99% purity peptide results: why 99.9% can be a warning sign, and how to read the decimals

What a 99% purity peptide result means

A purity of 99% on a peptide COA means the main peak holds 99% of the UV peak area in one HPLC run, at the stated wavelength. For a peptide sold for research, that is a normal result, not a rare one. Bachem, a peptide manufacturer, notes that research peptides are typically above 95% pure by HPLC. Published certificates cluster higher still.

So a 99% result says the batch was well purified, as most published batches are. It does not say which peptide is in the vial, how many mg it holds, or whether it carries endotoxin. Our guide to what peptide purity means covers those limits.

This report covers the top of the scale. It shows how tightly published purity results cluster, why figures such as 99.985% and labs whose results barely vary draw doubt, and what an honest high number looks like.

Is 99% purity good? It depends on the rule

Whether 99.0% passes depends on who draws the line.

Who draws the line	Rule	Does 99.0% pass?
Finnrick, Purity Focus (default public standard)	Purity of 99.5% or more	No
Finnrick, Purity Focus Strict (members)	99.8% or more	No
Finnrick, Accuracy Focus (members)	98% or more	Yes
Peptigrity, shop trust score	A shop’s average purity enters in bands; 99.0% or more gets the top band	Yes, with the same weight as 99.9%
Peptigrity, testing-labs directory	“Excellent” at 98% and above; 95% is its research-grade bar	Yes

The two sites pull in opposite directions. Under Finnrick’s default rule, the first decimal decides a pass or a fail on purity, so 99.4% fails and 99.5% passes. Peptigrity’s shop score treats 99.0% and 99.9% the same. It says it uses bands so that HPLC measurement noise of under one point cannot decide how shops rank.

Which view fits depends on how precise the number is. That question comes later in this report, and it matters most for results near a line drawn at the first decimal.

How tightly published purity results cluster

Two rating sites show how narrow the published range is.

Peptigrity. On 3 October 2026, its directory held 13,319 certificates from 34 labs, with an average HPLC purity of 99.5%. Of 13,292 published purity tests, 0.28% fell below 95%. By contrast, 7.24% of net-content tests showed underdosing. Peptigrity concludes that purity is rarely where published tests fail.

Disclosed Labs. On 4 October 2026, its lab table listed 40 labs and 6,646 COAs. For each lab it shows the average purity and its standard deviation (SD), a measure of how far results spread around the average. We looked at the 18 labs with 30 or more COAs:

• Average purity ran from 98.95% to 99.79%. Seventeen of the 18 averaged 99.0% or more.
• SD ran from 0.00 to 3.02 percentage points. The median was about 0.29 points.

Purity spread (SD) across a lab’s COAs	Labs (of 18 with 30+ COAs)
Below 0.15 points	3
0.15 to 0.49 points	9
0.50 to 0.99 points	2
1.00 point or more	4

Counts are our tally of the Disclosed Labs table on 4 October 2026. The table changes as new COAs arrive.

Why the published range is so narrow

Published COAs are a filtered set. Disclosed Labs’ methodology says real peptide testing clusters near 99–99.9%, and that vendors reject batches under 95%. Sellers publish reports for the batches they sell. In our reading, a batch that fails purity is less likely to be listed, so its report is less likely to reach a rating site.

The spread also mixes products, sellers and periods. A lab that tests many sellers’ products can be expected to show a wider spread than one that tests a few sellers’ batches. A wide spread does not prove good measurement either. It can come from poor products, or from a lab’s own errors.

The Disclosed Labs narrow-variance rule

Disclosed Labs scores labs in a Lab Credibility Index that starts each lab at 50 points and adds points for volume, vendor diversity and verification. Its methodology (version 7, dated 16 May 2026) takes 25 points off when three conditions hold together:

1. the SD of purity across the lab’s COAs is below 0.15 percentage points;
2. the lab’s COAs come from fewer than 5 vendors;
3. the lab has 30 or more COAs.

The flag is named SUSPICIOUSLY_NARROW_VARIANCE, and it applies to every COA from a lab that meets all three. Labs with a published reporting cap are exempt. The methodology’s example is a lab that never prints purity above 99.80%.

Version 7 lowered the trigger from 0.5 points in version 6. The methodology gives the reason: real purity results sit close together near the top of the scale.

Why the rule needs all three conditions

Each condition alone is weak evidence. Disclosed’s lab page gives its reasoning: labs used by many independent vendors are harder to capture, and “healthy real-world measurements vary”. The same page says suspiciously tight clustering suggests results that were passed without real checks. In our reading, the 30-COA floor keeps small samples out, and the vendor limit aims the flag at labs whose published results come from few clients.

On 4 October 2026, three of the 18 labs with 30 or more COAs had a spread below 0.15 points. We do not name them. The spread is only one of the three conditions, and the reporting-cap exemption can apply.

What the rule does not show

The rule is a statistical screen, not a finding. Disclosed describes its scores as its opinion based on the data available to it, not statements of fact. A narrow spread has honest causes too:

• Censored values. A lab that prints “>99%” for every passing sample shows a spread close to zero, whatever it measured. That is why the reporting-cap exemption exists.
• Rounding. Results printed to whole numbers or one decimal bunch together.
• One process. A lab whose few clients send the same product from one well-run process can see very similar results.

For a buyer, the flag is a reason to look at the evidence behind a report, nothing more. Our comparison of peptide rating sites covers the rest of Disclosed’s scoring.

Why a single 99.9x% result can deserve a second look

The arithmetic of the decimals

A purity of 99.985% leaves 0.015% of the peak area for every impurity together. The European Medicines Agency’s guideline on synthetic peptides, written for medicines, uses the European Pharmacopoeia thresholds: report peptide-related impurities above 0.1%, identify them above 0.5% and qualify them above 1.0%. Methods for impurities should at least support the 0.1% reporting threshold.

A third decimal place is 0.001 percentage points, one hundredth of that reporting threshold. In our reading, a digit that small reflects the software’s arithmetic more than what the method can measure.

The same guideline warns about co-eluting impurities, which leave the column together with the main peak. Where one method cannot separate all peptide-related impurities, it says further independent methods may be needed. A single short HPLC run can show one clean peak that holds more than one compound.

How very high numbers arise

Nobody has to type a number for a purity to read too high. Method choices do it:

• a short run or a steep gradient that hides impurities under the main peak;
• a chart scaled or cropped to the main peak, so small peaks never show;
• a trace that follows only the target’s mass, which cannot show impurities of other masses;
• an integration threshold set above the small peaks;
• peaks left out with no written rule.

A full report lets a reader spot each of these. Our guide to HPLC purity testing lists what a checkable purity report shows.

What published same-batch comparisons show

Published case	Product	Purity results
Peptide Critic, 13 May 2026, six reports from five labs	Retatrutide, one 10 mg kit	Every result between 99.738% and 99.93%; one lab printed “>99.80%”
Krysia’s Substack, 13 August 2026	Tesamorelin, one batch	99.985% at one lab, 97.779% at another (averages of each lab’s vials)
Same post	Epitalon, one batch	99.935% at one lab, 95.915% at another (averages of each lab’s vials)

Each is a single published case, not proof that any lab is wrong. The sources name the labs. Read together, they show two things. A very high figure can hold up across labs, as on the retatrutide kit. On the other two batches, the labs’ results differed by about 2 and 4 points, far more than any printed decimal. Our report on why labs disagree covers the causes, and our same-batch comparison report covers each case.

Honest rounding: how many digits a purity result deserves

The Guide to the Expression of Uncertainty in Measurement (GUM, clause 7.2.6) says an uncertainty usually needs at most two significant digits, and the result should be rounded to match. Take an illustration, not a test result. A purity computed as 99.4637% with an expanded uncertainty of 0.2 points (k = 2) should be printed as 99.5 ± 0.2%.

Labs differ on how much precision they claim. Krause Analytical, answering Finnrick’s method questionnaire in March 2026, wrote that industry convention is to print chromatographic purity to four significant figures. It added that no one using commercially available instruments gets close to that, and it estimates its own values as valid to two significant figures. Near 99%, two significant figures is a whole number. On that estimate, the gap between 99.4% and 99.5% is finer than that method claims to resolve.

HK Analytical’s September 2026 review of public COAs from 25 labs and one rating site’s certificate wrapper found few reports that show this:

What the purity result showed	Of 26
A measurement uncertainty with its coverage factor (k)	1
A proper peak table with areas	4
Integration settings	0
Three decimals, on at least some reports	6
A censored value such as “>99.80%”, on at least some reports	5

A censored value does not overstate precision, but it hides the number and the impurities behind it. Three decimals with no ± overstate precision. An honest high result states the number, its uncertainty and the peaks that make it up. Our guide to peptide test accuracy explains ± and k = 2.

How to check a 99.9% purity result

What you see	Why it matters	What to ask for
Three or more decimals, no ±	Digits finer than the method can support	The uncertainty, or a result rounded to it
No chromatogram, or one cut to the main peak	Small peaks cannot be seen	The full run, with the baseline visible
No peak table	The number cannot be recomputed	Area % for each peak; add them up yourself
No wavelength, or a single-mass trace	The detector may see only the target	UV at a stated wavelength, usually 214 or 220 nm
No reporting threshold	Small peaks may have been dropped	The threshold; 0.1% or lower matches the EMA reporting level
The same purity on every batch from one seller	Real batches vary	Earlier reports, a second lab, or your own test
Purity and nothing else	Purity does not show identity or dose	Identity by LC-MS and content per vial

If a report fails these checks, treat its purity as a claim, not a measurement. Our list of signs of a fake or weak COA covers the other fields, and how to read a COA walks through a whole report.

What HK Analytical does

Our purity test reports the main peak’s share of all detected peaks, in % area at the stated wavelength. Every number in the report comes with its raw data, including the chromatogram behind the purity result, so a reader can judge the decimals for themselves. The report is a signed record (an Ed25519 signature over the canonical record) that can be checked at hkanalytical.com/verify. Reports are never edited after issue: a change makes a new version and marks the old one superseded.

Each report carries our photo of the vial as received and states how the client is related to HK Analytical. Purity can be ordered with identity (LC-MS), content per vial and the safety tests in one order. Results within days of receipt. Sterility (USP <71>, 14 days) is the one test that takes 14 days, because the method incubates for 14 days. The example report shows the layout.