Fields that identify the document
Before any result means anything, the certificate has to say which material it describes, who tested it and when.
- Certificate of Analysis (COA)
- The analytical record for one batch of material: what was tested, by which method, on which date, and what the instrument reported. It describes that batch and no other. Our guide to reading a COA field by field walks through a full example.
- Batch reference (lot number)
- The code that ties a certificate to the material produced in one run. Batch and lot are used interchangeably. It is the first field to check, because the code on the vial has to match the code on the certificate or the results describe something else. See batch numbers and traceability, and record the match on arrival with the receiving record.
- Test date
- The date the analysis was run. It says when the measurement was true, not how long it stays true. Compare it with the production date and the date you receive the material: a long gap is a question to ask, not a verdict. See check the date, then check the gap.
- Issuing laboratory
- The organisation that ran the analysis, named with an address or other contact details you can check independently. A certificate with no identifiable laboratory cannot be confirmed by anyone other than the party who sent it.
- Third-party testing
- Analysis by a laboratory with no commercial stake in the result. In-house testing is still useful; it answers a different question. What independence requires, and how to read an external report, is covered in third-party versus in-house testing.
- Specification and result
- A specification is the limit a batch had to meet. A result is what was actually measured. A certificate that prints only the specification, or only "pass", tells you the target and not the measurement, so ask for the measured value.
- Nominal fill weight
- The quantity printed on the label, such as 10 mg. It is the target mass of dried powder in the vial, not the mass of peptide, because the powder also holds counterion and residual water. See nominal fill weight is not peptide mass.
Purity by HPLC
The purity line on a peptide certificate almost always comes from liquid chromatography. These are the terms on and around the trace.
- HPLC
- High performance liquid chromatography. A dissolved sample is pushed through a packed column under pressure, and different molecules leave the column at different times. A detector records what comes out. See what HPLC actually measures.
- Reverse-phase HPLC (RP-HPLC)
- The form of HPLC used for most peptides. The column packing is water-repellent, and molecules are separated by how strongly they cling to it as the solvent mix changes. It is also the usual purification step, which is why trifluoroacetate often stays with the finished material as its counterion.
- Chromatogram
- The trace the detector produces: signal on the vertical axis, time on the horizontal. The purity figure is a summary calculated from it. The trace itself shows what the summary leaves out, which is why it is worth asking for. See reading a chromatogram.
- Main peak
- The largest peak on the chromatogram, taken to be the target compound. Its share of the total peak area is the reported purity. Look at its shape as well as its size: a clean, symmetrical peak and a quiet baseline either side say more than the number.
- Retention time
- How long after injection a compound leaves the column, usually in minutes. It depends on the column, the solvents and the gradient, so a retention time only means something within one method. On a two-component material, two compounds with similar retention times can overlap and neither purity figure is reliable; see chromatographic resolution.
- Area percent
- How HPLC purity is calculated. Software measures the area under every detected peak and reports the main peak as a percentage of the total. It is a share of what the detector saw, which is not the same as a share of what is in the vial.
- Detection wavelength
- The ultraviolet wavelength the detector reads at. Peptide bonds absorb in the low UV, so peptide methods typically read around 210 to 220 nm. A different class of molecule may be read elsewhere; see why the detection wavelength differs for NAD+. A purity figure with no wavelength stated is harder to interpret.
- Shoulder
- A bump on the side of the main peak. It usually means a closely related impurity is partly hidden under the target, which inflates the reported purity. Shoulders are more common on long sequences, where deletion products elute close to the full-length peptide.
Identity by mass spectrometry
Purity says how much of the detected material is one thing. Identity says whether that thing is the compound named on the label.
- Mass spectrometry (MS)
- A method that turns molecules into ions and measures them by mass. Because a peptide's mass is fixed by its sequence, the expected value can be calculated in advance and compared with what the instrument reads. See why identity needs mass spectrometry.
- LC-MS
- Liquid chromatography coupled to a mass spectrometer, so each peak can be given a mass as it leaves the column. It connects the purity trace and the identity result in one run, which a separate HPLC and MS report cannot do.
- Expected mass
- The theoretical mass calculated from the molecular formula. On a modified peptide it has to account for the whole molecule, not only the amino acid backbone. The expected value should be printed next to the observed one.
- Observed mass
- The mass the instrument actually measured. Identity is confirmed when it agrees with the expected mass within the method's tolerance. A certificate that says "identity confirmed" with no numbers gives the reader nothing to check. See reading the identity result.
- Mass-to-charge ratio (m/z)
- What a mass spectrometer measures directly: the mass of an ion divided by its charge. A singly charged ion reads close to the molecule's mass. A larger peptide often carries several charges, so its signals appear at a fraction of the full mass.
- Charge state
- How many charges an ion carries, written as [M+H]+, [M+2H]2+, [M+3H]3+ and so on, where M is the molecule. A report showing a series of charge states is normal for a peptide. The molecular mass is worked back from them, and the report should say which ion it used.
- Monoisotopic and average mass
- Two ways to state a molecular mass. Monoisotopic mass uses the most abundant isotope of each element. Average mass weights every isotope by its natural abundance and comes out higher. The two differ by more as the molecule gets larger, so the certificate should say which one it compared.
What else is in the vial
A vial of dried peptide is not pure peptide by weight. These terms explain the difference, and why it does not contradict a high purity figure.
- Net peptide content
- The share of the powder's total weight that is peptide, after counterion and water are accounted for. It is a separate determination from purity, with a different denominator, and the two figures do not need to agree. See purity and peptide content answer different questions.
- Counterion
- The ion paired with a charged peptide to form a salt. Trifluoroacetate (TFA) is the usual one, carried over from reverse-phase purification. Acetate is another. The counterion adds weight to the powder, so it lowers net peptide content without affecting HPLC purity.
- Salt form and free base
- Reference databases often list a peptide's formula and weight for the free base, with no counterion. The material in a vial is usually a salt, which weighs more. Our product pages state which form a figure refers to, as on the BPC-157 + TB-500 listing.
- Water content (Karl Fischer)
- Residual moisture in the dried material, usually measured by Karl Fischer titration, which is a different method from the one used for purity. It matters most on materials that absorb moisture from the air; see water content on an NAD+ certificate.
- Lyophilised (lyophilized)
- Freeze-dried: frozen, then dried under vacuum so the water leaves as vapour. A well-formed cake shows a competent drying cycle. It is not evidence of purity, identity or fill weight. See what lyophilised peptides are.
Whether the document is genuine
A real certificate can still belong to a different batch, and a convincing one can be edited. These terms cover both checks.
- Original file
- The PDF as the laboratory issued it, rather than a screenshot or a photo. An original carries metadata and text that can be searched and compared. An image carries neither, so it is easier to alter and harder to check. See verifying the document.
- Report verification
- Confirming with the issuing laboratory that a report is one it produced, using contact details you found yourself rather than those printed on the document. It establishes that the certificate is real. It does not establish that the certificate describes your vial; the batch reference does that.
- Representative COA
- A certificate for an earlier or different batch, offered as typical of the product. It shows the supplier has tested something at some point. It says nothing about the batch you would receive, so ask for the certificate carrying that batch's reference.
Put the terms to work
The COA checker scores a certificate against the fields above. Our quality page explains how we report purity per batch rather than per product, and every item in the catalogue links to its documentation.
Request the certificate for a batchFrequently asked questions
What does HPLC mean on a certificate of analysis?
High performance liquid chromatography, the method behind most purity figures on a peptide certificate. The sample is separated in a column and a UV detector records each component as it leaves. Purity is reported as the main peak's share of the total peak area, so it is a share of what the detector saw, not of everything in the vial.
What is the difference between peptide purity and net peptide content?
They have different denominators. HPLC purity is the share of detected peptide-related material that is the target sequence. Net peptide content is the share of the powder's total weight that is peptide, after counterion and residual water. A material can show a very high purity and a noticeably lower peptide content, and the two figures do not contradict each other.
What does m/z mean on a mass spec report?
Mass-to-charge ratio: the mass of an ion divided by its charge, which is what a mass spectrometer measures. A larger peptide usually carries several charges, so it appears as a series of signals at fractions of its full mass. The molecular mass is calculated back from those, and the report should show the observed value next to the expected one.
What is a lot number on a COA?
The same thing as a batch number: the code that ties the certificate to material made in one production run. It should match the code printed on the vial exactly. If the two differ, the certificate may be genuine and still describe a different batch, so ask the supplier for the one that carries the reference on your vial.