Certificates of Analysis & Lab Testing

The specification

Each product page states the specification its lot must meet before release. Most catalog peptides are specified at ≥99% by HPLC. A small number are specified at ≥98%, and multi-component blends are specified at ≥99% per component rather than as a single figure for the mixture.

The specification is the release threshold, not the result. The exact figure for the lot you receive is printed on that lot's certificate of analysis, and it is normal for it to sit above the threshold. Laboratory consumables, diluents and reconstitution supplies carry no purity specification, because the concept does not apply to them.

A specification is also narrower than it looks: it is one measurement, by one method, on one production run. The rest of this page sets out what that measurement is, what it leaves outside itself, and what documentation built on it can and cannot be stretched to cover.

What purity measures

Purity by HPLC is an area-percent figure: the area of the main peak divided by the total integrated area of every peak the detector saw, expressed as a percentage. Detection is by UV absorbance near 214–220 nm, where the peptide bond itself absorbs. So ≥99% by HPLC means that related peptide species — deletion sequences, truncations, incompletely deprotected chains, oxidised or deamidated forms, dimers — together account for under 1% of the detected signal. What ≥98% and ≥99% actually mean works through the measurement itself, and purity defines the term as a certificate uses it.

It is a relative figure, not an assay of how much peptide is in the vial. It describes peptide content relative to other peptide-related species, and says nothing about counter-ion content, residual solvent or water, which is why net peptide mass and gross vial mass are not the same number — a distinction that matters as soon as you calculate a concentration. Synthetic peptides are isolated as salts, and trifluoroacetate commonly accounts for 10–25% of gross weight depending on how many basic residues a sequence carries; acetate is the deliberate alternative where TFA would interfere. Net peptide content across research material typically runs 70–90% by mass. A 99% pure 5 mg vial therefore does not hold 4.95 mg of peptide, and the gap is a property of the formulation rather than a defect. The reconstitution calculator works from the figure on the certificate for exactly that reason, and molecular weight, moles and molarity sets out the arithmetic that the molarity calculator automates.

Where a single number misleads

An area percent is the output of a method, and the method is part of the result. Column chemistry, gradient slope, run length, detection wavelength and the integration decisions — where the baseline is drawn, whether minor peaks are integrated or cropped — all move the figure. A shallow gradient resolves a deletion sequence that elutes close to the target; a steep one can hide the same species inside the main peak and report a higher number for worse material. A wavelength chosen away from the backbone absorbance reweights species by what they happen to absorb rather than by how much of them there is.

The consequence is specific: two laboratories' purity figures for the same vial are not directly comparable, and the spread between methods can exceed the gap between a 98% and a 99% specification without either laboratory being wrong. Ranking suppliers on headline percentages, with no method stated on either document, compares typography rather than material. What is comparable is one method applied to both samples.

A figure is worth as much as the chromatogram behind it. Read for one dominant, symmetric main peak; a flat baseline, since drift inflates or deflates every area ratio; minor peaks integrated rather than cropped; a full time axis rather than one truncated before the late eluters; and a stated method — column, gradient, wavelength, run time. A single clean peak establishes homogeneity, not correctness: the wrong sequence can also be 99% pure, which is the reason purity is never reported alone. HPLC covers the separation itself.

How lots are assayed

Each lot is assayed by reversed-phase HPLC for purity, with mass-spectrometric confirmation of identity. The two answer different questions and neither substitutes for the other: HPLC resolves how much of the material is the intended species, while mass spectrometry confirms that the species is the one the label names. Why identity and purity are separate measurements goes into how each readout is produced and what it can and cannot tell you.

Assay precedes release, and the specification on the product page is the gate the result has to clear. A blend specified per component is making a claim about each peptide in the vial, so its certificate carries a figure per component and a chromatogram that resolves them, rather than one number for the mixture — a single purity figure for a multi-component vial does not describe the product. Blends versus single vials covers how that documentation should read, including why equal mass is not equal moles.

Identity by mass spectrometry

Mass spectrometry weighs the molecule. The instrument measures mass-to-charge ratios of ionised peptide, the molecular mass is reconstructed from them, and that observed mass is compared with the mass calculated from the intended sequence. Agreement within the method's tolerance — a fraction of a dalton on a modern ESI instrument, a few daltons by MALDI-TOF — is the evidence that the vial holds the molecule the label names, modifications included. Mass spectrometry and molecular weight define the two numbers a certificate should state side by side.

Two reading errors are routine. An electrospray spectrum of a single pure peptide shows several peaks — [M+H]⁺, [M+2H]²⁺, [M+3H]³⁺ — and these are charge states of one molecule, not impurities. And a theoretical mass follows one of two conventions: monoisotopic, summing the lightest isotope of each element, or average, weighting isotopes by natural abundance. Which convention a document uses has to be stated, or the comparison it invites cannot be made.

What mass spectrometry does not establish is purity. An ion count is not an amount: ionisation efficiency differs between species, so a spectrum does not quantify what fraction of the vial is the target. Intact mass alone does not establish sequence order either, because the same residues in a different order weigh the same; separating those requires fragmentation, which belongs to characterisation rather than routine release. Isobaric differences stay invisible to it — scrambled disulfides, an isoaspartate in place of an aspartate, a residue swap that conserves mass. And it says nothing about water, counter-ion, folding or whether the peptide behaves in an assay. HPLC answers how much, mass spectrometry answers what; a certificate reporting one and not the other has answered half the question.

Lot matching and comparability

The lot number on the certificate of analysis is the lot number printed on the vial label. That is the whole point of the document: a certificate that cannot be tied to the specific vial in front of you establishes nothing about that vial.

A generic or undated certificate, or one whose lot number does not appear on the label, is not lot-matched documentation and should not be accepted as such — from us or from anyone else.

A figure is only ever true of one lot

Every analytical claim attaches to a production run. Purity, identity, appearance, water content, counter-ion ratio and the shape of the impurity profile are properties of a batch, not of a product name, so two lots that both clear the same ≥99% specification can still carry different minor species in different proportions. That is why the lot number belongs in your own records next to the data it produced: when results move unexpectedly between preparations, the lot is the first variable to check, and without it recorded the comparison cannot be made at all.

The same logic limits comparison outward. Two lots, or two suppliers, cannot be ranked on headline purity unless the methods match and both documents are lot-matched; 99.1% by one method and 99.4% by another is not a quality ordering, as what purity measures sets out. Consistency across lots is a manufacturing property, and no single certificate evidences it — a document describes the run it was issued for and makes no claim about the next one. The vendor checklist places that among the other checks worth running on a supplier.

What traceability means here is narrow and verifiable: vial label to lot number to certificate. That chain is the one we can evidence, which is why it is the one we commit to.

Problems and their signatures

Most material problems are invisible on inspection — a degraded solution usually looks perfect — and each one surfaces in a different place on a document. Knowing which readout carries which failure is most of the skill in reading analytics.

Counter-ion and salt-form confusion. Symptom: every concentration in a series low by the same factor. It does not appear in the purity figure at all, because the counter-ion sits outside the area percent. It appears in the stated salt form and in net peptide content, and an unstated salt form makes a quantity result uninterpretable rather than reassuring.
Water content. A lyophilised cake is hygroscopic, and bound and adsorbed water count toward gross mass while also supplying the medium that hydrolysis and deamidation need during storage. It shows as a water-content figure where a document reports one, never in the chromatogram.
Deletion and truncated sequences. Each coupling step in synthesis is slightly imperfect, so the characteristic by-products are chains missing a residue, capped early, or incompletely deprotected. Signature: a shoulder on the main peak or a minor peak eluting close to it, with a mass short by the missing residue. These species are structurally near the target, which is why resolution matters more than the headline number — and why they are an active contaminant rather than inert filler, since a deletion sequence can retain partial affinity for the same target.
Oxidation and deamidation. Oxidation adds 16 Da per oxygen at methionine, cysteine or tryptophan; deamidation of asparagine or glutamine adds 1 Da through a succinimide intermediate, with Asn-Gly the classic hotspot. Signature: a new minor peak at a slightly shifted retention time plus a mass offset by a known increment — which is why a mass discrepancy usually names its own cause. Degradation separates the chemical routes from the physical ones.
Aggregation. Peptides denature at air–liquid interfaces, so agitation, frothing and rough transport cost intact material. Signature: loss of main-peak area and recovery, broadening, or high-mass species — not a change in appearance.
Storage and freeze–thaw damage. Each freeze–thaw cycle concentrates solutes into the shrinking liquid fraction, shifts buffer pH as components crystallise at different points, and creates ice interfaces; the loss is cumulative and invisible until an assay drifts. Freeze–thaw cycle covers the mechanisms, how to store peptides the two storage regimes, and aliquoting the practice that removes repeat cycling from the equation.

The first four are visible at release and are what a certificate is for. The last two are properties of what happens after dispatch, which no release document can reach: a purity figure at release says nothing about purity after months in a warm warehouse. Stability is verified analytically or not at all, and that verification is yours once the material is in your freezer.

Published certificates

Where we hold a lot's certificate in a form we can publish, it is posted on that product's page as a downloadable PDF with its own page showing the lot number, the issue date the document states, and nothing else we have added. The file is the supplier's, served byte-for-byte as we received it: no stamp, no watermark, no re-typesetting. An altered document would stop being evidence of anything, which is the only reason to have one.

The analysis on a published certificate was performed by the manufacturer's laboratory. We publish the document; we did not produce it and we did not run the assay, and nothing on those pages should be read as independent third-party verification of the result.

Coverage is partial. Most listings do not yet have a certificate published here, and that is a statement about this website rather than about the material: a listing without a published PDF still has a lot-matched certificate, it simply has not been posted. Treat a published certificate as a convenience, never as the test of whether documentation exists — ask, and you get it either way. Requesting a COA covers that route, which remains the one that covers the whole catalog.

Certificates are published per lot, never per product, for the reason set out in lot matching: check the lot number on whichever certificate you are reading against the number printed on your own vial. If they differ, the document is about someone else's material. Ask us for yours by its lot number and we will send it.

Requesting a COA

Certificates are available on request for any listing, before or after you order. Ask before buying and the current lot's certificate is released ahead of dispatch; ask afterwards and it is sent with the dispatch notification.

Email info@peptide-medix.com with the product and, if you already have material, the lot number from the label. There is no account requirement and no charge. If you are evaluating us as a supplier, requesting a certificate before placing an order is the correct thing to do and we would rather you did.

Reading a COA

A certificate is only useful if you read the parts that constrain your work. How to read a peptide certificate of analysis walks through a real document field by field — net peptide content against gross mass, the counter-ion, residual solvent, water content, and which figure belongs in a molarity calculation.

The two fields most often misread are net peptide content, which is the number your concentration maths needs, and the salt form, which changes the mass per mole. Certificate of analysis and TFA salt define the terms if a field on your document is unfamiliar.

Check the header before any number: the product name as written, including salt form and any modification such as an amide or a fragment range; the lot, against your label; and the analysis date. Then judge what the document omits. A purity claim with no column, gradient or wavelength cannot be checked by anyone. An identity section that says "conforms" without a theoretical and an observed mass has stated a conclusion and withheld the evidence. A chromatogram cropped before the late-eluting peaks, or a figure of 100.00%, is a document flattering itself. These are the fields to ask about — of us as readily as of anyone else.

What documents establish

Safety data sheets are not certificates

A safety data sheet is a hazard-communication document. It covers composition, hazard classification, handling and storage precautions, spill and first-aid response, and transport classification, and it is written for the people who move, store and handle a material. It describes a substance generically: it carries no lot number, no assay, no purity figure and no identity confirmation, and it is issued per product rather than per production run, so it does not change when a new lot is made.

A certificate of analysis measures one lot; a safety data sheet tells you how to handle the substance. Neither is evidence of the other, and an SDS on file is not evidence of what is in your vial. If your receiving or intake process needs one, say so when you ask for the certificate, because they are separate documents and a request for one is not a request for the other.

The honest limits

A lot-matched certificate establishes a short list of things, and establishes them well: that a named lot was assayed, by which methods, to what result; that the result met the release specification on the product page; that the measured mass matches the sequence the label claims; and that document and vial refer to the same production run.

It does not establish the rest, and the rest matters. Not the next lot, because consistency across runs is a manufacturing property rather than a document's. Not the condition of the material after dispatch, because stability is set by storage. Not biological activity — a correct mass and a clean chromatogram do not show that a peptide folds, binds or behaves in your system. Not sterility, endotoxin, water content or net peptide content unless those tests appear on the document, since a certificate reports what was run and nothing more. And not independence: the analysis is the manufacturer's, and third-party testing means something different — a laboratory with no commercial interest in the outcome, as third-party testing explained sets out, along with what an independent report still cannot show.

Documentation narrows uncertainty; it does not remove it, and a supplier claiming otherwise is selling the paperwork rather than the material. Everything described here is laboratory research material — not a drug, supplement or consumer product — and no certificate changes that classification.

If material is off-spec

We warrant that material conforms to the specification on its certificate of analysis at the time of dispatch. Material that does not meet its certificate is replaced or refunded in full.

If your own analysis disagrees with the certificate, send us the method and the data. A purity figure produced by a different method, gradient or detection wavelength is not directly comparable to ours, and the discrepancy is often in the comparison rather than the material — but we would rather examine it than dismiss it. The refund policy covers the commercial side, and terms of sale set out the warranty in full.