The practical answer
Add material subtotal, shipping, nonrecoverable taxes or import charges, payment fees and any extra verification you must buy, then divide by a comparable quantity. For peptides, a stated gross mass is not a comparable quantity unless both lots report net peptide content; leave unknowns visible rather than entering zero.
Evidence, method & source dates ↓The short answer
The sticker price is rarely the decision number. Two things change the ranking most often: verification you have to pay for because a supplier's documents are incomplete, and differences in how much of the stated mass is peptide. Bachem defines net peptide content as the share of peptide relative to non-peptidic material, mostly counterions and moisture, and notes it is not the same as HPLC purity. [1]
All figures below are invented arithmetic, not supplier prices or market estimates. Use your actual written quotations, destination and institutional purchasing rules.
Step 1: landed cost
Assume both quotes are for the same nominal gross mass and both meet your documentation requirements once the listed verification is bought.
| Budget item | Quote A | Quote B |
|---|---|---|
| Material subtotal | $100 | $120 |
| Shipping | $20 | $10 |
| Nonrecoverable charges | $8 | $0 |
| Additional verification | $60 | $30 |
| Total | $188 | $160 |
Step 2: adjust for net peptide content
Now suppose both quotes are for 10 mg gross. Quote A's lot certificate reports net peptide content of 80%; Quote B's reports 60%. Net peptide content is lot-specific, so it must come from the certificate for the lot you would receive, not a catalog page.
Cost per mg of net peptide: A is $188 divided by 8 mg, or $23.50. B is $160 divided by 6 mg, or about $26.67. B was $28 cheaper in landed cost and about 13% more expensive on a content basis. Bachem notes content tends to be lower for peptides rich in basic amino acids and for hydrophilic peptides that absorb moisture, so gaps of this kind are plausible between salt forms and lots. [1]
| Metric | Quote A | Quote B |
|---|---|---|
| Landed cost | $188 | $160 |
| Gross mass | 10 mg | 10 mg |
| Net peptide content (lot certificate) | 80% | 60% |
| Net peptide mass | 8 mg | 6 mg |
| Cost per mg net peptide | $23.50 | $26.67 |
When you cannot normalize
- Content not reported on one quote: compare landed totals only and write 'content basis unknown' next to the result.
- HPLC purity offered instead of content: do not substitute it; purity and content measure different things. [1]
- Different salt forms (for example TFA vs acetate): the non-peptide fraction differs, so gross masses are not comparable.
- Quote expires or currency differs: record quote date, expiry and currency, and convert at a documented rate on one date.
Purchase note checklist
Who this fits: anyone comparing two or more quotes for the same material. Who can skip it: single-source purchases where only one supplier meets the specification. This guide gives no dosing, preparation, administration or human-use calculation; it is purchasing arithmetic only. Source accessed October 29, 2026.
- Quote dates, expiry and currency for each supplier.
- Quantity basis: gross mass and, if reported, lot net peptide content.
- Every cost line, with unknowns marked unknown rather than zero.
- Verification you must buy and why (which certificate line is missing).
- Sensitivity case: for example, verification cost doubles or shipping is re-quoted.
- Person responsible for resolving each open item.
Check the underlying evidence
Sources & review dates
- Bachem: Quality control of amino acids and peptides, a guide ↗Accessed 29 Oct 2026
Sources are documentary evidence. They do not establish firsthand testing of a listed supplier.