How to read a butane Certificate of Analysis
A Certificate of Analysis is the lab report behind a lot of butane. If you buy by the pallet, it is the fastest way to tell a clean, consistent supplier from one that is guessing. Here is what each line means and what to look for.
Updated November 12, 2026 · Puretane
What a CoA is, and what it is not
A CoA reports the results of laboratory tests on a specific lot (batch) of product. It is not a marketing sheet and it is not a Safety Data Sheet. The SDS describes hazards and handling for the product in general; the CoA tells you what was actually measured in one lot. A useful CoA always ties the numbers to a lot number, a sample date and the lab that ran the tests.
The lines that matter
1. Purity (hydrocarbon composition)
This is usually reported as percent n-butane, with the other hydrocarbons that were detected listed beside it, typically isobutane, propane and small amounts of pentanes. Labs commonly measure this by gas chromatography; the standard U.S. method for LP gases is ASTM D2163, which determines individual C1 to C5 hydrocarbons. Check two things: the headline purity, and whether the remaining fraction is identified. A report that says "99%" with nothing else tells you much less than one that lists what makes up the other 1%.
2. Sulfur
Sulfur compounds cause odor, corrosion and off-flavors, and some fuel-grade butane has sulfur-based odorants added on purpose. Total volatile sulfur in LP gases is commonly measured by ultraviolet fluorescence under ASTM D6667. For extraction-grade butane you want sulfur reported as not detected or in the low parts-per-million range, with the detection limit stated.
3. Moisture
Water in butane can freeze in valves and regulators and carry contaminants with it. It is reported in parts per million. Look for a number and a detection limit, not just "dry."
4. BTEX
BTEX stands for benzene, toluene, ethylbenzene and xylenes, aromatic compounds you do not want in a solvent. Each should be listed individually, ideally as not detected with the limit of detection shown.
5. Residue
Some CoAs also report non-volatile residue, the oily material left behind when the butane evaporates. ASTM has a gas chromatography method for residues in LP gases (ASTM D7756). Residue is where can lubricants and dirty transfer lines show up.
Red flags
- No lot number, or a lot number that does not match the cylinders you received.
- No lab name, or a CoA "issued by" the seller with no lab identified.
- Results with no units or no detection limits.
- The same CoA dated years ago, sent with every order.
- Purity claims with too many nines and no supporting breakdown.
What a Puretane CoA shows
Our current n-butane CoA (lot 05/14-30/2D, AIM Laboratory) reports 99.68% n-butane by weight, with sulfur not detected (under 0.1 ppm), moisture not detected (under 1 ppm) and each BTEX compound not detected (each under 0.5 ppm). CoAs are updated monthly and are available on request with your order. See the full spec sheet on our 100% n-butane page.
Frequently asked questions
Is a CoA the same as an SDS?
No. A Safety Data Sheet covers hazards and safe handling for a product in general. A Certificate of Analysis reports lab results for one specific lot.
How often should a supplier update its CoA?
Each lot should have its own results. Puretane updates its CoA monthly and provides it on request.
What test method is used for butane purity?
Gas chromatography is standard. In the U.S., ASTM D2163 is the common method for individual hydrocarbons in LP gases.