HPLC and mass spectrometry on a peptide certificate: what each result is

Written 6 October 2026, last changed 7 October 2026 by the trade desk. About 4 minutes to read.

A peptide certificate reports purity by HPLC and identity by mass spectrometry, two results that answer different questions; its third, net content, is checked against the label. RP-HPLC, reverse-phase high-performance liquid chromatography, gives purity: the share of the chromatogram’s peak area, read at 220 nm, that belongs to the main peak, not less than 98.0 percent for a peptide line at International Peptides. Mass spectrometry gives identity: the measured mass against the one calculated from the formula. Neither result stands in for the other.

The HPLC result: purity

The main peak’s share of the total peak area at 220 nm. It does not say which molecule that peak is. The figure also moves with the method, which is why a specification names its method beside the limit; why two laboratories can read one vial differently is in what 98 or 99 percent purity means. The peptide lines’ specification also caps any single related substance at 1.0 percent; the certificate does not print that figure, and the desk gives it for a particular batch on request.

Why the reading is taken at 220 nm

The peptide bond itself absorbs at 210 to 220 nm, so every chain absorbs there, whatever its side chains. That matters for a chain with no aromatic residue: BPC-157 and KPV carry no tryptophan, tyrosine or phenylalanine and absorb little at 254 or 280 nm, so their purity, like every peptide line’s, is taken at 220 nm.

The mass result: identity

Whether the main component has the mass its formula gives. On our certificates the measured mass is matched to the calculated average mass, within about one unit; high-resolution figures, which the certificate does not carry, are monoisotopic. In electrospray a chain takes more than one charge state: at high resolution BPC-157 gives m/z 1419.711 as [M+H]+ and 710.359 as [M+2H]2+, and on an average-mass reading near 1420.6 and 710.8, the figures BPC-157’s page gives. The mass result does not say how much else is in the vial, and two molecules with one formula weigh the same: an epimer, the same chain with one residue’s configuration changed, weighs exactly what the target weighs.

When two peptides have the same mass

MT-2 and PT-141 sit 0.984 apart, an amide against an acid, so telling them apart takes a high-resolution mass, or HPLC run beside a reference of the other; the certificate carries neither. FDA’s GSRS files the D-lysine form of semaglutide’s acylated residue, and a chain made with that epimer weighs exactly what semaglutide weighs; telling the two apart takes HPLC run beside a reference of the epimer, which the certificate does not carry. The pairs on this list that sit close in mass are in the certificate guide’s look-alikes table.

Protein, glycoprotein and preparation lines

These lines are not released on the peptide lines’ pair of results, an HPLC area against 98.0 percent and a mass against the formula. Each one’s page names its purity method: size exclusion and SDS-PAGE for most, and reverse-phase HPLC, against the limit stated on the batch certificate, for IGF-1 LR3, IGF-DES and Insulin. Their certificates also report endotoxin, which a peptide line’s does not: which lines report it.

Applies to

This guide was written with BPC-157, KPV (lysine-proline-valine), MT-2 (Melanotan 2) and PT-141 (bremelanotide) in mind, and it holds for the other lines of their kind; the full list is on the compounds page.

Questions about the HPLC and mass results

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