Peptide Sciences posts HPLC and mass spec COAs on its own site, but names no ISO 17025 lab. Learn the 4 checks that separate supplier COAs from real ones.
Short answer: Peptide Sciences publishes analytical documentation — HPLC chromatograms and mass spectrometry reports with stated purity, typically ≥99% — attached to its product listings. What it does not appear to publish, as of this writing, is an ISO/IEC 17025:2017 accreditation number belonging to an outside laboratory with no commercial relationship to the seller. That distinction is the whole question. A certificate hosted on the vendor's own domain, without a named accredited lab, a report number, an analyst signature, and a lot number that matches the vial you receive, is a supplier COA — not a third-party COA. Verify it on the current product page before you rely on this, because publishing practices change quarterly across this category. The rest of this page explains how to tell the two apart, and what neither one tells you.
The phrase gets used three different ways in this market, and only one of them is worth paying for.
Only the third removes the seller from the loop entirely. Everything else is a supplier making a claim with better evidence than a bare number on a label.
This works on any supplier's paperwork, including ours. Open the PDF and look for the following:
A purity figure without a method, a lot number, and a lab you can call is a rounding of someone's optimism.
This is where most buyer comparisons go wrong, and it applies to every supplier equally.
HPLC purity is reported as area-percent at a single wavelength. It answers one narrow question: of the material that eluted from the column and absorbed at 214 nm, what fraction was the target peak? It is structurally blind to three things:
Counterion mass. Reverse-phase purification with 0.1% TFA leaves trifluoroacetate bound to basic residues. Depending on the number of arginine, lysine, and histidine residues, TFA can account for roughly 5–20% of the dry mass in the vial. A lyophilized powder can be 99% pure by HPLC and still be well under 85% peptide by weight.
Residual water. Lyophilized material typically retains 2–10% moisture, more if the stopper seal was compromised in transit. Karl Fischer titration measures this; HPLC does not.
Non-eluting and non-chromophoric species. Anything that stays on the column, elutes in the void volume, or lacks a UV chromophore at 214 nm is invisible. Residual salts, scavengers, and some synthesis byproducts fall here.
The figure that closes this gap is net peptide content, determined by quantitative amino acid analysis or nitrogen determination. Very few catalog suppliers in any tier publish it, because it costs an extra $150–$400 per lot and it makes the headline number look worse. If two suppliers quote the same 99% and only one publishes net peptide content, you are not comparing like with like — and the one with the lower net figure may simply be the honest one.
Mass spectrometry has a parallel blind spot. ESI-MS confirms molecular mass to within roughly ±0.5 Da on a quadrupole instrument, or under 10 ppm on a high-resolution system. That distinguishes the target from a deletion sequence missing a residue. It does not distinguish sequence isomers, scrambled disulfides, or D-amino acid epimers introduced during coupling — those are mass-identical. Confirming sequence requires MS/MS fragmentation, which almost no catalog COA includes.
Naming this plainly, even though it argues against a sale.
A reasonable standing policy for a working lab: budget about 2% of annual reagent spend on independent verification, spend it on the highest-value or highest-risk lots, and audit roughly 1 in 5 new-supplier lots for the first year, then taper to 1 in 10 once a supplier has a clean record across 8–10 consecutive lots.
Ask any vendor these five questions in writing and keep the replies:
1. Is the COA lot-specific, and does the lot number appear on the vial label?
2. Who ran the assay — name and address of the laboratory?
3. Is that lab ISO/IEC 17025 accredited, and is peptide purity within its scope?
4. Do you publish net peptide content or water content, or purity only?
5. If an independent lab reports below your stated purity, what is your remedy and what is the window?
Question five separates the field. Vendors confident in their material state a policy; vendors who are not will describe testing at length and never mention what happens when it fails. Our answer to all five lives on the quality page, and we will put it in writing to any buyer who emails contact. If you are comparing several vendors on documentation practice rather than price, the pure tested peptides reviews breakdown covers what different suppliers publish and what they leave out, and quality research chemicals suppliers covers the qualification process for a lab standardizing on one source.
The honest position on the original question: Peptide Sciences documents its material, and documentation is meaningfully better than none. Whether that documentation is genuinely third-party depends on facts you can check yourself in four minutes — lot number, lab name, accreditation scope, method parameters, reachable signatory. Apply that test to every supplier you consider, this one included. The vendors worth buying from are the ones who expect you to.
Supplied strictly for in-vitro laboratory research by qualified researchers and institutions. Not a drug, food, cosmetic or dietary supplement. Not for human or veterinary consumption. Not evaluated by the FDA.
Purity, identity and lot number, documented for the exact vial you receive.