Two questions, two methods
A specification for a synthetic peptide answers two separate questions. Is the material the molecule it is supposed to be, and how much of what is in the vial is that molecule rather than something else? Identity is answered by mass spectrometry. Purity is answered by high-performance liquid chromatography. A report that shows one without the other has answered half the question.
HPLC: separating the mixture
High-performance liquid chromatography pushes a dissolved sample through a column packed with fine particles under pressure. Different molecules cling to the packing with different strength and leave the column at different times. A detector at the outlet records absorbance as they pass, and the result is a chromatogram: a baseline with peaks, each peak a component of the sample, each area proportional to how much of that component was present.
Purity, as reported, is the area of the main peak divided by the total area of all peaks. A single tall peak with a flat baseline is what a clean synthesis looks like. Shoulders on the main peak, or a cluster of small peaks near it, usually mean deletion sequences, truncated chains, or oxidised variants left over from synthesis. The number on the report is only as meaningful as the method behind it: the column, the solvent gradient and the detection wavelength all change what separates from what.
Mass spectrometry: confirming what the peak is
Chromatography tells you how many components there are, not what they are. Mass spectrometry ionises the sample and measures the mass-to-charge ratio of the ions. A peptide of known sequence has a calculable molecular mass, and a spectrum whose main signal sits at that mass, or at the expected multiples of it for multiply charged ions, confirms the identity of the material. A signal that is off by the mass of a single amino acid points to a missing or extra residue.
For a copper-complexed peptide such as GHK-Cu the expected mass includes the copper ion, so the spectrum also confirms that the complex formed rather than the free tripeptide alone.
GHK-Cu as the worked example
GHK-Cu is the tripeptide glycyl-L-histidyl-L-lysine bound to a copper(II) ion. It is a useful teaching case because the analysis has to establish three things: that the peptide sequence is correct, that the copper is bound, and that the preparation is free of the free peptide and of unbound copper. The histidine residue is what chelates the copper, and the resulting complex has its own characteristic absorbance, which is why a GHK-Cu report often includes a UV-visible measurement alongside the HPLC trace.
In the literature GHK-Cu is studied for its interactions with fibroblasts and with extracellular matrix synthesis in cell models. None of that research is meaningful unless the material in the experiment was what the label said, which is the entire point of the analytical step.
Reading a report critically
A lab report is a statement about one batch on one date. It should name the compound, the batch it covers, the method used, the date the analysis was completed, and the laboratory that performed it. A report missing any of those is a picture of a chromatogram, not evidence. Results belong to the batch they name and to no other, which is why a figure lifted from a report and printed on a product page tells you nothing about the vial in front of you.
Quantified Peptides publishes no purity figure of its own on this site for exactly that reason. The specification, form, and storage condition of every listing are stated in full; a number we did not measure is not.
Products in this guide
Supplied strictly for in-vitro laboratory research. Not for human or animal use. Not approved by the TGA or any regulator for therapeutic use. Nothing in this guide is advice on use, dose or outcome.
