FAQ - Peptide Specification

Peptide Specification

The following items cover our most FAQ´s and explain some important terms in the field of peptide research:


Certificate of Analysis

Each peptide is supplied with a lot-specific certificate of analysis, which usually contains the following information: sequence, molecular weight (measured by mass spectrometry), and peptide purity (measured by HPLC profile). Additional analyses (e.g. optical purity, amino acid composition, moisture, residual solvent, peptide content, etc.) can be performed upon request with additional charges. We guarantee that the structure and the purity of our peptides meet the specifications stated in the certificate.


Counter Ion

Because of the low concentration of peptides used in most biological assay systems, possible effects of the counter ion can usually be disregarded. Unless otherwise specified by the client, due to the basic residues, our peptides are delivered as a TFA salt. Peptides can also be supplied as acetate salts, but are usually more expensive in this form given the need of additional work-up. The nature of the counter ion can seriously affect the solubility of the peptide.


Identity - for catalogue or GMP products only

The identity of our peptides is checked by co-chromatography based on our internal house standards, which have already been proven by extensive analysis.


Peptide Content

Most peptides contain basic and acidic side groups implying the presence of counter ions (trifluoroacetate salts). Because very few peptides crystallize, the normal method of preparation involves a final freeze drying step. Thus, in addition to the peptide and the counter ion, the lyophilisate may contain up to 5% residual moisture. Before reconstituting the peptide, ensure that the actual net peptide content given in the certificate of analysis is taken into consideration. The peptide content for most peptides usually lies in the range of 75 - 85%, but can be as low as 50 - 60% in peptides with a considerable excess of basic amino acid residues. Therefore, you must distinguish between the gross weight of the lyophilisate and the peptide net content. Peptides for research purpose are typically delivered as a gross weight lyophilisate, whereas GMP or catalogue peptides are delivered as net weight peptides. This information is clearly stated in the certificate (weight units).



It is very important to observe that "peptide purity" is not a synonym of "peptide content". Whereas peptide content provides information about the relationship between the peptide and the other components of the lyophilisate, peptide purity refers to the relative purity of the main peptide product to the other peptide impurities (when detectable). Peptide purity is calculated as the area percentage of UV-positive (210 - 220 nm) material eluted under the main peak of the HPLC chromatogram. Our catalogue peptides are intended for use in biological assay systems and are manufactured to attain a 97% or higher HPLC peptide purity. Because 97% is our lower limit of acceptability, most of our peptides exceed this purity grade. This can be observed in the HPLC profile provided with the certificate of analysis. In very few cases, the nature of the amino acids or the tertiary structure of the peptide prevents this purity level of being attained at a commercially acceptable price. In such cases, this information will be clearly stated in the certificate of analysis.