Peptide characterization: sequence confirmation, disulfide bonds, amino acid analysis, targeted quantitation and unknown identification
Purity by HPLC tells you how much of a sample is the main peak. It doesn’t tell you whether the main peak is the right molecule, whether the bridges in a cyclic peptide are in the right place, or what an unknown peak is. We use high-resolution Orbitrap LC-MS and triple quadrupole LC-MS/MS to answer those questions for peptides, proteins, supplements, cosmetics and pharmaceuticals.
Testing is quoted per sample or per project.
MS/MS fragmentation confirms the amino acid order, and catches substitutions, deletions, truncations and scrambled sequences that an intact mass can miss.
Molecular weight to within a few parts per million. See intact mass.
Digestion and LC-MS/MS of larger peptides and proteins such as GLP-1 analogs. See peptide mapping.
Confirms which cysteines are bridged in peptides such as oxytocin, octreotide and desmopressin, and finds mispaired or open bridges.
Amino acid composition after hydrolysis, for net peptide content, protein and amino acid label claims, and food protein. See the section below.
Measuring specific compounds at low levels in complex products, such as peptides in serums and creams or actives in supplement blends.
Identifying unknown peaks, impurities, degradants, adulterants and contaminants by accurate mass, isotope pattern and fragmentation.
Two peptides can have the same mass and a different sequence, and a peptide can have the right sequence with its disulfide bridges in the wrong place. Sequence confirmation fragments the peptide and reads the pieces back to the sequence. Disulfide analysis compares the peptide with its bridges intact and after they are broken, to show which cysteines are connected. These tests matter most for new or unusual peptides, products from a new supplier, and any material where the identity is in question. For routine purity and identity, see peptide testing.
Amino acid analysis breaks a peptide or protein down to its individual amino acids and measures each one. For peptides, it gives the net peptide content, which is how much of a vial’s weight is actually peptide rather than water, counterion and salts. For supplements, it confirms label claims for protein, collagen, BCAAs and individual amino acids. For foods, it gives a full amino acid profile. Acid hydrolysis destroys tryptophan and changes cysteine, methionine, asparagine and glutamine, so those need extra steps or are reported as noted.
Triple quadrupole LC-MS/MS in multiple reaction monitoring mode measures specific compounds with high selectivity, even when they are a tiny part of a complicated product. Typical uses are cosmetic peptides such as copper peptides and acetyl hexapeptide-8 in creams and serums, peptides in finished supplements, and low-level actives or contaminants in blends.
When a new peak shows up in a chromatogram, or a product smells, looks or tests wrong, high-resolution LC-MS gives the exact mass and isotope pattern of the unknown, and MS/MS breaks it into pieces that show its structure. Results are compared against spectral libraries and confirmed with a reference standard when one is available. The report says how confident each identification is. This is used for impurities and degradants, complaint and recall samples, adulterants, and anything that doesn’t match its specification.
Tell us the sample and the question you need answered.
We confirm the approach, the sample amount and any reference material needed.
Results with the data behind them, and a plain explanation of what they mean.
Not always. Peptides with the same amino acids in a different order have the same mass. Sequence confirmation by MS/MS shows the order.
The percentage of a sample’s weight that is actually peptide. The rest is water, counterions such as TFA or acetate, and salts. Amino acid analysis is one way to measure it.
Yes. Targeted LC-MS/MS can measure cosmetic peptides in finished products. The method may need to be set up for your formula first.
We need the sample, not just the chromatogram. With the sample, we can usually give the unknown’s exact mass, formula and a likely structure.
Usually a few milligrams for peptide work. We confirm the amount with your quote.
Tell us about your sample and what you need to know, and we’ll send back a quote. You can also email [email protected].
