How to Check a Multi-Component Research Blend

Why a blend is a different analytical problem

A single research peptide has one sequence, one formula and one set of expected ions. A blend has several of each, and the properties that make a single compound easy to check, such as one main peak, one intact mass and one amount, are replaced by a list.

The record for a blend is correspondingly longer, and a general statement such as high purity says very little about whether every declared component is present at the declared level.

Two kinds of blend

The first kind is a peptide blend, in which every component is a defined peptide with its own formula and mass. Examples on the Vesta site are the GLOW and Klow blends and the BPC-157 plus TB-500 kits. Each component can be identified by LC-MS and has a reference page with expected values. The second kind is a mixed formulation, in which the ingredients are small molecules, enzymes or phospholipid mixtures.

The Lipo-C products and Lemon Bottle are of this kind. These need different detectors and assays, and some ingredients are mixtures themselves.

Identity: expected ions for every component

For a peptide blend, work out the expected ions for each component before looking at the data. In a blend of a tripeptide of 340.19 Da, a 15-residue peptide of 1418.70 Da and a 43-residue peptide of 4960.49 Da, the tripeptide appears mainly at m/z 341.19 ([M+H]+), the middle peptide at m/z 710.36 ([M+2H]2+) and the large peptide as a series at charge states from 3+ to 6+, for example m/z 993.10 for [M+5H]5+.

Each of these should be found at the retention time of its own chromatographic peak. Finding all three masses in one averaged spectrum, without separating the peaks, does not show which peak carries which mass.

• List each component with its formula and monoisotopic mass.
• Calculate [M+H]+ and the main multiply charged ions.
• Extract those masses from the LC-MS run and check that each belongs to its own peak.
• Check for near-isobaric neighbours: a pair of tripeptides that differ by 2.04 Da overlap in their isotope envelopes and need retention time to be told apart.

Purity: one peak, several peaks, and area percent

The chromatogram of a correct peptide blend has several main peaks, one for each peptide. A purity figure for the whole chromatogram has no clear meaning, because the largest peak may simply belong to the component present in the largest amount. A better record reports the purity of each component peak, or reports related-substance peaks for each.

Also remember that area percent depends on detector response, which differs between peptides, so the area ratio of two peaks is not their mass ratio.

Amount: declared, assayed and net

Component amounts are normally declared masses, for example 10 mg of a peptide per vial. These are not measurements of the batch. The peptide content of a declared mass is lower than the mass itself, because each powder holds counter-ions and water, as explained in the guide to counter-ions and net peptide content.

A component such as a copper peptide has an additional question: whether the declared mass refers to the peptide or to the copper complex. A complete record states the basis of each declared amount and whether any component was assayed.

Mixed formulations: choose the detector for the ingredient

UV detection near 220 nm works for peptides because the peptide bond absorbs there. It does not work for every ingredient. Inositol and choline have no useful UV absorbance, and methionine absorbs weakly, so a UV purity figure says little about them. Light-scattering and charged-aerosol detectors, refractive-index detection, mass spectrometry and NMR are used for such ingredients.

Vitamin B12 is the opposite case: cyanocobalamin absorbs strongly near 361 and 550 nm and is easily quantified by UV-visible spectroscopy. Ask which detector produced each value.

Ingredients that are mixtures

Enzymes such as bromelain are quantified by activity, with a defined substrate and unit, and not by milligrams of protein. Lecithin is a mixture of phospholipids, and its specification is the content of phosphatidylcholine, measured by HPLC with light-scattering detection or by 31P NMR. For both, the batch will differ slightly from the last, and the document to request is the specification with the assay method.

An enzyme that cleaves peptides should not be placed in a peptide solution in vitro unless digestion is the aim.

What to request and file

Ask for the formulation sheet with every ingredient, its grade and its declared amount; for each peptide, the intact-mass LC-MS result and the chromatogram with the peaks labelled; for each other ingredient, the assay method; and the batch code on every document.

File these with the vial photographs and the receiving record using the compound identity file template, and add a line for each component so that none is left without evidence.