A purity of 99 per cent on a certificate of analysis describes proportions in a chromatogram, not how much peptide is in the powder. Those are two different numbers, measured by two different methods. Below is what each item on such a document means, what you cannot read from it, and how our shop lets you check where a vial comes from.
How we know what the document should look like
The point of reference is a consensus published in Clinical Chemistry in 2016. It was signed by several dozen authors from clinical laboratories, from peptide manufacturers to metrology institutes. The document describes how peptides should be characterised, stored and labelled so that results from different laboratories can be compared.
It was written for protein research, not for shops. That is exactly why it is a good reference: nobody wrote it to sell anything.
Chromatographic purity: what it really measures
The consensus points to reversed-phase high performance liquid chromatography on a C18 column with ultraviolet detection. The sample is separated into its components and the detector draws peaks. Purity given as a percentage is the share of the main peak in the area of all peaks.
This definition carries a limitation that sellers rarely mention. The method compares components with each other, so it does not see what the detector cannot see. Salt, water and counterions give no peak in ultraviolet and do not appear in this number.
Mass spectrometry: is it really the right molecule
The second method is mass spectrometry with electrospray ionisation or MALDI. The consensus calls it essential for confirming that the vial contains the intended product and for detecting impurities of a different mass. LC-MS/MS goes further and confirms the amino acid sequence together with the site of any modification.
The division of roles between the two methods is simple. Chromatography tells you how pure the sample is, mass spectrometry tells you whether it is the right substance. A certificate without the second leaves the identity of the contents an open question.
Peptide content: the number usually missing
The third item is called peptide content and describes how much actual peptide there is in the weighed sample. It excludes the mass of water and counterions, which are present in every peptide. It is determined by amino acid analysis, a different method from purity.
The practical consequence applies to every vial of lyophilised powder. A label saying 10 mg describes the weighed mass of powder, which also contains water and counterions. When you calculate concentration after dissolving, you work from the mass on the label, not the mass of pure peptide. The calculation itself is covered in the guide to reconstitution with bacteriostatic water.
Crude peptide versus purified peptide
The consensus splits products into two groups. Purified peptides go through chromatographic separation after synthesis, which removes most salts and synthesis reagents. Crude peptides do not have to go through that step, and then neither the exact amount nor the purity can be stated.
This is the heart of the difference between a vial with documentation and one without. A missing certificate does not prove the product is bad, but it leaves the buyer without a single number to check. How to recognise an original vial is explained in the guide to spotting genuine peptides.
Storage in the same document
The consensus also gives the conditions under which a peptide keeps its properties. For long-term storage peptides are lyophilised and kept at minus 20 to minus 80 degrees Celsius. Repeated freezing and thawing should be avoided, and working solutions are treated as short-term stock, for up to three months.
These conditions describe a laboratory, not a kitchen fridge. What carries over to a vial bought for your own research is covered in the guide to storing powder and solution.
How to check a vial bought from us
Bio-Peptide and Genheal place a unique code under the hologram. You scratch off the hologram, go to the manufacturer's website, open the authenticity tab and enter the code. Nouveaux Ltd. runs its own verification page. The steps are shown on the check your product page, and the differences between the brands themselves are covered in the guide to Bio-Peptide, Genheal and Nouveaux Ltd.
Verifying the code confirms where the packaging comes from, not what is inside. Those are two different questions and it is worth keeping them apart. The full list of items with prices is on the price list.
Frequently asked questions
What does 99 per cent purity on a certificate mean?
The share of the main peak in the area of all peaks in the chromatogram. Salt and water are not included in this number.
How does purity differ from peptide content?
Purity compares the components of the sample with each other. Peptide content tells you how much peptide there is in the weighed mass of powder.
Why is mass spectrometry on a certificate?
It confirms the identity of the molecule and detects impurities of a different mass. Chromatography alone does not settle that.
Is 10 mg on the label 10 mg of pure peptide?
No. It is the weighed mass of powder, which also contains water and counterions.
How do I check that a vial is original?
With the code under the hologram, on the manufacturer's website. Bio-Peptide and Genheal use a code, Nouveaux Ltd. runs its own verification page.
Sources
- Hoofnagle AN, Whiteaker JR, Carr SA et al. Recommendations for the Generation, Quantification, Storage, and Handling of Peptides Used for Mass Spectrometry-Based Assays. Clinical Chemistry, 2016, 62(1): 48-69. https://doi.org/10.1373/clinchem.2015.250563