ETHEREALPEPTIDES

Testing

What we measure, and what the number actually means

Two analyses run on every lot by a laboratory with no stake in the result: chromatography to establish how pure the material is, mass spectrometry to establish that it is the right molecule. Both are published here before the lot is listed.

Purity claims circulate in this market with no method attached to them, which makes them impossible to compare and easy to invent. This page exists so the figures on our product pages can be read properly — what the assays do, what the percentage covers, and, just as importantly, what it leaves out.

None of it is proprietary. The techniques below are standard analytical chemistry, taught in any undergraduate instrumental analysis course. The only thing a supplier controls is whether they commission the work, and whether they show you the result.

Method one

High-performance liquid chromatography

HPLC answers one question: how much of this sample is a single component, relative to everything else the instrument can see?

A weighed portion of the lot is dissolved and pumped at high pressure through a column packed with a stationary phase — for peptides, typically a reversed-phase C18 material. A mobile-phase gradient carries the sample through it. Components with different affinities for that stationary phase move at different speeds, so a mixture that entered the column together leaves it separated in time.

A detector at the column outlet records absorbance continuously. For peptides the wavelength is usually 214 or 220 nm, where the peptide backbone itself absorbs. The output is a chromatogram: signal plotted against time, with each separated component appearing as a peak. The time at which a peak appears is its retention time; the area underneath it is proportional to how much of that component was present.

Purity is then reported as area percent — the area of the main peak divided by the total integrated area of all peaks, times one hundred. A result of 99.2% means the principal component accounted for 99.2% of the detected, integrated signal. The remainder was other peaks: process-related impurities, deletion or truncation sequences, oxidation products, residual reagents.

Method two

Mass spectrometry

Mass spectrometry answers a different question: is the dominant component the molecule the label names?

The sample is ionised — for peptides, almost always by electrospray, which is gentle enough to leave large molecules intact — and the resulting ions are separated by their mass-to-charge ratio. Electrospray tends to produce a series of multiply charged ions from the same molecule; deconvoluting that series yields the molecular mass.

That measured mass is compared against the theoretical mass calculated from the compound's formula or amino-acid sequence. Agreement within the instrument's tolerance is strong evidence of identity. Disagreement is diagnostic in its own right: a mass low by one residue points to a deletion sequence, a shift of roughly +16 suggests oxidation, and a mass bearing no relation to the expected value means the vial does not contain what the label says.

Where a certificate lists LC-MS, the two techniques were run coupled: the chromatograph separates the mixture and feeds each fraction into the mass spectrometer as it elutes, so identity can be assigned peak by peak rather than to the sample as a whole.

Purity without identity is a precise measurement of an unknown substance. Identity without purity says nothing about what else is in the vial.

Reading the number

What a purity percentage does and does not cover

Chromatographic purity is a relative measurement, not an absolute statement about the contents of the vial. Four qualifications matter, and any honest supplier will state them plainly.

It only counts what the method can see

Area percent is calculated across species that dissolve in the mobile phase, elute from the column within the run time, and absorb at the detection wavelength. A contaminant failing any of those three conditions contributes no peak, and therefore no area — it is invisible to the calculation rather than counted as zero. This is why confirming identity by a second, orthogonal method is not optional.

It is not the same as net peptide content

A lyophilized peptide is not pure peptide by mass. Residual water, which these materials readily reabsorb from air, and counterion salt left over from purification both add to the weight in the vial without appearing as chromatographic impurities. A lot can be 99% pure by HPLC and still be meaningfully less than 99% peptide by mass. The two figures answer different questions, and net peptide content requires its own assay. Where a certificate does not list one, none was run.

Decimal places are not a ranking

Integration involves judgement about where a peak begins and ends, and repeat injections of the same sample do not return an identical figure. The difference between a 99.2% and a 99.4% result generally sits inside method variability. Treat a purity figure as a threshold that was cleared, not as a score for sorting suppliers.

It describes one lot, on one day

A certificate is a snapshot of the material sampled at the moment it was sampled. It says nothing about a different lot of the same compound, and nothing about how the material was handled afterwards. That is the entire reason lot codes exist, and the reason ours are printed on the vial and searchable below.

Limits

What a certificate of analysis is not

A COA is a record of specific tests, run on a specific sample, by a specific laboratory. It is not a general warrant of quality, and it is emphatically not a clearance for any particular use. Unless a test is named on the document, it was not performed.

  • It is not a sterility or endotoxin statement. Neither HPLC nor mass spectrometry detects microbial contamination or bacterial endotoxin. Those are separate assays with separate documentation.
  • It does not cover residual solvents, heavy metals or bioburden unless those methods appear in the methods list.
  • It does not identify the impurities. Area percent quantifies the fraction that was not the main peak. Naming those related substances requires further characterisation work.
  • It is not a stability study. A certificate records material as tested — not how it behaves over the following two years, and not how it behaves once it has left our control.
  • It is not a regulatory approval or a safety finding. No certificate on this site, or any site, constitutes evaluation by the FDA or any comparable authority, and none of it makes a compound suitable for administration to a person or an animal. See the research use only policy.

Field guide

How to read one of ours

Every certificate we publish carries the same six fields. They map one-to-one onto the columns of the library below, so a lot code taken off a vial label can be traced to its document in a single search.

FieldWhat it tells you
LotThe manufacturing batch this certificate belongs to. Printed on the vial label and the packing slip. A certificate is valid only for its own lot.
PurityChromatographic purity as area percent, from the HPLC run — read alongside the four qualifications set out above.
MethodsEvery assay actually performed on this lot. HPLC and MS are the floor; LC-MS, NMR, Karl Fischer and elemental analysis appear where they were commissioned.
Tested onThe date the laboratory ran the analysis — not the date we received the material, and not the date it was listed.
LaboratoryThe independent facility that ran and signed the work. We do not perform our own release testing.
CertificateThe document itself, unedited. It stays published after the lot sells out so prior work remains citable.

If a lot is missing

Certificates are published as the laboratory returns them, so a lot that has just arrived may reach the library a day or two ahead of its listing. If you are holding a vial whose lot code returns nothing here, send us the code and we will forward the document directly.

The evidence

Certificate library

Every certificate we hold, including lots that have sold out. Search by compound, lot code, laboratory or assay method; sort by any column.

93 certificates published · sorted by tested descending

A note on the linked documents: the certificate PDFs behind these links are structural placeholders. The lot codes, purity figures, dates, laboratories and methods shown in the table are the fields the real certificates will populate, and the viewer is finished — but the signed PDFs themselves are pending delivery from the testing laboratory. Treat the linked files as format samples until this note is removed.