How every batch is tested before it is listed.

An RP-HPLC trace plots detector response against retention time. The target sequence elutes as the dominant peak; everything else — truncated sequences, deletion products, scavenger adducts, residual solvent — appears as smaller peaks before or after it. Purity is the area of the main peak divided by the summed area of all integrated peaks, expressed as a percentage. A single sharp, symmetrical main peak with a flat baseline is what a clean lot looks like; shoulders or a broad tail indicate co-eluting related substances.

220 nm targets the peptide bond itself, so every residue contributes to the signal. 280 nm targets aromatic side chains — tryptophan, tyrosine, phenylalanine — which many research peptides contain in small numbers or not at all. A sequence with no aromatic residues is effectively invisible at 280 nm, which is why 220 nm is the standard wavelength for peptide purity work.

HPLC quantifies how much of a sample is the main component; it says nothing about what that component is. Electrospray-ionization mass spectrometry measures the molecular mass of the eluting species and compares it against the theoretical mass of the intended sequence. A lot can be 99% pure and still be the wrong peptide — running both methods closes that gap, which is why identity and purity are reported as separate lines on every certificate.

They measure different things and both appear on our certificates. Chromatographic purity (RP-HPLC) describes the proportion of peptide-related material that is the target sequence. Peptide content (nitrogen determination or amino-acid analysis) describes how much of the vial's total mass is peptide at all, with the remainder being counterion salt, residual water, and solvent. A vial can be 99% pure by HPLC and roughly 80% peptide by mass — that is normal for a lyophilized acetate salt, not a discrepancy.

Concentration equals mass divided by volume. Reconstituting a 10 mg vial with 2 mL of bacteriostatic water yields 5 mg/mL; the same vial with 1 mL yields 10 mg/mL. Working in mg/mL and recording the exact diluent volume in your lab notebook keeps subsequent dilution calculations traceable. This is solution-preparation arithmetic for laboratory use and is not guidance on administering anything.

Most synthetic peptides are purified as acetate salts, so a portion of the vial's mass is counterion rather than peptide. We report acetate content per batch (specification ≤ 15.0%) precisely so that laboratories doing mass-based calculations can account for it. If your work requires net peptide mass rather than gross vial mass, use the peptide content figure on the certificate.

Bacterial endotoxins are measured by LAL assay and reported in endotoxin units per milligram; a low result indicates the material was handled under controlled conditions during synthesis and fill. Water content is measured by Karl Fischer titration — excess residual moisture accelerates degradation of a lyophilized powder in storage, so a low figure is a stability indicator as much as a purity one.