Methods and terms
What HPLC, mass spectrometry, certificate of analysis, lyophilization and the other terms on our listings mean.
- HPLC
- High-performance liquid chromatography separates a sample on a column and reports how much of it elutes as the main peak; the purity figure on each listing is the area of that peak.
- Mass spectrometry
- Mass spectrometry measures the mass-to-charge ratio of the ionized compound and confirms that the molecular weight matches the expected sequence: an identity check, not a purity figure.
- Certificate of analysis (CoA)
- The lot-specific document that records the tests run on a batch, the methods, the results and the date. It is issued per lot, so it changes when the lot changes.
- Lot number
- The identifier printed on the vial and repeated on the certificate; it ties a physical vial to one production batch and one set of test results.
- Lyophilized
- Freeze-dried: water is removed from a frozen solution under vacuum, leaving a dry cake that stores longer than a solution and is reconstituted in the laboratory.
- Reconstitution solvent
- The sterile liquid used in the laboratory to dissolve a lyophilized sample to a known concentration for in-vitro work, for example bacteriostatic water.
- Purity
- The share of the sample that is the named compound, expressed as a percentage from the HPLC main peak; the remainder is related impurities, salts and water.
- Net peptide content
- The mass of peptide in the vial after subtracting counter-ions and water; the quantity stated on a listing is net peptide unless it says otherwise.
- Cold chain
- Keeping a temperature-sensitive reagent within its storage range from packing to the receiving freezer: insulated mailer, desiccant, tracked transit, no weekend holds.
- Desiccant
- A moisture-absorbing sachet packed with the vial so humidity does not reach a lyophilized cake during transit.
- Butyl stopper
- The inert rubber closure under the crimp cap; butyl rubber resists gas and moisture transfer and is the standard closure for lyophilized vials.
- Crimp seal
- The aluminium cap crimped over the stopper to keep the vial sealed until it is opened in the laboratory; a flip-off centre exposes the stopper.
- Borosilicate glass
- The low-expansion glass used for laboratory vials; it tolerates freezing and sterilization without cracking and does not leach into the sample.