The analytical methods behind every certificate

Separates the target peptide from process impurities by hydrophobicity and reports purity as a percentage of total peak area at a fixed detection wavelength.

Confirms identity by measuring the molecular mass of the eluted material and comparing it against the theoretical mass of the sequence.

Water content of the lyophilised solid, by titration rather than by loss on drying.

Endotoxin load, in endotoxin units per milligram, by Limulus amebocyte lysate assay, usually the kinetic chromogenic variant.

Separates by apparent molecular weight on a gel, and is used for the larger proteins in the catalogue where a reversed-phase column would denature the molecule.

Aggregate and high-molecular-weight species, reported as monomer content. For a folded protein this, not reversed-phase area, is the meaningful purity figure.

Trace metal content, including heavy metals and, where a peptide is supplied as a metal complex, the intended metal itself.

Counter-ion content, typically acetate or trifluoroacetate left over from purification.

Volatile organic solvent carried through from synthesis and purification, by headspace gas chromatography.

Peptide or protein concentration, free thiol content, total nitrogen and pH. These are the determinations that convert an area percent into an actual amount of material.

Biological activity in a cell or binding system, used where a molecule's value depends on it doing something rather than merely being present and pure.

Appearance of the lyophilised cake and of the reconstituted solution, and sub-visible particulate count where it applies.

Which analytical methods are used to test research peptides?

Reversed-phase HPLC for purity, mass spectrometry for identity, and Karl Fischer titration for water content are the core three for a synthetic peptide. Bacterial endotoxin by LAL, appearance, pH and related substances are routinely added. Larger proteins move to SDS-PAGE and size-exclusion HPLC because reversed-phase conditions denature them, and metal complexes add elemental analysis by ICP.

Does a high HPLC purity result mean the vial contains that much peptide?

No, and this is the single most misread number in the field. HPLC purity is an area percentage: the target peak as a proportion of everything the detector saw. Water, salt and counter-ion do not absorb at the detection wavelength, so they are not in that calculation at all. A vial can be 99 percent pure by HPLC and still be a meaningful fraction water and acetate by mass, which is why water content and counter-ion content are separate determinations on the same certificate.

Is the testing laboratory ISO 17025 accredited?

Confirmatory analysis is performed at a laboratory holding ISO/IEC 17025 accreditation, the international standard for the competence of testing laboratories. Worth knowing how that standard works: it is granted to laboratories, not to suppliers, so a vendor claiming to be 17025 accredited itself is describing something that does not exist unless it operates an accredited laboratory of its own. What matters is the accreditation of the laboratory doing the work, its scope, and whether the certificate number can be checked with the issuing body. All three are published on the quality and testing page.

What does a specification column mean on a Certificate of Analysis?

It is the limit agreed before the sample was run. A result is only meaningful against a specification, because the specification is what makes the result a pass or a fail rather than just a number. A certificate that reports results with no specification column has not tested anything, it has merely measured it.

Why do the test panels differ between compounds?

Because the method has to suit the molecule. Running a reversed-phase gradient on a folded protein denatures it, so its purity figure would be meaningless; monomer content by size-exclusion is the correct measure instead. A copper-bound peptide needs elemental analysis that a plain peptide does not. An identical panel across every product in a catalogue is a sign the panel was designed for appearance rather than for the chemistry.