Solvent Residue in Absolutes: Which Hexane Limits Exist
Asking whether hexane was used to make an absolute is the wrong question: in practice it nearly always was, and that is what "absolute" implies. The useful questions are how much is left, how it was measured, and against which number it is judged. That last part is where it gets awkward, because the best-known hexane limit comes from pharmaceuticals, a different one governs food oils, and we found no equivalent figure written for cosmetic fragrance materials.
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Shop Now →What the process leaves behind
Our absolute is solvent-extracted: flowers are washed with hexane to give a waxy concrete, then the concrete is washed with ethanol, chilled to drop the waxes out, filtered and concentrated. The steps are in concrete to absolute and what an absolute is. How completely each solvent is removed is the open question. Hexane is the one people ask about.
Why hexane draws attention: ATSDR's n-hexane ToxFAQs say breathing high concentrations can cause tingling or numbness in the hands and feet, with paralysis of the limbs possible with continued exposure, and that workers recovered after removal from exposure. That is about high inhaled exposure in workplaces. It is not a statement about residue in a fragrance material, and it does not tell you what an absolute contains.
The numbers that exist, and what each was written for
| Source | Hexane figure | Written for |
|---|---|---|
| ICH Q3C(R8), 22 April 2021 | Class 2; permitted daily exposure 2.9 mg/day; 290 ppm (Option 1) | Residual solvents in drug substances, excipients and drug products |
| Directive 2009/32/EC, Annex I Part II (retained UK text) | 1 mg/kg in fat, oil or cocoa butter; 5 mg/kg in defatted cereal germs; 10 mg/kg in food containing defatted protein products and flours; 30 mg/kg in defatted soya products sold to the consumer | Extraction solvents in foodstuffs |
| Same directive, Part III | 1 mg/kg | Flavourings prepared from natural flavouring materials |
| Cosmetic fragrance materials | None found in the sources we read | Not applicable |
ICH Q3C sorts solvents into classes. Class 2 is "solvents to be limited," meaning non-genotoxic animal carcinogens or possible causes of other irreversible toxicity such as neurotoxicity, or solvents suspected of other significant but reversible toxicities. Hexane is in Class 2 with a permitted daily exposure of 2.9 mg/day. The 290 ppm is not a separate finding: the guideline calculates it by assuming a product mass of 10 g taken daily (2.9 mg divided by 10 g = 0.29 mg/g = 290 ppm). Ethanol is Class 3, defined as low toxic potential with PDEs of 50 mg/day or more. The scope matters: the guideline applies to drug products, excludes those in clinical research and existing marketed drug products, and notes that "higher levels of residual solvents may be acceptable in certain cases such as short term (30 days or less) or topical application," with justification case by case. So borrowing "290 ppm" for a perfume oil is borrowing a drug yardstick that was built for something swallowed or injected daily.
The EU food directive sets far lower numbers for oils: 1 mg/kg, which is 1 ppm. The 290-fold gap between 290 ppm and 1 ppm is not a disagreement about hexane; it reflects different dose assumptions and different regulators. We read the text as published on legislation.gov.uk, which is the retained UK version of the EU directive; check the current EU consolidated text, because limits can change.
For cosmetics, we did not find a hexane limit for fragrance raw materials in what we read. We also searched the IFRA Standards library (51st Amendment, the latest listed) for "hexane" and "solvent" and found no entry. A regulatory consultant can tell you whether a limit applies in your market and product type.
Worked example: what a number would mean in your bottle
Suppose, purely as a yardstick, an absolute carried hexane at the ICH Option 1 figure of 290 ppm (290 mg/kg). This is a hypothetical for the arithmetic; we hold no figure for our absolute.
- Blended at 2% in a carrier, the finished oil carries 290 x 0.02 = 5.8 ppm.
- If someone applied 10 g of that blend in a day (a large amount, chosen to match ICH's 10 g assumption), the hexane load would be 5.8 mg/kg x 0.010 kg = 0.058 mg, about 2% of the 2.9 mg/day PDE, a factor of 50 below it.
- At 0.5% the same inputs give 1.45 ppm and 0.0145 mg.
- If the absolute instead carried 1 ppm (the food-oil figure), a 2% blend is 0.02 ppm.
Two cautions. The ICH figure assumes ingestion-type daily dosing of a drug, and skin or air exposure follows different rules; the arithmetic shows scale, not safety. And evaporation during blending, candle burning or diffusing changes where the solvent goes. The takeaway is narrower: a low ppm in a neat absolute becomes much lower in a diluted product, so the figure that matters most is the one on the lot you are buying, and for a 400 lb order that is a question worth getting answered before money moves.
How hexane gets measured, and why method matters
The standard approach for oils is static headspace gas chromatography: warm a weighed sample in a sealed vial, sample the vapour above it, and compare against calibration standards. A 2021 paper (Samsuri, Ang and Ng, International Journal of Analytical Chemistry) tuned this with a flame ionisation detector for four edible oils, using 5 g of oil per vial and heptane as internal standard. Reported hexane was 3.074 mg/kg in sunflower oil with a wide calibration range and 2.688 with a narrow one, a drop of about 13%; corn, sesame and palm showed the same direction (0.414 versus 0.358, 0.711 versus 0.602, 0.144 versus 0.126). Only sunflower exceeded the 1 mg/kg EU limit. That is edible oil, not absolute, and the authors' point is methodological: the calibration range moved the answer. For you, the lesson is that "ppm hexane" with no method, detection limit or date is half an answer.
What to ask, and what we publish
The certificate of analysis we publish for our absolute gives density, refractive index, optical rotation, appearance and smell for one batch. It has no residual solvent figure, and we publish none. If you need one, ask in writing before ordering and get the answer in writing. Useful questions for any supplier:
- Which solvents were used (hexane, ethanol, anything else), and is residual solvent measured per lot?
- By what method, with what detection limit, in what units (ppm is mg/kg), on which batch number and date?
- Against what limit is the result judged, and by whom (the supplier, a customer specification, a regulator)?
- Will the figure be on a document you can keep, with the lot number you are receiving?
For what else a certificate should show, see reading a COA; for label wording, reading an absolute's label; for the exposure side, Is honeysuckle oil safe?
A solvent figure tells you how a lot was made, and for anything you plan to sell, a regulatory consultant should decide which limit applies to your product.
Honeysuckle Absolute
Honeysuckle Absolute from our own shop, in sizes from 0.5 oz to bulk.
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Shop Now →Sources & Further Reading
- ICH, 2021. Q3C(R8) Impurities: Guideline for Residual Solvents (Step 4, 22 April 2021). database.ich.org Q3C(R8)
- Directive 2009/32/EC, Annex I (retained UK text). legislation.gov.uk/eudr/2009/32
- ATSDR. ToxFAQs for n-Hexane. wwwn.cdc.gov/TSP/ToxFAQs
- Samsuri AH, Ang MY, Ng SY, 2021. Optimization of Residual Hexane in Edible Oils Analysis Using Static Headspace Gas Chromatography. Int J Anal Chem 2021:1941336. PMC8570895
- IFRA. Standards library (searched for hexane and solvent). ifrafragrance.org/standards-library