Area percent is not mass percent
RP-HPLC–UV purity is reported as area percent at a single wavelength. A co-eluting impurity with weak absorbance at 214 nm is under-counted; one with strong absorbance is over-counted. Where we suspect co-elution we say so in the impurities paragraph and name the retention time. Area percent also says nothing about how much of the powder is peptide. The counter-ion (trifluoroacetate or acetate), water and any bulking excipient do not absorb at 214 nm and are invisible to a purity figure; a 99% area powder is commonly 75–90% peptide by mass. Mass per vial, with water content, is the test that answers that question, and the certificate prints the balance: peptide, water, counter-ion at its stoichiometric maximum, impurities, and what is left.
Identity is confirmation, not discovery
LC–MS confirms that a named molecule is present at the expected mass. It does not survey for what else may be there. It cannot distinguish stereoisomers (a D- for an L-amino acid) or sequence isomers, which have exactly the same mass. Chromatography separates some of them, and where we hold a reference standard its retention time is printed with the system suitability as the evidence for which isomer is present; where we do not, identity rests on mass alone.
Results describe the sample received
A result describes one container at one moment. It says nothing about other vials in the lot, about what the seller ships next week, or about how the material was handled after it left us.
A purity number is not a safety finding
We measure composition. We do not assess whether a substance is safe, effective, or lawful to possess or administer, and no result from us should be read as clearance to use anything.
Sterility and endotoxin are different questions
An endotoxin result within limits does not establish sterility, and a sterile preparation can still carry endotoxin. Ordering one does not answer the other.
Corrections and retractions
Measurements carry uncertainty. When an error is found in an issued report, a correction is published as a new record, the original is marked retracted rather than deleted, and both remain reachable at their original addresses for the life of the register.
A verdict only against a specification you supply
We set no specification of our own except the identity criterion. Where you supply one, or the vial carries a label claim, the certificate prints the measured value with its expanded uncertainty beside it and states whether the value meets it with the uncertainty included, only at the measured value, or not at all; the decision rule is printed on the certificate. Where nothing is supplied the result is reported for information and no conclusion is drawn. Identity is the one row we judge ourselves: Confirmed or Not confirmed against the 10 ppm criterion on the methods page.
What we do not measure
The counter-ion content (trifluoroacetate or acetate) is bounded by stoichiometry on the certificate, not measured; residual solvents, bulking excipients such as mannitol, elemental impurities and, for GHK-Cu, copper are not determined. Anything of that kind in the powder appears in the mass balance as “unassigned” and nowhere else.
The commitments that
make these limits enforceable, including that the register refuses to
delete a report and shows a deletion at its next integrity check, are
listed once, on the
Why Cupel page.