Stated plainly: 96.4% · batch certificate.
I have read the primary source rather than the summary, which has left me with more questions.
I understand the headline. I do not understand the footnotes, and the footnotes look important.
What would I need in addition before this supported a decision?
96.4 per cent is a statement about area, and the other 3.6 per cent is everything the detector saw and did not assign to your peak. Read it as 96.4 of every 100 units of peak area at whatever wavelength was used, not as 96.4 per cent of the mass in the vial. With the batch certificate attached you can at least see how the figure was produced, which is the difference between a measurement and a claim. What it still does not tell you is content: how many milligrams are actually there.
The honest answer is that the achievable range of plausible purity figures for a given vial is wider than most people expect.
Tailing factor measures peak shape, and a badly tailing peak spreads into the region where small impurities live, forcing tangent-skim integration that assigns tail area to the main peak.
| Test | Answers | Does NOT answer |
|---|---|---|
| RP-HPLC, area % | What fraction of detected material is the target | How much target is present |
| Quantified content | Milligrams of peptide per vial | What the impurities are |
| ESI-MS identity | Whether the molecular weight matches | Purity, or isomeric substitution |
| Peptide mapping | Sequence, localised to a fragment | Quantity |
| Karl Fischer | Water content of the solid | Solvent content |
| LAL endotoxin | Pyrogen load in EU/mg | Sterility |
| Sterility test | Growth in defined media over 14 days | Endotoxin, or bioburden count |
The underlying point is that retention time is sequence-specific and method-specific, so comparing your result to a supplier value using a different method is meaningless without method documentation.
The Arrhenius relationship for peptide degradation is the basis of accelerated stability testing and also governs how quickly methods drift with temperature.
Compare purity within a single laboratory on the same method, never across laboratories.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemStart from what the detector sees, because that tells you what the number means.
Temperature affects the dynamics of molecular conformation, and if a peptide has proline residues that interconvert on the chromatographic timescale, the peak will split or shoulder at low temperature and collapse at high temperature.
Mass on column affects detector linearity and peak overlap — overloading broadens peaks and hides neighbours, while underloading improves resolution but loses sensitivity.
Proline conformer interconversion kinetics are well-characterised and the half-life is of the same order as the chromatographic peak width at room temperature.
If you are ranking vendors, specify a method and have all samples tested at the same place.
The short answer is that two competent laboratories on identical material will disagree, and the disagreement is almost always explainable by method differences.
Integration of the shoulder — whether you use perpendicular drop or tangent skim — determines what area gets assigned to the main peak versus the impurity table.
Specifically, gradient slope controls resolution, and gentler slopes resolve co-eluting impurities into separate peaks — so the better method reports the worse purity number.
The practical summary: ask for the chromatogram and the method, and ignore the headline number until you have both.
edited 4 Jun 2024 by plate_count_9k — fixed an arithmetic slip in the third paragraph
Read the chromatogram before you read the number, because the number without the trace is not a measurement, it is a claim.
Sample solvent strength affects peak shape — if you inject in strong solvent on a gradient starting in weak solvent, the solvent peak can distort your main peak or create a false shoulder.
The ICH Q3A impurity thresholds and the relevant pharmacopoeial chapters all specify method validation requirements that almost no research-grade certificate claims to meet.
I would be careful about over-reading a single measurement — treat it as a data point, not as ground truth.
If you only pay for one test, pay for quantified content. Purity is the number everyone quotes and content is the number that changes what you do.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.