Overview
ISO 3735:1999 specifies a standardized extraction method for the determination of sediment in crude petroleum and fuel oils. The method uses hot toluene extraction of a measured test portion in a refractory extraction thimble, with results reported as percentage by mass (sediment by extraction). The procedure is designed for sediment levels typically in the range 0.01 % (m/m) to 0.40 % (m/m), although higher concentrations can be measured.
Key topics and requirements
- Principle: Extract the test portion in a porous thimble with hot toluene until the residue reaches constant mass.
- Reagents: Methylbenzene (toluene), ISO 5272 grade 2.
- Test portion: ≈10 g taken immediately after thorough mixing; do not pre-weigh to an exact mass.
- Apparatus:
- Extraction flask (1 L Erlenmeyer with ≥50 mm neck).
- Condensing coil (metal coil on lid) and thimble basket.
- Extraction thimble: refractory, pore size index P16 (ISO 4793), 25 mm × 70 mm, mass 15–17 g.
- Heater (hotplate preferred), oven (115–120 °C), desiccator for cooling, analytical balance (0.1 mg).
- Extraction details:
- Add 150–200 ml toluene; extract about 30 min after solvent from thimble runs colourless.
- Ensure toluene/oil level in thimble stays ≤ 20 mm from top.
- For samples >10 % (V/V) water, use a water cup to collect azeotroped water.
- Dry thimble 1 h at 115–120 °C, cool 1 h, weigh to 0.1 mg; repeat extractions until two successive masses differ ≤ 0.2 mg.
- Calculation: Sediment S (%) = (m3 − m1) / (m2 − m1) × 100, where m1 = empty thimble, m2 = thimble + test portion, m3 = thimble + sediment.
- Reporting: Round to nearest 0.01 % (m/m); state mixing procedure and sample temperatures before and after mixing.
- Precision: Reproducibility given as R = 0.033 + 0.255 S (S in % mass); see clause 11 for repeatability/reproducibility guidance.
- Caveats: Samples with significant inorganic salts can yield overestimated sediment because salts may be retained in the thimble. The method involves hazardous solvents-observe safety practices.
Applications and users
ISO 3735:1999 is used by:
- Petroleum testing laboratories and quality control (QC) teams
- Crude oil producers, refiners and fuel manufacturers
- Pipeline operators, marine bunkering inspectors and fuel traders
- Regulatory and compliance bodies monitoring fuel quality
Use cases include batch acceptance testing, custody transfer checks, and routine QC to quantify insoluble sediment that can affect refining, fuel handling and engine performance.
Related standards
- ISO 3170 / ISO 3171 - Sampling of petroleum liquids (manual and automatic)
- ISO 4793 - Sintered filters (thimble porosity classification)
- ISO 5272 - Toluene specifications
- ISO 1773 - Laboratory glassware (boiling flasks)
Keywords: ISO 3735:1999, sediment determination, toluene extraction, crude petroleum, fuel oils, extraction thimble, sediment by extraction, petroleum testing, fuel quality.