How to compare research peptide prices: per-milligram cost, net peptide content, and what a low price can hide

Start with the unit: price per milligram#

The first conversion is the obvious one. A 10 mg vial at $60 costs $6.00 per milligram; a 5 mg vial at $40 costs $8.00. Listings rarely state this, and a larger vial at a higher sticker price is often the cheaper material. Do the division before anything else, and do it per component for blends.

That is the easy part. The next three adjustments are where most comparisons go wrong.

Adjustment 1: gross mass versus net peptide content#

The number on a label is, at best, the mass of peptide material placed in the vial. Peptide material is not pure peptide. Synthetic peptides retain water and counter-ions from purification, and the fraction of the gross mass that is actually peptide, the net peptide content, is commonly 70–90% and sometimes lower.^[1] A 10 mg vial at 75% net content holds 7.5 mg of peptide; at 90% it holds 9 mg. Two listings at the same gross price therefore differ by 20% in real cost if their net contents differ by that much.

Net peptide content is measured by amino acid analysis or by quantitative methods against a reference standard, and it is distinct from HPLC purity. Purity says what fraction of the peptide material is the intended sequence; net content says what fraction of the total mass is peptide at all. A vial can be 99% pure and 70% net content. Our explainer on purity versus net peptide content covers the distinction; for pricing, the point is that a report which gives only purity leaves the real milligrams unknown.

Adjustment 2: the salt form#

Peptides purified by reversed-phase HPLC are usually isolated as trifluoroacetate (TFA) salts, because TFA is the standard mobile-phase additive. Each basic residue (lysine, arginine, histidine, the N-terminus) carries a counter-ion, and TFA, at 114 daltons per ion, adds appreciable mass: for a short, basic peptide the TFA can account for a tenth or more of the gross weight.^[2] Acetate is lighter (59 daltons per ion) and chloride lighter still. Converting TFA to acetate or hydrochloride costs the supplier an extra processing step, which is one reason acetate-form vials are priced higher at the same label mass.

There is a second reason the form matters beyond mass. Residual TFA is not inert in biological systems: Cornish and colleagues reported that TFA carried over from peptide purification affected cell proliferation in culture at the concentrations typically present, a finding that led many laboratories to specify the counter-ion for cell work.^[3] For pricing, the rule is simply that a label mass refers to the salt unless the listing says otherwise, and salts of different ions contain different amounts of peptide.

Adjustment 3: what testing is included#

A lot-specific Certificate of Analysis from a named laboratory costs the supplier real money per lot, and that cost is in the price. A listing without one is cheaper partly because the buyer is being asked to take on the testing, or the risk of not testing, themselves. Independent peptide testing services charge per sample, and the cost of testing a single vial from an untested lot often exceeds the price difference between a tested and an untested listing. When comparing, either add the cost of your own test to the untested vial or regard the two as different products.

A COA also changes what the label mass means. Some reports state the measured quantity of peptide in the vial rather than the nominal fill; where that is available, use the measured figure in the per-milligram calculation and the uncertainty about net content disappears.

Where a low price usually comes from#

None of the following is necessarily improper, but each is a reason a vial can be priced below the market and each is something to check rather than assume:

• Lower net peptide content. The commonest explanation. Cheaper synthesis and less thorough purification leave more water and counter-ion in the material.
• Lower purity. Crude or partially purified material is far cheaper to produce. A purity figure below about 95% is a meaningful difference in what is in the vial.
• No lot testing. The supplier has not paid for analysis, and may be relying on an upstream manufacturer's certificate that describes a bulk batch rather than the finished vial.
• Nominal rather than measured fill. The label states the intended mass; the fill was not weighed or assayed.
• Short-dated or re-labelled stock. Material that has been stored a long time, or stored badly, may no longer match any report; see our note on peptide storage and stability.
• Genuine scale. Large suppliers buy synthesis in larger batches and pay less per milligram. This is the benign case, and it is distinguishable from the others by the presence of lot-level documentation.

A five-line comparison#

1. Price ÷ label milligrams = gross cost per mg.
2. Multiply label mg by net peptide content (reported, or an assumed 80% if the listing is silent and the form is TFA).
3. Price ÷ net mg = real cost per mg of peptide.
4. Add the cost of an independent test if the lot has no COA from a named laboratory.
5. Compare the resulting figures, and keep the untestable listings in a separate column.

Renuvia's listings state the label mass and form on each product page, and each lot's report, including net content where the laboratory reports it, is published in the COA library when issued; pricing tiers for 2, 3 and 5 vials are shown on the product pages and larger quantities are handled through the wholesale program.