitate in mg, m₂ — mass of the test portion in g, v₁ — volume of the extraction solution in ml, v₂ — volume of the aliquot in ml; a separate formula gives SO₃.

METHOD B — ICP-OES (EN 15749:2009, Clause 7, up to 7.6.2). Water of grade 2; sulfur stock solution 1000 mg/l from sodium sulfate dried for one hour at 105 °C (about 4.4375 g in 1000 ml; stable for several months at 4–6 °C; a commercial one is acceptable), stock solutions replaced after a year at the latest, the standard solution at least monthly. Spectrometer with radial viewing of the plasma (axial acceptable if the results are statistically equal), with background correction; for lines below 190 nm evacuated optics or optics purged with inert gas. Calibration by standard addition (about 20, 50 and 100 % of the expected content; an external calibration curve with matrix matching is acceptable if the results are statistically equal); test solution diluted to 10–150 mg/l of sulfur; blank; at least two replicates. Conditions from Table 1: line 181.978 nm (alternatives 180.676 and 182.568 nm), working range 1–150 mg/l, possible internal standard — molybdenum (202.030 nm, 281.615 nm). Result from linear regression over the additions, sulfur content in mg/kg of fertilizer.

STATUS (state of the cards on 29 September 2026). The card of PN-EN 15749:2023-01 (Polish version) has no "Wycofana" (withdrawn) header — the edition is CURRENT: Polish version published 06-12-2024, 32 pages, price group P, Chemical Sector, PKN technical committee KT 156 (Fertilizers), ICS 65.080, "Introduces: EN 15749:2022 [IDT]", "Supersedes: PN-EN 15749:2012 - Polish version". Card of PN-EN 15749:2012 (Polish version): "withdrawn and replaced by PN-EN 15749:2023-01 - English version", published 31-12-2012, "Withdrawal date: 23-01-2023", 23 pages, "Introduces: EN 15749:2009 [IDT]", "Supersedes: PN-EN 15749:2009 - English version", "Replaced by: PN-EN 15749:2023-01 - English version, PN-EN 15749:2023-01 - Polish version".

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17 September 2026, read on 28 September 2026). All records of number 15749: 19 entries at 13 laboratories. The 2023-01 edition — 11 laboratories (AB 779 once as "2023-1", AB 789 as "2023"), the 2012 edition — AB 284 and AB 1186. Method: gravimetric for all; "method A" explicitly — 11 laboratories, without the letter — AB 006 and AB 820. The "Laboratories" tab searches for records BEGINNING with "PN-EN 15749" and will show 12 laboratories — checked with the tab query on the labcoda.pl production server on 29 September 2026: 12; AB 1186 remains outside it (it records "PN-EN 15960:2011 PN-EN 15749:2012 met. A" in one string). Current scopes on the PCA website (read on 29 September 2026, issues from 7 March 2025 to 5 August 2026): all entries stand in the valid issues, every pair of range limits from the copy appears in the current document and no entry is suspended.

TEST ITEM AND RANGES. Mineral (inorganic) fertilizers — 12 laboratories; AB 006 more widely: also organo-mineral and organic fertilizers, compost, growing media and plant biostimulants and soil improvers. Quantities determined: total sulfur (with extraction under PN-EN 15960:2011 — 12 laboratories, at AB 006 and AB 180 also PN-EN 15925:2011) and water-soluble sulfur (with PN-EN 15961:2017-02 — 9 laboratories, at AB 006 and AB 180 also PN-EN 15926:2011); AB 284 writes "present in the form of sulfates", AB 333 — "soluble in water and hydrochloric acid", AB 921 names no extraction standard. Ranges: as S from 0.10 % (AB 180, AB 312, AB 759) to 25.0 % (AB 180, AB 333, AB 759) and 99.9 % (AB 006), as SO₃ from 0.25 % to 62.5 % (AB 180, AB 333); AB 006 gives, next to (0.50 - 99.9) % S, the range (1.3 - 250) % SO₃.

ALONGSIDE THIS STANDARD. Sulfur in fertilizers and plant cultivation aids under other documents is determined by AB 339 (PB 211, ICP-OES — natural, organic and organo-mineral fertilizers, soil improvers), AB 700 (PN-EN ISO 11885:2009 with PN-EN 16173:2012 and PN-EN 16174:2012, ICP-OES — compost, plant cultivation aids, digestate, (50 − 50000) mg/kg) and AB 1748 (PB-80, issue 1 of 25.07.2025, ICP-OES — growing media, (26 – 6310) mg/kg). Methods B and C of this standard are not cited by any laboratory in the copy. The extraction of total calcium, magnesium, sodium and sulfur under PN-EN 15960 has a separate Knowledge Base entry.

WHAT WE DO NOT GIVE. Method C (ion chromatography) and the final formula of method B — the preview ends before them; we did not have the text of the 2022 edition, so we do not know whether it changed the reagents, conditions or formulae of method A. We also do not give the precision data from interlaboratory tests.

Method principle

Sulfur brought into the extract as sulfates (under a separate extraction standard) is determined by one of three equivalent methods. Method A: sulfates are precipitated hot in hydrochloric acid medium with barium chloride; after clarification the barium sulfate precipitate is filtered, washed free of chloride, ashed at about 800 °C and weighed; 1 mg BaSO₄ corresponds to 0.137 mg S. Method B: measurement of sulfur emission by ICP-OES (line 181.978 nm) with standard-addition calibration. Method C: ion chromatography with a suppressor and conductivity detector (EN 15749:2009; the 2022 edition — the same scope according to the card).

Applications

• Total and water-soluble sulfur in mineral fertilizers — method A in the scopes of 13 laboratories
• Organo-mineral and organic fertilizers, compost, growing media and plant cultivation aids — AB 006

Key parameters

Standard

Standard number

PN-EN 15749:2023-01 (wersja polska; EN 15749:2022 IDT)

Title (PL)

Nawozy — Oznaczanie zawartości siarczanów trzema różnymi metodami

Title (EN)

Fertilizers — Determination of sulfates content using three different methods

Step-by-step procedure

1. Extraction

   Total or water-soluble sulfur is brought into solution under an extraction standard (e.g. PN-EN 15960, PN-EN 15961); the sample is prepared according to EN 1482-2.

2. Precipitation (method A)

   Aliquot of extract with 20–100 mg S + 20 ml HCl 1 + 1, made up to about 300 ml, boiling, dropwise addition of about 20 ml BaCl₂ with stirring, a few minutes of boiling, 1 h in a boiling water bath, standing hot (about 60 °C) until clear.

3. Filtration and washing

   Slow ash-free filter; washing with hot water until free of chloride (AgNO₃ test).

4. Ashing and weighing

   Drying in a weighed porcelain crucible, ashing at about 800 °C for half an hour, cooling in a desiccator, weighing to 0.1 mg.

5. Calculation

   w_S = m₁ × 0.0137 × v₁ / (v₂ × m₂) [%]; 1 mg BaSO₄ = 0.137 mg S = 0.343 mg SO₃ (EN 15749:2009).

6. Methods B and C

   ICP-OES with standard additions (181.978 nm, 1–150 mg/l) or ion chromatography; details of method C NOT GIVEN — outside the preview.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Barium chloride is toxic and concentrated hydrochloric acid corrosive — gloves and goggles, fume hood when boiling with acid
• SUBSTANTIVE NOTE: the standard determines sulfur in the extract — the result depends on the extraction standard (total or water-soluble sulfur); when asking for the test, state both standards

Frequently asked questions