Comparing Research Peptide Prices: What Cost per Milligram Hides

Price comparison in this market looks straightforward and is not. Two suppliers listing a 10 mg vial of the same compound at different prices appear to be offering the same thing at two prices. They are frequently offering different amounts of peptide, tested to different standards, delivered under different conditions, and the listed price is the least informative number in the comparison.

This note sets out what to normalise before comparing.

The vial is not the peptide

A lyophilised peptide is not supplied as a free base. It comes out of purification as a salt — most commonly a trifluoroacetate salt from reverse-phase chromatography — and it carries residual water, because lyophilised peptides are hygroscopic and a small amount of bound water survives drying.

So the mass in the vial is peptide plus counter-ion plus water. The fraction that is actually peptide is the net peptide content, and for a typical research peptide it lands somewhere in the region of 70–90% of the vial mass depending on the sequence, the salt form and how the material was dried. A 10 mg vial at 80% net content holds 8 mg of peptide; the same vial at 90% holds 9 mg. That is a 12% difference in what you actually receive, before price enters the picture.

The comparison you want is therefore price divided by milligrams of peptide, not price divided by nominal vial mass. Where a supplier does not publish net content, that division cannot be performed, and the honest conclusion is that the comparison is unavailable rather than that the cheaper listing wins. Our note on net peptide content works through the arithmetic, and counter-ions and salt form covers where the missing mass goes.

Purity multiplies the same error

Net content and purity are different quantities and both scale the amount of target compound you have. Net content asks how much of the vial mass is peptide at all. Purity asks how much of that peptide is the intended sequence rather than a deletion, truncation or oxidation product.

They compound. A 10 mg vial at 80% net content and 95% purity contains about 7.6 mg of target compound. The same vial at 90% and 99% contains about 8.9 mg — roughly 17% more, from two numbers that both looked like rounding differences in isolation.

A listing quoting neither figure is quoting a price for an unknown quantity.

Testing is part of the price

Independent analysis costs money per lot, and a supplier paying for it has that cost in their price. A supplier not paying for it does not, and the difference shows up as a lower listing.

What you are buying with that difference is the ability to know what you received. An untested lot is not cheaper material; it is material whose identity and purity are assertions. If the work it supports has to be defensible — to a supervisor, an institution, a reviewer or an auditor — the analysis is not optional, and buying it separately after the fact costs considerably more than a supplier amortising it across a lot. See third-party vs in-house testing.

Landed cost, not listed cost

An international listing and a domestic listing are not comparable at face value. Put the following on both sides:

• Currency conversion at the rate you will be charged, not the spot rate
• Shipping, including any cold-pack or express surcharge
• Duty and federal tax assessed on import by the CBSA, with the provincial component where it applies — against which a domestic order carries only the GST or HST of the delivery province, with no duty and no brokerage
• Carrier brokerage, charged on delivery, and routinely the largest unbudgeted line
• The cost of a hold: what a two-week clearance delay does to scheduled work

Brokerage and duty alone frequently close most of an apparent unit-price gap. Our comparison of importing versus sourcing domestically goes through the border step in detail.

Blends need the split, not the total

A blend priced against a single-compound vial is a category error unless the composition is stated. A 20 mg blend containing 10 mg each of two peptides is two 10 mg quantities in one vial; a 10 mg blend containing 5 mg of each is two 5 mg quantities. Without the split, the per-milligram figure for either component is unknown, and a blend can look inexpensive purely because its total mass is large.

Ask for the composition. A supplier that has specified it can tell you; one that has not is selling a total mass. See what is in a peptide blend.

The unit-price checklist

• Is net peptide content published? If not, the price per milligram of compound is unknown.
• Is purity published with a method, a wavelength and a lot number?
• For a blend, is the per-component mass stated?
• Is the price the landed price, including duty, tax and brokerage?
• Is analysis included in the price, or would you be paying for it separately?

Answer those five and the comparison becomes arithmetic. Skip them and it stays a guess dressed as a number. For the wider supplier assessment, see choosing a research peptide supplier in Canada.

All products referenced are supplied for laboratory research use only and are not approved for human consumption, clinical, or veterinary use.