Glutathione purity is the single most important number on a certificate of analysis. Aim for 98% or above. Anything below that in a research-grade product is worth examining before you proceed.
What glutathione purity means on a COA
A certificate of analysis (COA) is a test report from an analytical lab. It lists what is in the vial and how much of it is the compound you actually want.
For glutathione, purity is usually measured by HPLC — high-performance liquid chromatography. The machine separates everything in the sample and reports back what percentage, by weight, is glutathione versus everything else. Those "everything else" substances are called impurities, and they include leftover starting materials from synthesis, breakdown products, and water.
A result of 99%+ is genuinely high purity. A result of 98% is acceptable for most research. Anything below 95% should prompt you to ask what the other five-plus percent is, because that is a meaningful fraction of what you are working with.
One number to watch alongside purity is water content. Glutathione absorbs moisture from the air easily. A COA should show a separate water content test — usually done by a method called Karl Fischer titration — so you know how much of the weighed powder is actual glutathione versus absorbed moisture. If the COA only gives one purity figure with no mention of water content, the real glutathione fraction could be noticeably lower than advertised.
What "ultra high purity" actually means
High purity glutathione and ultra high purity glutathione are marketing terms, not regulated categories. There is no official threshold that earns either label. In practice:
- High purity in the research space usually means ≥98% by HPLC
- Ultra high purity typically means ≥99%, sometimes ≥99.5%
When you see those phrases, ignore the label and look at the actual number the COA reports. A product calling itself ultra high purity with a COA showing 97.2% is just marketing. A product with no label but a COA showing 99.4% is the more analytically sound choice.
How to read an L-glutathione COA line by line
L-glutathione and glutathione refer to the same compound. The "L" describes the structural form of the molecule. All glutathione intended for research should be the L form. The COA should confirm this under identity testing, usually via HPLC retention time or mass spectrometry (MS), which identifies the molecule by its exact molecular weight.
Here is what a complete L-glutathione COA should include:
| Test | What it checks | What to look for |
|---|---|---|
| HPLC purity | % of sample that is glutathione | ≥98%, ideally ≥99% |
| Water content | Moisture absorbed into the powder | Typically under 8% |
| Identity (MS or HPLC) | Confirms it is actually glutathione | "Conforms" or correct molecular mass |
| Heavy metals | Lead, arsenic, mercury, cadmium | Should be below trace levels |
| Residual solvents | Leftover chemicals from synthesis | Should meet standard limits |
If a COA is missing the identity test, you have a purity number but no confirmation the compound is glutathione at all. That matters for analytical work.
Glutathione 1500mg COA: what the stated amount has to do with it
People searching for a glutathione 1500mg COA are usually looking at a specific product — often a research vial at a stated quantity — and want to confirm what they are actually getting. The COA does not change based on quantity. A 1500mg vial with 99% purity contains approximately 1485mg of glutathione and 15mg of impurities. A 1500mg vial with 94% purity contains approximately 1410mg of glutathione — a 75mg shortfall. At larger quantities, a purity difference compounds.
The practical check: take the stated quantity, multiply by the purity percentage, and that is your actual glutathione content. For research reproducibility, this matters every time you prepare a solution.
Where the COA comes from
The issuing lab is as important as the numbers. A COA produced by the same company that sells the product carries less weight than one from an independent third-party lab. Look for a named lab, a report date, a batch number, and a reference range for each test. Those details show the report belongs to a specific production lot, not a single test done once and reused across every batch.
The batch number on the COA should match the batch number on your vial or packet. If they do not match, the report does not correspond to what you received.
A solid glutathione COA shows HPLC purity at 98% or above, a separate water content figure, an identity confirmation, and a named independent lab. Those four things together give you a reliable picture of what you are working with analytically.
NXT Labs products are sold strictly as research chemicals for in vitro research, laboratory testing and analytical purposes only, and are not intended for use in any human or animal application.
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