A Selank certificate of analysis is a test report for one lot. Read it in order: the lot number against the vial, then the test date. Next is identity by mass spectrometry near 751.9, then purity by RP-HPLC with the chromatogram attached. Last come net peptide content, counterion, water, and the lab that issued it.
- Selank is C33H57N11O9, average mass near 751.9, PubChem CID 11765600.
- No sulfur in the formula means no methionine and no cysteine, so no oxidation or disulfide route.
- Proline residues cause cis-trans conformational isomers that broaden or split the peak.
- Conformational isomers weigh the same; a mass detector distinguishes them from impurities.
- No aromatic residues means essentially no absorbance at 280 nm, so 214 is the wavelength.
- Lysine and arginine make retention dependent on the ion-pairing additive used.
What does a Selank certificate actually certify?
Picture a receipt from a lab: what was measured, on which lot, on which day. It is a record of one sample, not a promise about every vial.
It records what a named laboratory measured on a sample drawn from one lot, on one date, by named methods. It is evidence about that sample rather than a warranty about the vial on your bench.
Two documents get confused constantly. A specification sheet lists limits the product is supposed to meet, carries no lot number and no results, and describes an intention. A certificate carries both because it describes an event.
If the page in front of you has no lot number on its face, it is the first kind of document whatever the heading claims.
- Lot number on the report against the lot number on the vial
- Test date after the fill date, and distinct from the print date
- Identity: observed mass against an average near 751.9
- Peak shape: proline isomers broaden or split the peak without being impurities
- Purity at 214 nm, because the molecule has no chromophore at 280
- Net peptide content, counterion and water by Karl Fischer
- Accession number confirmed at the issuing laboratory
How do you read it field by field?
Lot number first, against the vial, and nothing further until they match. Then dates: the test date should follow the fill date, and a print date carries no analytical meaning.
Then the results in order of weight. Identity by mass spectrometry. Purity by reversed-phase HPLC with the chromatogram attached rather than summarised. Net peptide content. Counterion. Water. Appearance last, because it tells you least.
Every result needs a method beside it. Purity by area percent, by net peptide content and by amino acid analysis are three different numbers for one vial and they do not agree with each other. A figure with no method attached cannot be reproduced by anyone.
What mass should the identity result show?
Selank is a heptapeptide, the tuftsin fragment extended with a Pro-Gly-Pro tail. Its molecular formula is C33H57N11O9 with an average mass near 751.9, cataloged as PubChem CID 11765600.
Look at what that formula does not contain. There is no sulfur, so there is no methionine and no cysteine, which removes the oxidation route that dominates several other peptides in this catalog and removes disulfide chemistry entirely.
That makes Selank chemically simpler than most of its neighbours. Its analytical difficulty lies somewhere else, in the shape of the chromatographic peak rather than in the mass.
Why can the main peak look broad or doubled?
Because of the prolines. Selank carries several, and proline is the one residue whose preceding peptide bond interconverts between two forms, usually described as cis and trans.
Both forms are the same molecule. They weigh the same and they are chemically identical. But they can have slightly different shapes, and reversed-phase separation responds to shape, so the two can travel through the column at marginally different speeds.
The result on a chromatogram is a peak that is broader than expected, or in some conditions a peak that appears split into two. It is easy to read that as an impurity, and for a proline-rich peptide it very often is not.
How do you tell peak splitting from a real impurity?
By whether the two components weigh the same. Conformational isomers of one molecule have identical mass; a genuine impurity almost never does. A mass detector on the same run settles it immediately.
Temperature is the other diagnostic. Interconversion between the two forms speeds up as the column warms, so raising the column temperature tends to merge a conformational doublet into one peak. A real impurity does not obligingly disappear when the column gets warmer.
A certificate that reports a purity figure without the chromatogram gives you no way to know which you are looking at. For this compound that omission costs more than it does for most.
Does the basic side chain affect the separation?
Yes. Selank carries lysine and arginine, both strongly basic, and basic peptides interact with residual acidic sites on silica-based columns. That interaction causes tailing and unpredictable retention.
The standard remedy is an ion-pairing additive in the mobile phase, most often trifluoroacetic acid, which pairs with the positive charges and restores a clean peak shape.
The practical consequence for a reader is that retention time for this peptide depends heavily on mobile phase composition. Two laboratories with different additives will report different retention times for identical material, which is one more reason retention time alone is weak identity evidence.
What does the purity figure leave out?
Anything that does not absorb at the detection wavelength or does not elute. Purity is an area percentage of what the detector saw.
Detection matters more than usual here. Selank contains no tryptophan, tyrosine or phenylalanine, so it has essentially no absorbance at 280 nanometres. A laboratory reading this peptide at 280 would see almost nothing, and the only sensible wavelength is 214, which responds to the peptide bond itself.
That is a useful cross-check on a certificate. A purity figure for Selank reported at 280 nanometres is a figure to ask about, because the molecule has no meaningful chromophore for it.
What is net peptide content, and why does it change the price?
A synthetic peptide is not shipped as pure peptide. It carries a counterion from purification, usually trifluoroacetate or acetate, and it carries water because lyophilized peptide is hygroscopic.
The consequence is arithmetic. A vial labeled 10 milligrams may hold 10 milligrams of powder of which a real fraction is salt and water. Net peptide content of 80 percent means 8 milligrams of peptide, and two suppliers quoting the same price for the same nominal size are not selling the same amount.
Ask which basis the label uses. The cost per milligram comparison ranks the catalog on one basis for exactly this reason.
What do the water and counterion fields tell you?
Water is measured by Karl Fischer titration, which is specific to water. Loss on drying reports everything volatile and reads high when residual solvent is present, so the two are not interchangeable.
Counterion identity is worth reading. Trifluoroacetate is the usual residue of preparative HPLC and is not inert in every experimental context; acetate is produced by an extra exchange step. For a basic peptide like this one the counterion is present in greater proportion than for a neutral peptide, because there are more positive charges to balance.
Both figures feed the net content arithmetic and together explain most of the gap between area purity and net peptide content.
What does the certificate not cover?
Everything after the sample was drawn. Storage temperature, light, how long the vial has been open and how many times it has been entered are all outside it.
Lyophilized peptide is hygroscopic, so a vial opened in a humid room takes on water that changes the net content arithmetic without changing anything visible. The number was true when measured and is now slightly generous.
Handling belongs with the storage record rather than the test report. Reading a certificate as though it covered both is the common mistake, and it is why a recent certificate on a badly stored vial proves very little.
How do you verify the document is genuine?
Confirm the report at the issuing laboratory rather than with the seller. An independent laboratory issues each certificate against an accession number or verification key that resolves on its own site. If that number resolves to a different product, a different lot, or nothing, the document does not describe your material.
Certificates with the verification key removed deserve particular suspicion, and this is not a hypothetical concern in this market. A PDF is easy to edit; a third-party lookup is not.
Lot reports for material supplied here resolve through the certificate verification page, and the sizes carried appear on the Selank product record.
What is the regulatory position?
There is no FDA-approved drug product containing Selank and no United States pharmacopeial monograph defining what an acceptable batch is. That absence is worth stating plainly: the specification a lot is released against is the supplier's own.
What a research certificate can honestly establish is narrower and still useful: what a named laboratory measured, on a named lot, on a named date, by named methods. Read against that standard a good certificate is strong evidence and a vague one is none.
Material described here is supplied for laboratory use only, and nothing in this guide describes use in a person or an animal.
FOR LABORATORY AND IN-VITRO RESEARCH USE ONLY. NOT FOR HUMAN OR ANIMAL CONSUMPTION. NOT FOR PERSONAL, MEDICAL, DIAGNOSTIC, THERAPEUTIC, OR RECREATIONAL USE.
What is Selank studied for?
Published research on Selank investigates the areas below, which is a different question from what Selank will do for anyone, a claim about a living system that nothing on this site is sold for.
What it is. A man-made peptide seven building blocks long, based on an immune peptide called tuftsin.
What the research looks at. It appears in animal work coming largely from a narrow set of research groups, which is worth carrying in mind while reading it.
How it is thought to work. Built from tuftsin with a short tail added for durability. How it works is not settled in the published research.
What is not established. No approved product in the United States and no official standard. The evidence base is smaller and more geographically concentrated than commercial writing implies.
The full record, including the certificate for the lot in stock, is on the Selank product page.
Common questions
What molecular mass should a Selank certificate show?
Why does the Selank peak look broad or split?
How do you tell peak splitting from a real impurity?
Can Selank purity be measured at 280 nanometres?
Why does a basic peptide need an ion-pairing additive?
Published certificates for Selank
Every figure below is read from a report the laboratory issued for that lot; each page carries the PDF and the lab's own verification link.
More documentation guides
Sources
- PubChem Compound Summary for CID 11765600, Selank. The openable record for Selank, giving the molecular formula C33H57N11O9 and the average mass near 751.9 that an identity result is read against, and showing the absence of sulfur and aromatic residues discussed above.
- ICH Q2(R2), Validation of Analytical Procedures . Defines specificity, accuracy and precision for identity and assay procedures, and is the basis for requiring that each certificate result names the method that produced it.
- FDA guidance, Q6B Specifications: Test Procedures and Acceptance Criteria. Sets out how identity, purity and content are constructed as separate attributes, and why a purity figure is reported with the method and conditions that produced it.
- Finnrick independent verification portal. Third-party lookup used to confirm a certificate resolves to the lot it claims to describe, rather than confirming a document with the seller who supplied it.
