HPLC

High-Performance Liquid Chromatography (HPLC), specifically Reverse-Phase HPLC (RP-HPLC), is an analytical separation technique that pumps liquid solvent (mobile phase) containing a dissolved peptide sample under high pressure through a column packed with stationary phase adsorbent particles (typically hydrophobic C18 silica). Peptides and their related synthesis impurities separate based on differences in hydrophobic interaction with the column matrix, eluting at distinct retention times detected by UV spectrophotometry.

Every legitimate Certificate of Analysis (CoA) must feature an RP-HPLC chromatogram verifying chromatographic purity, typically requiring >98% for research grade and >99.5% for pharmaceutical clinical grade.

Purity figures are one of the most common selling points in online peptide marketing, and nearly all of them come from an HPLC trace. Knowing what the test measures helps you judge what a number like “99% pure” really means. The figure is usually the share of the detected signal that sits in the main peak. It describes the relative balance of a sample’s components, not whether the main peak is the right molecule or how much peptide is in the vial.

An HPLC result is only as good as the method and the lab behind it. Separation depends on the column, solvents, gradient and detection settings, and a poorly chosen method can let an impurity hide under the main peak. Regulated manufacturers develop and validate their methods and pair HPLC with other techniques such as mass spectrometry. A single chromatogram on an unverified certificate gives much weaker assurance.

Independent testing shows the gap between label and lab. When researchers bought semaglutide vials from illegal online pharmacies and analysed them with liquid chromatography and mass spectrometry, measured purity ranged from about 7.7% to 14.4%, far from the 99% printed on the labels, and endotoxin was found in every sample. A confident purity claim on a label is not the same as a verified result.

“A high HPLC purity proves the peptide is what the label says”

HPLC separates and quantifies, but a peak’s position alone is weak proof of identity. A different peptide, or the right peptide with a wrong amino acid, can still produce one clean peak. Identity needs mass spectrometry or comparison with an authenticated reference standard run under the same conditions. Purity and identity are separate questions.

“HPLC purity tells you how much peptide is in the vial”

Purity is a relative percentage of peak area. The amount of peptide present, often called content or assay, is a separate measurement that needs a calibrated reference standard. In the 2024 test purchase study of online semaglutide, the measured amount of peptide differed from the labelled amount by roughly 29% to 39%, independent of the purity figure.

“HPLC screens for everything harmful”

A standard HPLC-UV method sees compounds that separate on the column and absorb at the chosen wavelength. It does not test for bacteria, endotoxin, heavy metals or residual solvents. Those require their own tests, which is why the online semaglutide study ran separate sterility and endotoxin checks alongside its chromatography.

What does HPLC stand for?

HPLC stands for high-performance liquid chromatography. A liquid sample is pumped under pressure through a packed column, and its components separate according to how strongly they interact with the column material. For peptides, the most widely used mode is reversed-phase HPLC, which separates molecules by hydrophobicity, though size-exclusion and ion-exchange modes are also used for specific questions.

What does 99% HPLC purity mean?

It usually means that about 99% of the detected signal at the measured wavelength came from the main peak, with the remainder spread across impurity peaks. It does not confirm the main peak’s identity, the amount of peptide in the container, or the absence of contaminants the method cannot see, such as endotoxin or microorganisms.

Is HPLC the same as mass spectrometry?

No. HPLC separates the components of a sample, while mass spectrometry measures the mass of molecules to help identify them. The two are often combined as LC-MS, where each separated peak passes into a mass spectrometer. Regulated peptide characterisation typically relies on both, because each answers a question the other cannot.

Can I trust the HPLC result on a peptide certificate of analysis?

It depends on who ran it and whether it can be checked. A useful result names an identifiable laboratory, matches a specific batch, shows the actual chromatogram, and is paired with identity testing. Certificates supplied with research-chemical peptides are not part of any drug approval review, so they deserve more caution than an approved drug’s quality documentation.