How We Test Every Lot

How we test every lot

Research peptides are only as good as the paper trail behind them. A vial is a white powder; without testing, you cannot tell a 98%-pure target sequence from a 60%-pure sequence contaminated with truncation products or a completely different peptide. That is the problem lot-level testing solves — and it is the reason we treat testing as a non-negotiable line item on every purchase order, not an occasional QC spot-check.

This page explains, in plain language, what we test for, how the testing is done, and what happens when a lot fails. If any of this is unclear or you want to see the underlying data for a specific lot, email support@prescottbiopeptides.st with the lot number.

1. Why lot-level testing matters

A “lot” is a single synthesis batch. Two lots of the same peptide, even from the same manufacturer, can differ in purity, identity, salt form, and residual solvent content. Testing at the SKU level (once per product) tells you nothing about the vial actually in your hand. Testing at the lot level tells you exactly what came out of the run that produced your specific vial. We refuse to sell any vial whose lot has not been independently assayed. There is no “trust the manufacturer’s spec sheet” exception.

2. HPLC purity — what it measures

High-performance liquid chromatography is the primary purity assay. A small sample of the peptide is dissolved and injected into a chromatograph, which separates the components by how strongly they interact with a stationary phase under a moving solvent gradient. The output is a chromatogram: a plot with time on the x-axis and detector signal on the y-axis. Each peak is a distinct chemical species; the area under each peak, relative to the total, gives the purity percentage of the main compound.

• What “purity” means in context. A purity of 98% means that, of all detectable species in the sample, 98% by peak area is the target peptide. The remaining 2% is typically truncation products (missed amino acid couplings), deletion sequences, or residual synthesis reagents.
• Our acceptance threshold: 98.0% or higher. Lots below 98.0% purity are rejected outright — the vials never enter our inventory. There is no “close enough” fallback.
• Reading a chromatogram. The main peptide peak should dominate; small ancillary peaks are normal, but no ancillary peak should exceed 1% of total peak area for a passing lot. Every COA we publish includes the chromatogram, not just the summary purity number.

3. Mass spectrometry identity — what it confirms

Purity tells you how clean the sample is. It does not tell you what the clean sample actually is. Identity confirmation is the job of mass spectrometry: the sample is ionized, the ions are separated by mass-to-charge ratio, and the observed molecular weight is compared to the theoretical weight of the target peptide sequence.

• Why identity matters even when purity is high. A 99%-pure sample of the wrong peptide is worthless — worse than worthless, because the customer is likely to use it and produce misleading data. Mass spec is the check that catches wrong-sequence errors, wrong-salt-form errors, and post-synthesis modifications the manufacturer forgot to mention.
• What we look for. Observed monoisotopic mass within 0.1 Da of theoretical, matching charge-state distribution, and no unexplained satellite peaks in the deconvoluted spectrum.
• Every COA includes the mass spec trace, not just a “pass/fail” annotation.

4. Third-party lab

Our current third-party testing lab is Testides. The lab is independently accredited and has no financial relationship with our peptide manufacturers. Its full name, accreditation number, and contact information appear on every certificate of analysis. Independence matters: if the lab that manufactures the peptide is also the lab that tests it, you are relying on the same organization to grade its own homework. We do not accept manufacturer-supplied COAs as a substitute for third-party data.

5. How to read a Prescott COA

Every certificate of analysis we publish contains the same standard sections in the same order:

1. Header — SKU, lot number, manufacture date, retest date, and third-party lab name.
2. Identity confirmation — theoretical vs. observed molecular weight, mass spec trace, pass/fail annotation.
3. Purity by HPLC — main peak purity percentage, full chromatogram, gradient conditions, and column details.
4. Appearance — physical description (white lyophilized powder, off-white, etc.), reconstitution guidance.
5. Handling and storage — recommended storage temperature and reconstituted stability window.
6. Signature block — analyst name (or ID), date signed, lab stamp.

If any section is missing from a COA you have received, treat it as a failed COA and email support — a complete document is a hard requirement.

6. Failure protocol

When a lot fails testing, the outcome is not negotiable and there are no “reprocessing” workarounds:

• Fails purity threshold (under 98%) — the lot is quarantined and returned to the manufacturer or destroyed. Vials never enter shippable inventory.
• Fails identity confirmation — same quarantine + return path. Additionally, the manufacturer batch record is reviewed and, in repeat cases, the manufacturer is dropped from our supplier list.
• Passes lab testing but fails our incoming visual QC (leaky vials, damaged caps, contaminated batch) — the affected units are pulled and either returned or destroyed at our cost.

We publish annual failure statistics on request. Transparency about failure rates is not a marketing exercise — it is the only credible way to demonstrate that we actually test at the volume we claim to.

Frequently asked questions

Can I request the raw chromatogram for a specific lot?

Yes. Email support@prescottbiopeptides.st with the lot number (visible on your vial label and on the packing slip). We will send the PDF chromatogram and the mass spec trace as they were delivered by the lab, unedited. Turnaround is one business day.

What if I want a lot re-tested independently?

You are welcome to send a portion of your vial to any third-party lab of your choosing. If the re-test comes back below 98% purity for a lot we shipped, we will refund the order in full, ship a replacement from a different lot at our cost, and pay the reasonable cost of the re-test up to the lot’s per-vial price. Bring us the failing chromatogram — we take our own testing failures more seriously than any customer complaint.

Do you test for endotoxin, sterility, or residual solvents?

Standard HPLC + mass spec testing does not measure endotoxin, sterility, or residual solvent content. These are separate assays. Endotoxin testing is not routine for lyophilized research peptides because handling and reconstitution are downstream of our packaging; if your research requires a low-endotoxin lot, contact sales for a custom order with the additional assay included. Residual solvent screening is available on request for wholesale quantities.

What is the “retest date” on the COA?

The retest date is the date by which the lot should be re-assayed to confirm continued potency and identity. Lyophilized peptides stored per COA guidance are generally stable well past the retest date, but the retest date is our internal trigger to pull remaining inventory and re-run HPLC + mass spec before continuing to ship from that lot. Lots that pass re-test are re-released with an updated COA. Lots that fail are destroyed.

Why don’t you show batch-level testing pass rates on the site?

We plan to. Publishing aggregate pass-rate statistics is on the roadmap for the current quarter. The tricky part is that raw numbers can be misleading (a 100% pass rate looks best but usually means the operator is either not testing many lots or not being honest about failures). We are building the presentation so the data is contextual, not just a marketing badge.