Net and Gross PeptideWhat is the difference between gross peptide weight and net peptide weight?
Net peptide weight is the weight of the total peptide. Some products from the Peptide Institute are distributed in premeasured vials. These are indicated by the suffix –s or –v in the catalog. The net peptide weight is precisely determined by amino acid analysis after acid hydrolysis, HPLC, and/or UV absorption, and the value is indicated clearly on the vial label. The indicated weight is only for the net peptide molecule, and the weights of any constituents are excluded from the quantity. The amount of usable peptide meets and may exceed its advertised quantity.
Gross peptide weight is the weight of the peptide and peptide impurities as well as non-peptide components.
Peptides manufactured by vivitide are sold in gross peptide weight, however, we can offer net peptide vialing by request.What is net peptide content and what does it mean? If my peptide is 95% pure, what is in the other 5%?
The weight of dry peptide does not consist of peptide only, but includes non-peptide components such as water, absorbed solvents, counter ions and salts. Net peptide content is the actual percent weight of peptide. This number may vary, from 50 to 90 percent depending on the purity, sequence, and method of synthesis and purification. Do not confuse peptide content with purity; they are two distinctly separate things. Purity is usually determined by HPLC and defines the percent of the sample that is the target peptide sequence. Net peptide content only gives information on the percent of peptide versus non-peptide components. Net peptide content is accurately found by performing amino acid analysis or UV spectrophotometry. This information is important when calculating concentrations of peptide during sensitive experiments. If you need help, please ask us.
Peptide purity is determined by reverse-phase HPLC using a standard gradient established by vivitide (1% per minute). During synthesis, the coupling reaction of one amino acid to another is not always 100% efficient, causing a variety of deletion sequences to be generated. Most of the deletion sequences are purified out, but a few may have similar chromatographic characteristics to the target peptide. These remain in the peptide sample and account for the percent of impurities.
Can you explain the packaging of the Peptide Institute catalog products (bulk, -v, -s products)?
We carry the full line of quality products of the Peptide Institute of Osaka, Japan. Those that have a catalog number with a -v and -s suffix are packaged as net peptide and are in injection vials. The products without a suffix are "bulk" and packaged by gross weight.
Vialed (-v and -s) Products:
A peptide with constant weight is lyophilized and sealed under nitrogen in each vial. The net peptide weight is precisely determined by amino acid analysis after acid hydrolysis, HPLC analysis and/or UV absorption measurement, which is indicated clearly on the label of each vial. The indicated weight is only the net peptide molecule and does not include the weight of any additional constituents (water, acetic acid, and so on). For example, code 4002-v Bradykinin is described as follows:
PBK-4002-v Bradykinin (0.5 mg vial), M.W. 1060.2 g/mol
This indicates that each vial contains approximately 0.5 mg of bradykinin and the exact weight is indicated on the label (for example, 0.53 mg) and the instruction sheet (for example, 0.53 mg, 0.50 μmol). The weight is determined carefully and precisely by experts in our quality control department; therefore, we guarantee the quantity in each vial even if the content seems to be a small quantity.
A peptide solution of a known concentration can be constituted easily by injecting a given volume of a suitable solvent, indicated in the instruction sheet, into the vial using a calibrated syringe and dissolving the contents thoroughly. The peptide content in each vial is relatively small and accurately measured, therefore, the peptide should not be taken out of the vial to prepare a solution with a guaranteed concentration. The instruction sheet can be found on the last page of the ADS/COA.
The amorphous powder of each peptide is thoroughly dried over desiccant in vacuo and then weighed into a screw-capped bottle. Thus, the weight indicated on the label represents the gross weight of the amorphous powder, which includes the peptide as well as the accompanying water and acetic acid, if any. This is also called "gross" peptide. The amount of water and acetic acid in each amorphous powder is precisely determined by elemental analysis, Karl Fischer titration or gas chromatography. In some cases, peptides contain hydrochloride, trifluoroacetate, or ammonia instead of acetic acid. The observed value(s) of such accompanying constituent(s) is given in the structural formula of the respective peptide described in this catalog. For example, code 4002 Bradykinin is described as follows:
PBK-4002 Bradykinin (Bulk 100 mg)
M.W. 1060.2 • 120.10 • 54.05 g/mol
The total molecular weight of this amorphous powder is calculated to be 1234.4, which consists of 1060.2 for the net bradykinin molecule, 120.10 for two molecules of acetic acid and 54.05 for three molecules of water. This means that 100 mg of this powder contains net 85.9 mg of bradykinin molecules. Amounts of the accompanying water and acetic acid vary with the lot; the exact value in the purchased peptide is available on request. Given the hygroscopic nature of amorphous powder, precise weighing of a small quantity of peptide is not an easy task.