How Alphex tests every batch: synthesis, RP-HPLC and the COA
The verification pipeline every Alphex research peptide batch passes before vialling: SPPS, RP-HPLC at 220 nm, then the batch-matched COA.
"Lab tested" appears on nearly every research peptide website. It rarely says which tests, to what threshold, on which batch, or by whom. This note sets out exactly what Alphex does between synthesis and the vial arriving on your bench, so that the claim on the product page means something specific and checkable.
Stage one: synthesis to a defined target
Peptides are built by solid-phase peptide synthesis (SPPS): the chain is assembled one protected amino acid at a time on a resin support, then cleaved and deprotected. The theoretical molecular weight of the target sequence is fixed before synthesis begins and is the reference every later test is checked against. Synthesis is carried out under controlled humidity because several of the intermediates and the final lyophilised product are hygroscopic.
What can go wrong at this stage: incomplete coupling produces deletion sequences (a residue missing), incomplete deprotection leaves protecting groups on side chains, and side reactions such as oxidation of methionine or tryptophan create related substances. These are the impurities the later stages are designed to detect and remove.
Stage two: reverse-phase HPLC purity
Crude peptide is purified by preparative reverse-phase HPLC and then analysed by analytical RP-HPLC. The analytical run uses a C18 column with a water/acetonitrile gradient containing 0.1% TFA, detection at 220 nm (the peptide bond absorbance), against a reference standard for the compound. The main peak is the target; each additional peak is integrated and reported as an area percentage.
Our acceptance threshold is 99+% purity. The industry default for "research-grade" material is around 98%. Reaching 99+% consistently means running longer purification gradients and cutting fractions more tightly, which costs yield. We think that cost is worth absorbing because related substances at the 1 to 2% level are structurally close to the parent and can read as the parent in binding and activity assays.
The chromatogram, integration table and method conditions are printed on the COA. If you want to see how a chromatogram should be read, and what a shoulder on the main peak means, our note on how to read a research peptide COA walks through it.
Stage three: mass spectrometry identity
Purity tells you how much of the sample is one thing. It does not tell you what that thing is. Identity is confirmed by electrospray ionisation mass spectrometry (ESI-MS). The observed mass, deconvoluted from the multiply-charged ion series, must match the theoretical molecular weight of the sequence within 1 Da. A batch that passes HPLC but fails MS is rejected: it is pure, but it is not the compound.
A note on water and counter-ion
Lyophilised peptides retain some water and carry a counter-ion (TFA or acetate) from purification, so gross vial weight is not the same as net peptide content. Our COA reports HPLC purity; it does not include a water-content or endotoxin assay. Researchers who need net peptide content for a concentration-critical assay should account for this in preparation, and we are happy to discuss on request.
What goes onto the Certificate of Analysis
The results from all three stages are recorded on the COA for that batch:
- Batch number, matching the vial label
- Test date as reported by the laboratory
- RP-HPLC purity with the full chromatogram, integration table and method conditions
- The issuing third-party laboratory's name and address
The COA is published in the COA library, so you can read it before you order. Search it by the batch code printed on the vial label.
Storage between testing and dispatch
Passing the tests is only useful if the material that reaches you is the material that was tested. Vials are stored sealed at minus 20 C in UK stock, and shipped vacuum-sealed by tracked next-day courier with same-day dispatch on orders placed before 2pm, Monday to Friday. Light-sensitive compounds are packaged to exclude light. Our note on peptide storage, reconstitution and shelf life covers what to do on arrival.
Verification after delivery
If a vial is independently tested and returns a purity below the shipped threshold, we will re-test a returned sample by HPLC and replace or refund at no cost. That guarantee is only possible because the batch record exists. It is also, we think, the fairest way to settle the "lab tested" question: not by asking you to trust the claim, but by making it checkable and standing behind it.
Related
- What "99+% HPLC-verified purity" actually tells you
- Choosing a UK research peptide supplier: the 12-point checklist
- Alphex research peptide catalogue
Sources and further reading
- ICH Quality Guidelines (Q1A stability, Q3A/Q3B impurities, Q6 specifications): the reference framework for purity, impurity and stability testing
- Alphex Limited, Companies House register (company 16674899)
All Alphex products are supplied for laboratory and in-vitro research only and are not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 23 June 2026, last reviewed 16 August 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.