Overview - ISO 28198:2018 (Toluene Insoluble Matter in Lecithin)
ISO 28198:2018 specifies a laboratory method to determine toluene insoluble matter (TIM) in vegetable lecithin formulations. TIM indicates impurities such as protein, carbohydrate-containing extraction residues and other solid contaminants. The method applies to all types of vegetable lecithin (Codex INS No. 322) and is used to support purity requirements and regulatory specifications. Notably, toluene is used as the solvent in this standard as a safer replacement for the carcinogenic benzene used in older methods.
Key topics and technical requirements
- Principle: Dissolve a representative lecithin test portion in toluene, filter the solution, dry the insoluble residue and weigh to calculate TIM as grams per 100 g.
- Sample preparation: Heat and homogenize the test sample (max 60 °C) before analysis; sampling methods are outside the method but ISO 5555 is recommended.
- Test portion and reagents: Typical test portion ≈ 10.00 g; use analytical-grade toluene (100 ml for dissolution; rinse twice with 25 ml).
- Filtration media: Glass filter crucible P40 (porosity 16–40 µm) is mandatory - other pore sizes produce different results and are not acceptable.
- Drying and weighing: Dry residue at (103 ± 2) °C, cool in a desiccator and weigh using an analytical balance (readability 0.001 g). Report TIM to two decimal places.
- Precision and validation: The standard includes results from interlaboratory studies and guidance on repeatability and reproducibility (see Annex A). It specifies procedural checks for constant mass and handling of turbid samples.
- Safety & cleaning: Follow hazardous-substance regulations for toluene handling; recommended cleaning procedures and limits on re-use of filter crucibles are provided.
Applications and who uses it
- Food additive manufacturers and lecithin suppliers - to verify product purity and meet specification limits.
- Quality control and analytical laboratories - routine testing of lecithin batches for TIM content.
- Regulatory agencies and standards bodies - to enforce purity requirements referenced in food additive regulations and Codex-related specifications.
- Research groups and certification bodies - for method validation, interlaboratory comparison and product compliance testing.
Related standards and references
- ISO 5555 - recommended sampling methods for oils and fats (sampling not included in ISO 28198).
- ISO 4793 - relates to filter porosity denominations (G3/P40).
- ISO 5725-1/2 - methods for evaluating precision (used for interlaboratory study evaluation).
- Codex Alimentarius (INS No. 322) - context for lecithin as a food additive.
Keywords: ISO 28198, toluene insoluble matter, TIM, lecithin testing, vegetable fats and oils, P40 filter crucible, analytical method, food additive purity.
