⛽ Sulfur in petroleum products — energy-dispersive X-ray fluorescence (EDXRF)
In short
The sample in a cell with a film in the X-ray beam; the intensity of the characteristic radiation of sulfur is compared with a calibration curve made from standards (0. The test is performed according to PN-EN ISO 8754:2026-02; Range (ISO 8754:2003): 0.03–5.00 % (m/m) sulfur. The procedure comprises 8 steps; it is used for: Control of the sulfur content in gasolines, middle distillates, fuel oils and residual oils, Base oils and lubricant blending components — quality control, Supervision of the sulfur content of marine and aviation fuel.
At a glance
- Standard: PN-EN ISO 8754:2026-02
- Category: Petrochemistry
- Procedure steps: 8
- Range (ISO 8754:2003): 0.03–5.00 % (m/m) sulfur
- Calibration standards: 4 ranges: 0.03–0.10; > 0.10–0.5; > 0.5–2.0; > 2.0–5.0 % (m/m); ≥ 3 primary standards
- Cell: Depth of the sample ≥ 3 mm (filling 3–20 mm), a 6 µm film of polyester, polypropylene or polycarbonate
Overview
The standard specifies a method of determining the sulfur content in petroleum products such as naphthas, unleaded motor gasolines, middle distillates, residual fuel oils, base oils and components; the description is based on the preview of ISO 8754:2003 (range 0.03–5.00 % by mass). The Polish Committee for Standardization has published PN-EN ISO 8754:2026-02 adopting ISO 8754:2025 (the third edition, August 2025), whose full content has not been checked — the table of contents of the new edition keeps the same arrangement: principle, reagents, apparatus, sampling, preparation of the instrument, calibration (primary standards, calibration standards, short- and long-term control), procedure, calculations, precision, with Annex A on matrix effects.
The determination may be interfered with by heavy metal additives (lead alkyls) and by silicon, phosphorus, calcium, oxygen, potassium, zinc, molybdenum, barium and the halogens when present in amounts above a few hundred mg/kg; some instruments compensate for matrix and spectral interferences by the deconvolution of the spectra and inter-element correction. With samples differing in their proportion of aromatic and paraffinic hydrocarbons the C/H ratio may interfere when it differs by one or more from that of the calibration materials. Instruments with a chamber for cells with Mylar film measure the sulfur in crude oil and its products from the ppm level to a few per cent (manufacturers declare for example ranges of 5 ppm–1 % and 1–5 %, a sample of 7 ml and a measuring time of 30–900 s).
The EDXRF method is one of the techniques for determining sulfur in fuels, beside WDXRF and UV fluorescence; it serves for the quality control of fuels and oils and for the supervision of the sulfur content of marine fuels.
Method principle
A test portion of the sample is placed in a beam emitted from an X-ray source; the excitation energy may come from a radioactive source (for example 55Fe) or from an X-ray tube. The excited characteristic X-radiation of sulfur is measured (a detector of high sensitivity at 2.3 keV, filters or other means of distinguishing the Kα line of sulfur from others), and the number of counts recorded is compared with a calibration curve (counts against sulfur content in % by mass) prepared on a series of calibration samples covering the range under test. The primary standards are prepared from dibenzothiophene (17.399 % S), dibutyl sulfide (21.915 % S) or thionaphthene (23.89 % S) in a white oil with a sulfur content of ≤ 20 mg/kg, or certified reference materials are used; at very low concentrations (below about 0.1 %) the diluent for the standards should be similar to the product under test, with a sulfur content preferably below 2 mg/kg.
Applications
- Control of the sulfur content in gasolines, middle distillates, fuel oils and residual oils
- Base oils and lubricant blending components — quality control
- Supervision of the sulfur content of marine and aviation fuel
- Rapid determinations in refinery laboratories and terminals (measurement without preparation of the sample)
Key parameters
| Parameter | Value |
|---|---|
| Range (ISO 8754:2003) | 0.03–5.00 % (m/m) sulfur |
| Calibration standards | 4 ranges: 0.03–0.10; > 0.10–0.5; > 0.5–2.0; > 2.0–5.0 % (m/m); ≥ 3 primary standards |
| Cell | Depth of the sample ≥ 3 mm (filling 3–20 mm), a 6 µm film of polyester, polypropylene or polycarbonate |
| Detection | A source with a significant X-ray flux above 2.5 keV; a detector sensitive at 2.3 keV |
| Control of the calibration | At least 2 points of each curve every week (setting-up standards); a full check at intervals of ≤ 3 months |
| Measurement | Two counts in the time recommended by the manufacturer; the mean of the counts |
Standard
- Standard number
- PN-EN ISO 8754:2026-02
- Title (PL)
- Przetwory naftowe — Oznaczanie zawartości siarki — Metoda dyspersyjnej rentgenowskiej spektrometrii fluorescencyjnej
- Title (EN)
- Petroleum products — Determination of sulfur content — Energy-dispersive X-ray fluorescence spectrometry
Step-by-step procedure
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Sampling and homogenisation of the sample
Take the samples according to ISO 3170 or ISO 3171; take the test portions after thorough mixing and division; warm viscous samples until they are liquid and homogenise them with the stirrer.
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Preparation of the instrument
Keep the analyser switched on continuously as far as possible, for stability. Clean and dry the cells thoroughly (disposable ones are not to be used again) and touch the film as little as possible.
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Primary standards
Prepare at least three primary standards: weigh the white oil and the sulfur compound to 0.1 mg according to table 1 (for example 5 % S: 40.0 g of oil + 16.1 g of DBT) and mix at room temperature (a magnetic stirrer; volatile compounds in a closed vessel). Calculate wS = m1·wS,c/(m1 + m2) to three decimal places.
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Calibration standards
Dilute the primary standards with white oil to the ranges of table 2 (without curvature fitting: 4 ranges; with fitting or with manual plotting: two adjacent ranges together), or use CRMs.
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Calibration
Cover the bottom of the cell with the film without touching it, fill it with the standard to 3–20 mm, with no bubbles between the film and the liquid, the film smooth and taut. Read each standard for the recommended counting time (usually a single reading; where the results are irregular, up to 4 replicates on fresh cells and portions — do not repeat the counts on the same cell). Prepare the calibration curve by linear regression (the sulfur as the independent variable).
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Control of the calibration
At least once a week check two points of each curve with setting-up standards; if the difference exceeds the repeatability — repeat the calibration. Carry out a full check at least every three months.
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Measurement of the sample
Fill the cell with a test portion of the sample as for the calibration and make two counts in the recommended time; calculate the mean. With volatile samples watch for bulging of the film after the cell is closed (venting); where there are losses by evaporation, make the second count on a fresh portion in a new cell and with a shorter time.
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Result
Read the sulfur content from the calibration curve (instruments may carry out this calculation automatically) and give it in % (m/m) or mg/kg together with a reference to the standard.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| EDXRF analyser | Any model with: an X-ray source (a tube or an isotope), an interchangeable cell with a film transparent to X-rays, a detector sensitive at 2.3 keV, filters, counting electronics with pulse height analysis, a display in counts or in % of sulfur; for example benchtop HDXRF instruments | — |
| Analytical balance | Accuracy 0.1 mg for the preparation of the standards | — |
| Stirrer | High-speed, shearing, non-aerating, for the homogenisation of viscous samples | — |
| Vessels for the standards | Narrow-necked 100 ml conical flasks with stoppers or bottles with a PE/PTFE seal; storage in dark bottles in a cool place (stable for more than 3 months) | — |
| Disposable cells and window film | Film 6 µm; disposable cells are not to be used again | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| White oil (light paraffin oil) | — | Of high purity, sulfur ≤ 20 mg/kg; for low concentrations a diluent similar to the product, sulfur < 2 mg/kg |
| Dibenzothiophene (DBT) | 132-65-0 | Nominal sulfur content 17.399 % (m/m) |
| Dibutyl sulfide (DBS) | 544-40-1 | Nominal sulfur content 21.915 % (m/m) |
| Thionaphthene (benzothiophene, TNA) | 95-15-8 | Nominal sulfur content 23.89 % (m/m); at a purity below 99 % certified materials or known impurities are required |
| Certified reference materials | — | From a national standardisation institution or an accredited supplier; in disputes the parties agree on a common set of standards |
Health and safety (OHS)
- An instrument with a radioactive source or an X-ray tube — work in accordance with the regulations on ionising radiation, check the tightness of the source, let only trained personnel handle the source
- Gasolines and naphthas are volatile and flammable — fill the cells in a fume hood, away from sources of ignition
- Aromatic samples may dissolve polycarbonate film — choose the film accordingly and protect the detector against leakage (a chamber with a drip tray)
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 8754:2026-02 — “Petroleum products — Determination of sulfur content — Energy-dispersive X-ray fluorescence spectrometry”.
How does this method work?
A test portion of the sample is placed in a beam emitted from an X-ray source; the excitation energy may come from a radioactive source (for example 55Fe) or from an X-ray tube. The excited characteristic X-radiation of sulfur is measured (a detector of high sensitivity at 2.
What is the measuring range and accuracy?
Range (ISO 8754:2003): 0.03–5.00 % (m/m) sulfur; Calibration standards: 4 ranges: 0.03–0.10; > 0.10–0.5; > 0.5–2.0; > 2.0–5.0 % (m/m); ≥ 3 primary standards; Cell: Depth of the sample ≥ 3 mm (filling 3–20 mm), a 6 µm film of polyester, polypropylene or polycarbonate; Detection: A source with a significant X-ray flux above 2.5 keV; a detector sensitive at 2.3 keV.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
EDXRF analyser, Analytical balance, Stirrer, Vessels for the standards, Disposable cells and window film.
Where is this test used?
Control of the sulfur content in gasolines, middle distillates, fuel oils and residual oils; Base oils and lubricant blending components — quality control; Supervision of the sulfur content of marine and aviation fuel; Rapid determinations in refinery laboratories and terminals (measurement without preparation of the sample).
What safety precautions apply?
An instrument with a radioactive source or an X-ray tube — work in accordance with the regulations on ionising radiation, check the tightness of the source, let only trained personnel handle the source; Gasolines and naphthas are volatile and flammable — fill the cells in a fume hood, away from sources of ignition; Aromatic samples may dissolve polycarbonate film — choose the film accordingly and protect the detector against leakage (a chamber with a drip tray).
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 8754.