“Isopropyl alcohol” covers four genuinely different products, and the commercial problem is that they look identical in a drum and are described almost identically on a quotation. The grades differ in water content, in trace sulfur and carbonyls, in residue and in documentation – and choosing one level too low is a quiet, expensive failure. This page sets out what actually separates them and how to pick.
The four grades side by side
| Grade |
Purity |
Water |
Distinguishing limits |
Documentation |
| Industrial |
About 99.5% |
Up to 0.5% |
Colour and residue limits looser; sulfur not specified |
COA, SDS |
| Anhydrous / high purity |
99.9% min |
0.10% max |
Carbonyl 0.01% max, sulfide 1 mg/kg max, colour 10 Hazen max, residue 0.002% max |
COA with the full impurity set |
| Pharmaceutical (USP / EP) |
Per monograph |
Per monograph |
Compendial identity and purity tests, residual solvent compliance |
Compendial COA, SDS, GMP statement |
| Electronic |
99.9% |
Very low |
Metals and particles specified at ppb and particle-count level |
COA plus metals and particle data |
What each extra grade buys you
| Step up |
What changes |
What it protects |
Where it is wasted |
| Industrial to anhydrous |
Water from 0.5% to 0.10%; sulfur and carbonyls specified |
Water-sensitive reactions, catalyst life, odour, residue-sensitive cleaning |
General degreasing and coatings where water is irrelevant |
| Anhydrous to pharmaceutical |
Compendial testing and documentation |
Licensed manufacture and audit |
Industrial use where the dossier does not exist |
| Anhydrous to electronic |
Metals and particles specified, not just organics |
Wafer and fine-assembly cleaning |
Any use where a residue film is acceptable |
How to choose, by the constraint that binds
| Your constraint |
Grade |
Reason |
| Metal catalyst anywhere downstream |
Anhydrous with the 1 mg/kg sulfur limit |
Sulfur poisons nickel, palladium and platinum catalysts at ppm levels; industrial IPA does not even test for it |
| Water-sensitive chemistry (Grignard, moisture-cure) |
Anhydrous, and check the water on arrival |
0.5% water is about 0.28 mol per litre of solvent – enough to consume a stoichiometric reagent |
| Condensation, reductive amination, acetal formation |
Anhydrous with the carbonyl limit |
Acetone and aldehydes compete in exactly these reactions |
| Cleaning where a film is a defect |
Anhydrous or electronic, residue 0.002% max |
Evaporation residue is what is left on the surface |
| Coatings and inks |
Industrial is usually enough |
Water and trace sulfur are diluted into a system that does not care |
| Licensed pharmaceutical manufacture |
Pharmaceutical grade |
The dossier requires compendial compliance and the documentation to prove it |
The mistake that costs the most
| Mistake |
How it presents |
Cost |
| Buying industrial grade for a catalysed reaction |
Catalyst activity declines over weeks; conversion drops; the cause is never obvious because nobody tested the solvent |
Catalyst replacement, lost production, and often a full investigation before the solvent is suspected |
| Buying anhydrous but storing it open |
Water climbs back above 0.1% in a humid store |
You pay for the drying and then undo it – the specification is only valid at the point of use |
| Buying pharmaceutical grade for industrial use |
No failure, just a permanent cost premium and extra documentation |
Margin, quietly, on every batch |
| Assuming “99.9%” means the same from every supplier |
Purity matches, sulfur and carbonyls do not |
Identical headline number, different fitness for purpose |
What to write on the order
| Item |
Specification to state |
| Water |
0.10% max, with the method (Karl Fischer) |
| Sulfur |
1 mg/kg max, if any catalyst or electronic contact is downstream |
| Carbonyls |
0.01% max |
| Residue |
0.002% max, for cleaning and electronics |
| Colour |
10 Hazen max |
| Grade statement |
Whether a compendial or electronic claim is being made – do not accept an implied one |
The practical summary: the price gap between industrial and anhydrous IPA is real but small compared with the cost of a poisoned catalyst bed or a failed water-sensitive batch. If your process has either, buy the grade that specifies the impurity.
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