Analytical reference

How every lot is analysed

Four measurements sit behind a Certificate of Analysis. Each answers a different question, and each has a limit. Knowing which question a method answers is what lets you read a certificate instead of trusting a headline number.

The methods

What each one measures

01
Purity

Reverse-phase high-performance liquid chromatography

Question it answers: what fraction of the material in this vial is the target compound, rather than truncated sequences, deletion products, residual reagents or salt?

The sample is dissolved and pushed through a hydrophobic column under pressure. Compounds leave the column at different times depending on how strongly they stick to it, and a detector records absorbance as they come off. The result is a chromatogram: a baseline with peaks. The area under the target peak, as a percentage of the total area under all peaks, is the purity figure printed on the certificate.

What it cannot tell you: RP-HPLC separates by hydrophobicity, not identity. A closely related impurity can co-elute and be counted inside the main peak. It also says nothing about whether the peak is the compound you ordered, which is what the next method is for.

02
Identity

Electrospray ionisation mass spectrometry

Question it answers: is this actually the compound it is labelled as?

The sample is ionised and the instrument measures mass-to-charge ratio. A peptide of known sequence has a known monoisotopic mass, and peptides typically carry several charges, so the spectrum shows a predictable ladder of peaks. Matching the observed mass to the calculated mass confirms identity to within a fraction of a dalton.

What it cannot tell you: mass confirms composition, not sequence order. Two peptides with the same amino acids in a different order have identical mass. For routine release testing that is an accepted limitation; sequencing is a separate and far more expensive analysis.

03
Content

Net peptide content

Question it answers: of the mass in the vial, how much is peptide and how much is counter-ion and bound water?

This is the figure most often missed. A lyophilized peptide is typically supplied as a salt, usually trifluoroacetate or acetate, and it holds residual moisture. A vial labelled 10 mg can contain meaningfully less than 10 mg of actual peptide. Net peptide content states the real fraction, and it is the number that matters when a concentration has to be accurate.

Why it matters here: the reconstitution calculator works from the labelled vial mass, because that is what is printed on the vial. Where a certificate states a net peptide content, use that figure instead for anything where the exact concentration is the point.

04
Condition

Appearance, solubility and handling checks

Question it answers: did the material survive lyophilisation and shipping in the state it should be in?

A visual and physical inspection: the cake should be white to off-white and intact rather than collapsed or discoloured, the seal and stopper intact, and the material should go into solution cleanly in the stated solvent without haze or visible particulate. Discolouration or a collapsed cake is a signal that something went wrong upstream, regardless of what the chromatogram says.

What it cannot tell you: appearance is a screen, not an assay. Material can look correct and still fail on purity, which is why it never stands alone.

Interpretation

Reading the number honestly

Three habits that separate reading a certificate from glancing at one.

Check the lot, not the product

A purity figure belongs to one lot. It is not a property of the compound, and it does not carry across to the next release. The lot number on the vial should match the certificate you are reading.

Prefer a number to a threshold

"≥98%" is a pass mark. "99.4%" is a measurement. Both are legitimate on a certificate, but only one tells you where in the range this lot actually landed. Our aggregate dataset excludes thresholds from averages for that reason.

Look at who signed it

An in-house certificate and a third-party certificate are different documents. Every certificate in our library names the independent laboratory that ran the analysis, and those laboratories are listed on the dataset page.

A certificate does establish

  • That the material in the stated lot matches the expected mass.
  • What fraction of it is the target compound by peak area.
  • Which laboratory measured it, by what method, and on what date.
  • The physical condition the material was released in.

A certificate does not establish

  • Safety in any organism. It is an analytical document, not a toxicology report.
  • Efficacy of any kind. Nothing on a chromatogram speaks to a biological effect.
  • Sterility or endotoxin status unless that test is explicitly listed on it.
  • Anything about a different lot, including the next one of the same compound.
This is the whole basis on which the catalog is sold. Material is supplied for in-vitro laboratory research only. The analytical record says what is in the vial. It does not say what the contents do, and no page on this site will.
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