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Peptide purity and testing: how a batch is released

Last changed 6 October 2026.

A batch is released or it is not. There is no partial release: a batch whose certificate does not meet its purity, net content and identity limits never ships.

In short

Purity

Not less than 98.0 percent, RP-HPLC at 220 nm.

Identity

Mass spectrometry (ESI-MS), the measured mass against the calculated one.

Water

Not more than 8.0 percent by Karl Fischer, lyophilised peptide lines.

Samples

Retained twelve months from dispatch.

From resin to shelf

Synthesis. Solid-phase peptide synthesis for the peptide lines; recombinant expression for most protein lines, purification from urine for HMG, and urine or recombinant expression for HCG; enzymatic digestion of porcine brain protein for Cerebrolysin and extraction from bovine thymus for Thymalin; chemical synthesis for the small molecules. Each line’s page says which. Raw materials are received against a specification and held in quarantine until identity is confirmed.

Purification. Cleaved from the resin and purified by preparative reverse-phase HPLC. Fractions are pooled on purity, never on yield.

Fill. Filtered, filled to the labelled content and freeze-dried in the vial, then stoppered under vacuum or inert gas and sealed. Solution lines are mixed, filtered and filled.

Testing. For a peptide line, purity by RP-HPLC, identity by mass spectrometry (ESI-MS), and net content are the certificate’s results. Related substances, water, acetate and residual solvents are the specification the batch is made to, and the desk answers for a particular batch. Protein and solution lines are tested on the methods their own pages name.

Release. A batch whose certificate meets the purity, content and identity limits is released with a batch number, and its retest date goes on the batch record. A batch that fails one of them is quarantined.

Picking. Oldest in-date batch first. The batch number is written to the packing list as the order is packed, so the paper and the register say the same thing.

The batch number

Form, month made, product code, sequence. L2607-RT30-0002: lyophilised, July 2026, RT30, second batch. The same number is on the vial, the carton, the packing list and the certificate, and any of them can be checked on the certificate page. How a number is read and checked: batch numbers and how to verify one.

What arrives with the goods

A packing list with the batch number against each line. The certificate of analysis for each batch, sent with the shipment, and again on request: a peptide line’s certificate carries the chromatogram and the mass spectrum, and another line’s carries the results its own page lists. Reading one: how to read a peptide COA; what each of its HPLC and mass results is: HPLC and mass spectrometry on a certificate.

Endotoxin: which lines report it

Endotoxin is reported on the certificates of the lines made from a biological source rather than by synthesis, 11 of them, and each one’s specification lists it as reported on the batch certificate:

  • ACE-031, a recombinant fusion protein expressed in mammalian cells
  • Follistatin, a recombinant glycoprotein produced in mammalian or insect cells
  • GDF-8, a recombinant protein, expressed and refolded
  • IGF-1 LR3, a recombinant analogue expressed in E. coli and refolded
  • IGF-DES, a recombinant product refolded from E. coli
  • Cerebrolysin, a preparation made by enzymatic digestion of purified porcine brain protein
  • Thymalin, a peptide preparation extracted from bovine thymus
  • EPO, a recombinant glycoprotein expressed in mammalian cells
  • HCG, a glycoprotein hormone obtained from urine or made recombinantly
  • HMG, a preparation purified from urine
  • Insulin, made recombinantly

A peptide line is made by solid-phase synthesis, and its certificate reports purity, net content and identity; endotoxin, sterility and heavy metals are not in its specification.

Storage and retest

Lyophilised stock is held at minus 20 degrees Celsius away from light; solutions at 2 to 8 degrees; ancillaries at ambient. Shelf life is twenty-four months from manufacture. Every batch carries a retest date, and stock past it is pulled from sale automatically. Re-analysis against specification is recorded on the certificate, and the number of retest cycles is capped. More: storing lyophilised peptides and retest dates and shelf life.

If a batch is wrong

Send the desk the batch number and what you are seeing. We pull the retained sample, test it against the same specification, and send you the result. Out of specification: the batch is withdrawn, every account that received it is told, and your order is replaced or credited. In specification: you get the data and we say so. Every case and how to report it: claims, refunds and returns.

What these are

Research chemicals for laboratory use in vitro. Not for human or animal consumption, not for food, cosmetic or drug use, not manufactured under GMP, not for clinical use.

Questions about purity and testing

What purity are your research peptides?

Not less than 98.0 percent by RP-HPLC at 220 nm. That is the release limit, not a target: a batch whose certificate result falls below it is held back rather than sold at a discount. The specification also caps any single related substance at 1.0 percent; that line is not reported batch by batch, and the desk answers for a particular batch. The certificate for any batch prints the measured figure; the limit it is released against is the specification on the compound page. It is the limit for the peptide lines. The protein, glycoprotein and preparation lines are released on the methods their own pages name: size exclusion and SDS-PAGE for most, and RP-HPLC against the limit stated on the batch certificate for IGF-1 LR3, IGF-DES and Insulin; each product page prints its own specification in place of this one.

What does 98 percent purity actually mean?

It is an area percentage of the chromatogram, not a weight. A 10 mg vial released at 99 percent holds 10 mg of material by weight, and 99 percent of the detected peak area belongs to the peptide. So it says nothing about the water and the acetate counter-ion in that 10 mg; the specification bounds those separately, water at not more than 8.0 percent and acetate at not more than 15.0 percent. Peptide by weight is a separate figure called net peptide content. What 98 against 99 comes to in practice: what 98 or 99 percent purity means.

Is 99 percent better than 98 percent?

Only if you know what the other one percent is, which is why the specification bounds the individual impurities as well as the total. A batch at 99.2 percent with one related substance at 0.7 percent is not obviously better than one at 98.6 percent spread thinly. Read the purity and identity lines together, and ask the desk for the related-substance profile and the water result of that batch, not just the headline.

Who issues the certificate?

It is issued from the batch register the certificate page looks up, with the batch number and, for each result, the method and the result: for a peptide line, purity by RP-HPLC, net content and identity by mass spectrometry; a protein, solution or ancillary line reports the results its own page lists. We do not write certificates by hand, and we will not issue one in a buyer’s name. Any batch number can be checked against the register its certificate was issued from, on the certificate page.

What does the certificate for a batch report?

For a peptide line, three results: purity by RP-HPLC, net content against the label, and identity by mass spectrometry, with the chromatogram and the spectrum attached. The specification sets further limits for a lyophilised peptide (related substances, water, acetate and residual solvents); those are not reported on the certificate, and the desk answers for a particular batch on request. Both are set out on the certificate page. A solution line’s certificate reports appearance, identity and an assay for each labelled component, and its net content; a protein line’s reports purity and identity by the methods it names, endotoxin and net content; each page says which.

Is endotoxin on the certificate?

Not for a peptide line: endotoxin, sterility and heavy metals are not in a peptide line’s specification and are not on its certificate, which reports purity, net content and identity. The protein, glycoprotein and preparation lines report endotoxin on their certificates, as each one’s page lists: ACE-031, Follistatin, GDF-8, IGF-1 LR3, IGF-DES, Cerebrolysin, Thymalin, EPO, HCG, HMG and Insulin.

Why does a certificate carry both HPLC and mass spectrometry?

They answer two different questions. On a peptide line’s certificate the RP-HPLC result is purity, the share of the chromatogram’s peak area at 220 nm that belongs to the main peak, and the mass spectrometry result is identity, the measured mass against the one calculated from the formula. Neither stands in for the other: a purity figure does not say which molecule the main peak is, and a mass does not say how much else is in the vial. An epimer, the same chain with one residue’s configuration changed, has the same formula and the same mass; telling the two apart takes HPLC run beside a reference of the epimer, which the certificate does not carry. What each result is, and what telling two close lines apart takes: HPLC and mass spectrometry on a peptide certificate.

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