⛽ Sulfur Content in Fuels

Petrochemistry PN-EN ISO 20846

Overview

STATUS (as of 30.10.2026). PN-EN ISO 20846:2020-03 — Polish and English versions, implements EN ISO 20846:2019 and ISO 20846:2019 [IDT]; the Polish version was published on 08.07.2021 and replaced PN-EN ISO 20846:2012. In the PKN catalogue the standard has no withdrawal note. At the international level the fourth edition ISO 20846:2026 was published on 10.07.2026 (the 2019 edition was withdrawn) and was also adopted as EN ISO 20846:2026; a Polish adoption of this edition is not yet in the PKN catalogue. Changes according to the foreword of the 2026 edition: extension of the scope to blends with FAME contents from 50 % to 100 % (B100) and additional instructions on multipoint calibration and its validity.

SCOPE (clause 1, 2026 edition). Sulfur content from 3 mg/kg to 500 mg/kg in motor petrols containing up to 3.7 % (m/m) oxygen (including those blended with ethanol up to about 10 % (V/V)) and in diesel fuels, including those with up to about 50 % (V/V) FAME; from 3 mg/kg to 45 mg/kg in synthetic fuels such as HVO and GTL; from 3 mg/kg to 30 mg/kg in neat FAME (B100) and in diesel fuels with more than 50 % FAME. The 2019 edition covered diesel fuels with up to about 30 % (V/V) FAME and did not cover B100. Other products (for example process feeds and effluents) and other sulfur contents can be analysed by the method, but precision data have been established only for automotive fuels within the stated ranges. Halogens at concentrations above approximately 3 500 mg/kg interfere with the determination; the 2019 edition also points to a possible nitrogen interference (6.5).

PRINCIPLE AND APPARATUS (clauses 4 and 6). A hydrocarbon sample is injected directly or placed in a sample boat; in a combustion tube at 1 000 °C to 1 100 °C the sulfur is oxidized to SO₂ in an oxygen-rich atmosphere. The water produced in the combustion is removed and the combustion gases are exposed to ultraviolet radiation: SO₂ absorbs the energy of the radiation and is converted to an excited state, and the fluorescence emitted on its return to the ground state is detected by a photomultiplier tube — its signal is a measure of the sulfur content. Apparatus according to the 2019 edition: electric furnace, quartz combustion tube allowing direct injection into the pyrolysis zone, flow meters for oxygen and carrier gas, drier, UV fluorescence detector, microlitre syringe from 5 µl to 50 µl, injection system delivering the sample at a constant rate of approximately 1 µl/s maximum (boat injection systems — if they meet the precision requirements of clause 13), balance weighing to the nearest 0.1 mg and Class A volumetric flasks according to ISO 1042. The standard recommends checking that the instrument compensates for the nitrogen interference: for example, 2-ethylhexyl nitrate (EHN) added at 2 000 mg/kg to a diesel fuel containing 10 mg/kg sulfur increased the result by 0–1.7 mg/kg.

REAGENTS AND STANDARDS (clause 5). Inert gas — argon or helium with a purity above 99.998 % (V/V); oxygen with a purity above 99.75 % (V/V). Solvent: toluene or isooctane of analytical grade, or a solvent of similar composition to the sample; the sulfur contributed by the solvent is taken into account when preparing standards and diluting samples, unless it is non-detectable (according to a note of the 2026 edition, usually below 0.5 mg/kg). Sulfur compounds with a purity of at least 99 % (m/m) — for example dibenzothiophene (17.399 % S), di-n-butyl sulfide (21.915 % S), di-n-butyl disulfide (in the 2026 edition; 35.950 % S) and thionaphthene, i.e. benzothiophene (23.890 % S) — or certified reference materials produced in accordance with ISO 17034. A stock solution of about 1 000 mg/l sulfur is prepared by weighing 0.574 8 g DBT, 0.456 3 g DBS, 0.278 1 g DBDS or 0.418 6 g TNA into a 100 ml flask; stored in a refrigerator it remains valid for about three months. Calibration solutions are prepared by dilution; in a refrigerator those with more than 30 mg/kg sulfur remain valid for at least one month, poorer ones for a shorter time.

PREPARATION (clauses 7–8, 2019 edition). Samples are taken according to ISO 3170 or ISO 3171, kept at as low a temperature as practicable, not left uncovered longer than necessary and analysed as soon as possible to avoid loss of sulfur or contamination; samples collected below room temperature can expand and rupture the container, so it is not filled to the top. Before taking a test portion the sample is thoroughly mixed in its container. The instrument must be stabilized and leak-free, and the gas pressures and flow rates are set according to the manufacturer’s instructions.

WHAT WE DO NOT GIVE HERE. The way of multipoint and single-point calibration and its verification (clauses 9 and 11), the course of the determination (clause 10), the volume of sample injected or the precision values — repeatability and reproducibility (clause 13) — according to either edition: we only know the titles of these clauses.

Method principle

The sample is introduced directly or in a boat into a combustion tube at 1 000 °C to 1 100 °C, where the sulfur is oxidized to SO₂ in an oxygen-rich atmosphere. After removal of water the combustion gases are exposed to ultraviolet radiation; the excited SO₂ molecules emit fluorescence, which is detected by a photomultiplier tube.

The photomultiplier signal is a measure of the sulfur content; the result refers to a calibration with solutions of sulfur compounds of known content or with certified reference materials.

Applications

• Motor petrols with up to 3.7 % (m/m) oxygen, including blends with ethanol up to about 10 % (V/V) — from 3 to 500 mg/kg (clause 1)
• Diesel fuels with FAME — up to about 50 % (V/V) according to the 2026 edition, up to about 30 % (V/V) according to the 2019 edition — from 3 to 500 mg/kg (clause 1)
• Synthetic fuels HVO and GTL — from 3 to 45 mg/kg (clause 1)
• Neat FAME (B100) and diesel with more than 50 % FAME — from 3 to 30 mg/kg, only according to the ISO 20846:2026 edition (clause 1)
• Motor petrol and diesel fuel — requirement of the Polish regulation on quality requirements for liquid fuels: at most 10.0 mg/kg sulfur (Dz.U. 2024 item 1018, Annex 1 No 5 and Annex 3 No 5)
• Process feeds and effluents — determination possible, but without established precision data (clause 1)

Key parameters

Standard

Standard number

PN-EN ISO 20846:2020-03

Title (PL)

Przetwory naftowe — Oznaczanie zawartości siarki w paliwach do pojazdów samochodowych — Metoda fluorescencji w nadfiolecie

Title (EN)

Petroleum products — Determination of sulfur content of automotive fuels — Ultraviolet fluorescence method

Step-by-step procedure

1. Sampling and storage

   According to ISO 3170 or ISO 3171; as low a temperature as practicable, for cold samples the container not filled to the top, analysis as soon as possible; before taking a test portion the sample is mixed in its container (2019 edition, clause 7).

2. Preparing the instrument

   Checking stabilization and leak-tightness, setting gas pressures and flow rates according to the manufacturer’s instructions (2019 edition, clause 8).

3. Standards and calibration

   Calibration solutions from the stock solution or reference materials; multipoint or single-point calibration and its verification — clauses 9 and 11 (details outside the available text).

4. Determination

   Direct or boat injection, combustion at 1 000 °C to 1 100 °C and measurement of the SO₂ fluorescence — clause 10.

5. Result

   Calculation according to clause 11, with a correction for the sulfur from the solvent if the sample was diluted; result in mg/kg (clause 12).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Oxygen vigorously accelerates combustion (warning to 5.2); the solvents — toluene and isooctane — are flammable (warning to 5.3)
• UV radiation from the detector is injurious to health — protect the eyes from direct, scattered and residual light (2019 edition, warning to 6.5)
• Samples collected below room temperature can expand and rupture the container — leave free space (2019 edition, caution to 7.1)
• The furnace operates at 1 000 °C to 1 100 °C — risk of burns

Frequently asked questions