Buyer guides
Methanol grades explained
Five grade families, what separates them, and why the difference is almost never the headline purity figure.
- IMPCA purity
- ≥99.85% w/w
- IMPCA water
- ≤0.100% w/w
- Grade AA origin
- O-M-232
- CAS
- 67-56-1
Grade is the word suppliers use for two different things, and the ambiguity causes more purchasing errors than any other single term in the trade. Sometimes it means a formal specification with published limits and named test methods. Sometimes it means an internal product code that reflects nothing more than which tank the material came out of. A buyer who does not know which one they are being quoted has not really compared anything.
Commercially there are five families worth knowing. Bulk trade grades, which means the IMPCA reference specification and Grade AA. Technical or industrial grade, which is a looser commercial category. Analytical grades for chromatography and spectroscopy. And pharmacopoeial material, certified against a monograph rather than a trade specification. They differ far less in headline purity than most buyers expect, and far more in what else is controlled.
Key points
- The gap between industrial and analytical methanol is not purity. All of them are around 99.85% or better. The difference is which trace impurities are controlled and how tightly.
- IMPCA and Grade AA are close cousins and are frequently quoted together on the same producer certificate.
- “Technical grade” is a commercial label, not a standard. Ask what specification sits behind it or you are buying an adjective.
- HPLC and gradient grades are controlled on ultraviolet absorbance and evaporation residue, properties a bulk trade specification says nothing about.
- Cost separation between the families is very large. Analytical grades sit in a different order of magnitude from bulk, driven by packaging, testing and small-lot handling rather than by the molecule.
- Specify by named standard, not by application. “Solvent grade” means whatever the supplier's price list says it means.
Bulk trade grades
IMPCA reference specification methanol is the global standard for bulk trade. It sets purity at a minimum of 99.85% by weight on a dry basis and water at a maximum of 0.100% by weight, along with limits on acetone, ethanol, chloride, iron, sulphur, acidity, colour, distillation range and several other parameters. The IMPCA reference specification covers the full table and what it does not cover.
Grade AA originates in US Federal Specification O-M-232. It is worth being precise about the paperwork here, because it is routinely garbled: O-M-232 is the specification document and ASTM D1152 is the associated test standard. They are two separate publications and a supplier quoting “ASTM Grade AA” is conflating them. In practice producers publish sales specifications that satisfy both IMPCA and Grade AA on the same certificate, and the headline purity and water limits are effectively the same.
Technical and industrial grade
This is where care is needed. “Technical grade” is a commercial description with no fixed technical meaning. In the UK it usually denotes material that meets bulk trade purity but is sold with a reduced test panel, or recovered and redistilled material, or product blended from more than one source. Any of those may be entirely appropriate for your process. None of them is a specification.
The useful line here, and one a distributor's own site would not print: if a supplier cannot tell you which specification their technical grade is tested against, the honest reading is that the answer varies by batch. That is fine for a fuel blend or a wash solvent. It is not fine for anything where a process deviation is expensive to diagnose.
Analytical grades
HPLC and gradient grades are specified on properties that have nothing to do with bulk trade. Ultraviolet absorbance at a series of wavelengths, residue after evaporation, and a gradient elution test that checks for baseline artefacts. A published gradient grade specification typically shows purity by gas chromatography of at least 99.9%, water at or below about 0.02% and evaporation residue at or below a few milligrams per litre, with absorbance limits tightening across the ultraviolet range.
What a bulk certificate cannot tell you is whether the material will produce a clean baseline. An impurity present at a level far below any IMPCA limit can still absorb strongly at 210 nm and destroy a low-level assay. This is the clearest case on the whole site of purity and fitness for purpose being different questions.
Pharmacopoeial material
Methanol supplied against a pharmacopoeial monograph such as USP–NF, BP or Ph. Eur. is certified through a controlled quality system with the documentation trail that implies. In finished pharmaceutical products methanol itself is treated as a residual solvent under ICH Q3C, where it is a Class 2 solvent with a permitted daily exposure of 30 mg per day and a concentration limit of 3,000 ppm. That is the number that usually drives the specification decision upstream.
What each grade controls
| Grade family | Defined by | What it controls beyond purity | Relative cost | Typical use |
|---|---|---|---|---|
| IMPCA reference spec | IMPCA, currently version 10 | Water, acetone, ethanol, chloride, iron, sulphur, acidity, colour, distillation range, permanganate time, non-volatile matter | Baseline | Bulk industrial: resins, solvents, fuel, water treatment |
| Grade AA | US Federal Spec O-M-232 | Broadly the same parameter set; commonly certified alongside IMPCA | Baseline | Same as above, often where a US-origin specification is inherited |
| Technical / industrial | Supplier's own product sheet | Varies. Frequently a reduced test panel | At or below baseline | Fuel blending, cleaning, de-icing, general degreasing |
| HPLC / gradient | Supplier specification against analytical criteria | UV absorbance across the ultraviolet range, evaporation residue, gradient elution baseline test | Far above baseline | Chromatography, spectroscopy, trace analysis |
| Pharmacopoeial | USP–NF, BP or Ph. Eur. monograph | Monograph identity and purity tests plus GMP-grade documentation | Far above baseline | Pharmaceutical manufacture and regulated laboratories |
Work from the failure mode
The right question is not “how pure does it need to be” but “which contaminant would hurt”. Water is the usual answer in chemical synthesis and in fuel applications, for different reasons. Chloride matters where stainless steel is under stress in the presence of the liquid. Carbonyl compounds such as acetone matter where a downstream analysis or reaction is sensitive to them. Non-volatile matter matters where the methanol is evaporated and the residue stays behind.
Application pages on this site state the grade each process typically calls for and the impurities it is sensitive to. Formaldehyde and resins and industrial solvent use are the two most commonly relevant to UK industrial buyers, and wastewater denitrification is the clearest example of a large-volume application that is genuinely tolerant.
Where low-carbon fits
Certified bio-methanol and e-methanol are not a grade. They are conventional methanol with a certification trail attached, and they are supplied against the same IMPCA limits as fossil-route product. The premium buys the certificate, not the purity. ISCC certification and mass balance covers what the certificate has to say to be worth anything.
“Please quote against a named specification and confirm which one, and state whether a batch-specific certificate of analysis against that specification will be supplied with each delivery.” It removes the ambiguity in this whole page in a single line.
Is Grade AA better than IMPCA methanol?
No. They are different documents describing very similar material, and producers commonly certify against both on the same sheet. Grade AA comes from US Federal Specification O-M-232 while IMPCA is the international trade reference. Neither is a higher tier of the other. If a supplier presents Grade AA as an upgrade, ask to see both parameter tables side by side.
Can I use industrial grade methanol in a laboratory?
For rinsing glassware or general cleaning, usually. For anything instrumental, no. Bulk specifications do not control ultraviolet absorbance or evaporation residue, so material can be entirely within a bulk trade specification and still ruin a low-wavelength assay. The relevant properties are simply not measured.
What does “99.9% methanol” on a price list actually mean?
On its own, very little. It is a purity figure with no stated test method, no water limit and no impurity panel behind it. Two products both described as 99.9% can differ by an order of magnitude in the trace impurity that matters to your process. Ask for the specification the figure is drawn from.
Does bio-methanol come in a different grade?
No. Certified bio-methanol is supplied against the same trade specifications as conventional methanol and is chemically identical. What differs is the certification and chain of custody documentation, which is what the premium pays for.
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