What “98% by HPLC” Is a Percentage Of
It is a ratio of peak areas, not of mass. Water, counter-ion, salts and anything that does not elute are outside the number entirely.
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How research peptide identity and purity are verified, and how to read the supporting analytical documentation.
It is a ratio of peak areas, not of mass. Water, counter-ion, salts and anything that does not elute are outside the number entirely.
When a UV detector shows a flat line, the analyte is still there. Two detectors that respond to mass instead, and what their non-linear response does to a purity figure.
Dissolution solvent, injection solvent mismatch, adsorption, filtration and hours in the autosampler. Everything that changes a chromatogram before the column sees it.
The acid in the mobile phase decides whether you get peak shape or mass spectrometer sensitivity. You rarely get both, and certificates rarely say which was chosen.
It is not a property of the molecule. It is a property of the molecule on one system, that day. What it establishes, what it cannot, and why relative retention travels better.
Electrospray gives a charge envelope, not a mass. How the software works backwards to a neutral mass, and the four ways that calculation goes wrong.
Area percentage assumes every molecule absorbs the same. None of them do. What that means for truncated impurities, blends and comparing figures between compounds.
A 29-residue peptide and a 5-residue one, five to one by mass. Why ipamorelin lands between two of the larger peptide charge states, and how isotope spacing tells them apart.
BPC-157 and TB-500 are sold three ways in Canada: separately, and together in a single vial.
Proline is the only residue whose preceding bond adopts cis and trans in comparable proportions. Three consecutive ones is why a BPC-157 chromatogram looks the way it does.
A quaternary nitrogen means a charge no pH removes. Why the mass spectrum shows M+ rather than M+H, and why reading it the usual way gives a confidently wrong number.
Eighty-three residues, three disulfide bonds and fifteen possible cysteine pairings. Why intact mass is blind to the failure mode that matters most.
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