What does 99% purity actually mean?
It means that of everything the detector could see, 99% of the chromatographic area was the main peak. Our purity layer is RP-HPLC 214nm (USP 621), and 214 nm is the wavelength where the peptide bond absorbs. The number is a ratio, and the denominator is everything that absorbed at that wavelength and eluted during the run. That is the right denominator for related peptide impurities and it is the wrong denominator for anything without a chromophore.
How can a vial be 99% pure and still under-dosed?
Easily, and this is the single most common misreading in this market. Purity is a proportion; content is a quantity. A vial containing 5 mg of very clean peptide against a 10 mg label claim is 99% pure and half the labelled dose. Salts, counter-ions such as TFA, residual moisture and bulking agents do not absorb at 214 nm, so they never enter the purity denominator and cannot pull the percentage down. That is why net peptide content is a separate measurement rather than a second view of the same one.
What is net peptide content?
Quantitative HPLC vs reference std. It is the milligrams of the actual target compound in the vial, with moisture, salts and counter-ions stripped out, compared against the label claim. It is not the fill weight of the powder, and the gap between the two is routinely large.
Why does the identity result show ppm as well as daltons?
Because a mass error in daltons is not comparable across compounds. A 1.0 Da error is enormous on a 161 Da small molecule and unremarkable on a 4813 Da peptide. The ppm figure normalises the error against the molecule's own mass, so it is the number that tells you whether the identity is tight or merely inside a generous absolute window.
What is a mass basis, and why does it matter?
A molecule has two commonly quoted masses: the monoisotopic mass, using the most abundant isotope of each element, and the average mass, weighted across natural isotope abundance. They are different numbers for the same molecule. Comparing an observed monoisotopic reading against an average theoretical value produces an error that belongs to the reference rather than to the vial. Our certificates state the basis so the comparison is checkable.
Does a passing sterility screen mean the vial is safe to inject?
No, and nothing on our certificates should be read that way. Our testing is for research use. Separately from that: a rapid microbial screen is not a compendial sterility release, and sterility does not cover bacterial endotoxin, which is a heat-stable cell wall fragment that survives sterilisation. Sterility and endotoxin are two different questions needing two different tests.
What does not detected mean on the fentanyl screen?
Not present above the method detection limit, for the analogs on the target list. A targeted screen cannot rule out an adulterant it was not looking for, and we state the limit rather than implying an absolute.