HPLC versus LC-MS peptide purity

Research-use notice: This article is laboratory and educational information only. It is not medical or legal advice, and it does not include how-to-use instructions. BlueNex Labs materials are research use only and are not intended for human or veterinary use. Research-use-only labelling is not a Health Canada authorization.

Publication status: Prepared for the BlueNex Labs Research Knowledge Centre. Literature and library notes checked September 24, 2026. Primary papers and the public COA library can change; verify the lot report in hand before an assay.

Peptide "purity" on a Certificate of Analysis is almost always a chromatographic area percent. Identity is almost always a mass. Laboratories often acquire both on one LC-MS instrument, and the page can look like a single verdict. It is two methods sharing a sample. This note is the batch-method overview: what each method can say, what it cannot say, and how to keep the numbers apart. For the line-by-line reading of a finished PDF, see how to read a peptide COA. For the document definition, see identity and purity answer different questions.

What area percent means

In reversed-phase HPLC the sample is injected onto a hydrophobic column and eluted with a gradient. An ultraviolet detector, commonly at 214 or 220 nanometres, draws a chromatogram. The laboratory assigns one peak to the named peptide, usually by retention time and, when MS is attached, by the mass under that peak. Purity as area percent is that peak's area divided by the total integrated area, times 100.

Area percent is not automatically weight percent. The detector response depends on the chromophore. A deletion peptide and the full sequence can have different absorbance per microgram. Residual solvents and counter-ions may not absorb at the wavelength in use, so they can be absent from the percentage while still present in the solid. Net peptide content, when a laboratory reports it, is a different assay. If the COA does not print net content, do not derive it from the area percent.

Integration rules change the percentage. A minimum-area cutoff drops small peaks from the denominator and raises the headline number. A co-eluting impurity stays inside the main peak and never appears as its own line. Read the method note for the cutoff and look at the baseline. For the manufacturing context for why deletion and truncation sequences exist, see how peptides are made, including the short account of amino-acid analysis. Amino-acid analysis checks composition. It does not replace the chromatogram.

HPLC versus LC-MS

HPLC alone answers a separation question: under these conditions, what fraction of the ultraviolet signal sat in the assigned peak? It does not prove which molecule that peak was. A wrong sequence, a capped deletion, or a closely related analogue can be chromatographically sharp.

Mass spectrometry answers an identity question: what mass was observed for the ionized sample, or for a selected peak? Electrospray is the common ion source for peptides. The spectrum is a set of mass-to-charge values. The laboratory may report a deconvoluted monoisotopic or average mass. Compare that figure with the mass calculated from the sequence, and copy any statement about adducts or salt.

LC-MS couples the two. Liquid chromatography separates the mixture, and the spectrometer samples the eluate. You may see a UV chromatogram, a total-ion chromatogram, and a mass for the main peak on one PDF. The UV area percent remains a purity figure only for the trace that was integrated. The mass remains an identity figure only for the peak it was taken from. Do not average them into one score, and do not let a passing mass excuse an unintegrated shoulder. If the report integrates the total-ion chromatogram instead of the UV trace, the percentage is a different method. Label it the way the PDF labels it.

Other methods show up on some certificates and should stay labelled as themselves. Capillary electrophoresis separates by charge and size. Amino-acid analysis reports residue ratios after hydrolysis, which will not catch a sequence swap that preserves composition. Neither is a synonym for HPLC purity. MALDI mass spectra are still mass spectra. They are not chromatograms.

Salt form, adducts, and the mass you file

A calculated mass has to state its assumptions. Free peptide, acetate salt, and trifluoroacetate salt are different species. Sodium and potassium adducts add a familiar offset. If the observed mass matches an adduct and the report says so, file the adduct. If the observed mass matches none of the species you can justify from the sequence, stop and hold the vial. A high area percent does not repair a mass mismatch.

This catalogue does not publish a house equation for converting TFA salt weight into free-peptide weight. Receivers should not invent one either. The study file gets the phrase printed on the COA. The mass section of the reading guide makes the same point beside a real library row.

What to copy from the method line

A batch method is usable in a second person's hands when the log names the technique, the detector, the wavelength or ion mode, the date, and the laboratory. "HPLC 99%" without those fields cannot be compared with the next lot. Two lots can both read 99% area percent and still have been integrated under different cutoffs. Write the cutoff down when you have it.

Worked rows in the certificates library show why the method note has to stay attached to one vial. BPC-157 10 mg, blue cap, is a mass/purity link plus an endotoxin link on the BPC-157 product page. GHK-Cu 50 mg, batch HF1F6C9, is a mass/purity link plus an endotoxin link. The endotoxin link is not a second purity method. Retatrutide on its catalogue page is three methods packages, not one: blue 10 mg, purple 20 mg, and pink 30 mg. TB-500 10 mg has a purity report at the TB-500 10 mg certificate row and no endotoxin line. The 5 mg/5mg blend report cannot be relabelled as the TB-500 method.

The Hospira listing has no library row. A method written for a peptide sample is not the method for that bottle. The shop URL says which SKU you can order. A missing row means no sample was published for that SKU. A peptide chromatogram does not fill the blank. Without a published report, there is no task identifier to record.

What a purity figure is not

It is not an endotoxin result. It is not a sterility result. It is not evidence of a particular synthesis plant, because this catalogue does not publish factory identities. It is not a Drug Identification Number. It does not travel with the peptide after someone relabels a tube. The chain of custody after receipt is the laboratory's own record, starting from the vial match below and the storage note.

Match the PDF to the vial

Batch testing means the analytical laboratory injected the lot you are holding, not a representative lot from another month. Verification means the PDF, the library row, and the physical vial are the same material. Check the sample name, the milligram fill, the cap colour, and the task identifier in the laboratory URL. A reused certificate or a neighbouring peptide's report fails that test even when the percentage looks familiar. The line-by-line reading stays on how to read a peptide COA.

If a later lot is tested by a different laboratory or a different gradient, keep the PDFs side by side rather than averaging the percentages. The endotoxin reading note is the parallel rule for a number that HPLC cannot see.

Frequently asked questions

How is an HPLC purity percentage calculated?

Under the conditions of that run, purity is the area of the assigned peak divided by the sum of the integrated peak areas, times 100. It is not a weight percent unless the report says the calculation was different.

What does LC-MS add to an HPLC chromatogram?

The chromatography still separates the sample. The mass spectrometer reports a mass for a peak, which is the identity check. A UV area percent and a mass are different results even when one instrument produced both.

Does a high purity percentage prove the sequence?

No. Co-eluting impurities can hide under one peak, and the wrong sequence can still be chromatographically clean. Compare the observed mass with the mass calculated for the named sequence.

Where are worked examples of published lots?

The certificates library links the live PDFs. This method note uses the BPC-157 10 mg, GHK-Cu 50 mg, and retatrutide rows only as examples of separate documents.

Catalogue cross-reference

Method notes stay attached to one lot. Open the library, then the matching shop URL: BPC-157 10 mg, GHK-Cu 50 mg, retatrutide, TB-500 10 mg, or Hospira bacteriostatic water.

Orders ship inside Canada only after Interac e-Transfer checkout. Sold-out SKUs remain listed and cannot be added to the cart. Match each vial to its own Certificate of Analysis when a lot is published. Research use only. Not for human or veterinary use.

Glossary notes for the words in this guide: analytical specification, impurity profile, labelled vial mass, and oxidation impurity.