What happens when a batch fails
Where failures are caught, what happens to the batch, what it costs, and why a supplier that never fails a batch is telling you something.
Batches fail. A synthesis comes back at 98.4% instead of 99+%, a mass is out by more than a dalton, a chromatogram shows an impurity that should not be there. What a supplier does at that moment is the clearest test of its specification, because a threshold only means something if material is rejected against it. This note explains what happens to a failed batch at Alphex, and what it costs. All Alphex products are for laboratory and in-vitro research only.
Where a failure is caught
- Manufacturer QC. Most failures are caught before material ships to us, and the batch is repurified or remade.
- Independent testing. A sample of every batch goes to the independent laboratory before listing. This is where a failure that manufacturer QC missed, or graded differently, is caught. See testing partner independence.
- Retest of ageing stock. A batch held long enough to reach a retest date is re-run before further sale. See how often peptides should be retested.
- A customer's own analysis. Rare, and covered by the purity guarantee.
What happens next
- The batch is not listed. No sale at a lower specification, no quiet relabelling as a different grade, no clearance pricing. The specification on the site is the specification, and material that does not meet it is not sold.
- The result is reviewed with the laboratory. Is it a genuine failure or a method artefact? A borderline purity figure on a slow gradient may resolve differently on a repeat; a mass discrepancy of +22 is a sodium adduct, not a bad peptide. See what a 1 Da tolerance means and HPLC versus UHPLC.
- The manufacturer is told, with the trace, and the batch is returned, repurified or written off. Repeated failures are a supplier-selection issue for us.
- The product page shows sold out until the replacement batch passes. This is one of the reasons Alphex runs out; see why Alphex runs out.
- If any vials have already shipped from a batch later found out of specification, we contact those customers with the finding and replace or refund, and we withdraw the batch.
What it costs
A failed batch is a direct loss: synthesis, purification, vialling and testing paid for, nothing to sell, and a gap in stock while the replacement is made. That cost is part of why UK-stocked, independently tested material is priced above drop-shipped material, and it is exactly what the buyer is paying for. A supplier who never has a failure either has a very tolerant specification or is not testing every batch. See how peptide pricing works.
What a near-miss looks like
Most rejections are not dramatic. A 39-residue lipidated peptide at 98.7% with a slightly elevated unlipidated-species peak is a perfectly usable reagent by most of the market's standards and a fail by ours. We reject it because the alternative is a specification that moves to fit the stock, which is the same thing as no specification. See 98% versus 99+%.
Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They 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 27 February 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.