A peptide price comparison tool is a normalization calculator, not a price list. The only number worth comparing across suppliers is cost per milligram of confirmed material, and you get it from four inputs the sticker price hides: label mass, HPLC purity, net peptide content (mass fraction), and landed cost per vial. The formula:
Effective $/mg = (unit price + allocated shipping + allocated verification cost) ÷ (label mg × purity % × peptide content %)
Run three catalog listings through that and the ranking usually changes. Below is the full column layout, a worked three-supplier example where the cheapest sticker finishes last, the five inputs that move cost more than the headline number, and a plain accounting of when building this tool is a waste of an afternoon.
Why price per vial is the wrong unit
A 5 mg vial at $28.00 and a 10 mg vial at $59.00 look like $5.60/mg and $5.90/mg. Neither figure survives contact with the certificate of analysis.
Lyophilized peptide is not shipped as pure peptide. A vial produced by standard solid-phase synthesis and purified by preparative reverse-phase HPLC arrives as a salt — commonly trifluoroacetate — with residual solvent and adsorbed water. Net peptide content typically lands between 70% and 90% by weight, and it varies with sequence: basic residue counts drive counterion load, so an arginine-rich sequence carries more salt mass than a neutral one. A vial labeled 5 mg at 80% content holds 4.0 mg of peptide. At 72%, it holds 3.6 mg. That is a 10% swing in what you actually paid for, and it appears nowhere in the price.
Purity and content are separate measurements answering separate questions. Purity by HPLC area at 214 or 220 nm tells you what fraction of the UV-absorbing material in the injection was your target peak. Peptide content by amino acid analysis or quantitative NMR tells you what fraction of the powder mass is peptide at all.
A 99.2% purity figure by HPLC area is a statement about the chromatogram, not about how much peptide is in the vial. Those are different numbers, and only one of them divides cleanly into the price.
Most suppliers publish purity. Far fewer publish content. A comparison tool that ignores the gap is comparing labels, not materials. Our approach to what appears on a certificate of analysis covers which assays we report and why.
The five inputs that move landed cost more than the sticker
- Shipping, allocated per vial. A $22 domestic shipment across 5 vials adds $4.40 each — 7.5% on a $59 vial. Across 25 vials it adds $0.88, under 1.5%. Order size changes the effective price more than most promotional codes. Cold-chain handling with dry ice adds roughly $35–$60 per shipment; check the shipping terms before you model it.
- Verification cost, amortized per lot. Independent HPLC-UV runs about $85–$175 per sample. LC-MS identity confirmation runs $150–$400. A combined panel with residual solvent and endotoxin can reach $400–$900, with 5–10 business day turnaround. Amortized across a 3-vial buy, a $145 test adds $48.33/vial. Across a 30-vial buy, $4.83.
- Volume tier breaks. Published tiers commonly step at 10 units (8–12% off) and 25 units (15–22% off). If your consumption is 40 vials a year, buying in two 20-unit blocks instead of eight 5-unit blocks changes effective cost more than switching suppliers does. Wholesale tiers are worth modeling explicitly rather than treating as a footnote.
- Lot continuity. Re-ordering the same catalog item from a supplier with no lot traceability means a new synthesis batch with a different impurity profile and different content. If your method requires bridging data between batches, the "cheap" supplier just added an extra qualification run to your budget.
- Payment terms. A 15% discount for direct bank transfer or crypto is not a 15% discount. It is a 15% payment for surrendering chargeback recourse. Price it at whatever your dispute exposure is, not at zero.
The spreadsheet: exact columns
Fifteen columns, one row per SKU per supplier:
- A–C: Supplier, catalog item, lot number if published pre-purchase
- D: Label mass (mg)
- E: Unit price at your realistic order quantity
- F: Purity % from COA (record the detection wavelength — 214 nm and 280 nm give different area percentages for the same sample)
- G: Peptide content % (leave blank if not published; do not guess silently)
- H: Content source — AAA, qNMR, or "assumed"
- I: Order quantity
- J: Shipping total ÷ I
- K: Third-party test cost ÷ I
- L: Net mg per vial = D × F × G
- M: Effective $/mg = (E + J + K) ÷ L
- N: COA date and whether it is lot-specific or a representative document
- O: Mass spec confirmation present (yes/no)
Column H is the one that earns its keep. Two suppliers with identical published purity are not comparable when one reports content by AAA and the other reports nothing. Flag the assumption in the cell rather than burying it in the arithmetic.
Worked example: the ranking flips
Three listings, all for the same nominal material.
- Supplier A — 5 mg, $28.00, 99.1% purity, content not published, $15 shipping across 10 vials ($1.50/vial)
- Supplier B — 5 mg, $34.50, 98.4% purity, 87.2% content by AAA, free shipping over $200
- Supplier C — 10 mg, $59.00, 99.4% purity, 91.0% content by AAA, $22 shipping across 5 vials ($4.40/vial)
Sticker price per label mg: A $5.60, B $6.90, C $5.90. A wins by 5.1% over C.
Normalized, assuming 80% content for A because none is published:
- A: 5 × 0.991 × 0.80 = 3.96 net mg → $29.50 ÷ 3.96 = $7.45/mg
- B: 5 × 0.984 × 0.872 = 4.29 net mg → $34.50 ÷ 4.29 = $8.04/mg
- C: 10 × 0.994 × 0.910 = 9.05 net mg → $63.40 ÷ 9.05 = $7.01/mg
A goes from 5.1% cheaper than C to 6.3% more expensive. And A's number rests on an assumption. If A's true content is 72% — well inside normal range for a TFA salt of a basic sequence — A lands at $8.27/mg, 18% worse than C. The unpublished number is not a rounding detail; it is the widest error bar on the page. Comparative write-ups like our high purity peptides review exist because that error bar is where most sourcing decisions actually go wrong.
When this tool is not worth building
Say it plainly: for most buyers, this spreadsheet loses money.
- Low volume. Building and validating it honestly takes 2–3 hours. On a 4-vial annual spend of roughly $130, a perfect optimization saves $8–$18. You spent $150+ of your own time to find it. Buy from a documented supplier and move on.
- It cannot detect a false COA. The tool ranks arithmetic, not honesty. A supplier can print 99.2% and ship 91%. Nothing in column M catches that. Only an independent injection does, and that costs more than the spread you are chasing on small orders.
- It goes stale fast. Catalog prices, tier thresholds, and shipping tables shift on 30–90 day cycles. A comparison table older than about 60 days is a historical document. Any scraped or automated tool inherits this problem and usually hides it behind a fresh-looking timestamp.
- Optimizing to the cheapest normalized price frequently selects for the worst documentation. The suppliers with the lowest $/mg are often the ones publishing no lot number, no mass spec, and a representative COA reused across batches. You saved 9% and lost the ability to reproduce a result on re-order.
- Purity below your method's floor is worth $0, not "cheaper." If your analytical protocol requires ≥98% and a listing offers 95% at 30% less, that is not a discount — the material fails your acceptance criteria before the first sample injection. Exclude it from the sheet rather than letting it anchor the low end.
- Storage capacity is a hard gate. Bulk buying only pays if you can hold lyophilized material at −20 °C, where typical stated shelf life runs 24–36 months. Without that, a 25-unit tier discount is prepaid degradation.
- Regulated or grant-funded work changes the axis entirely. Where documentation continuity, research-use-only status, and audit trail matter, price rank is close to irrelevant. Switching suppliers to save $0.60/mg while breaking batch continuity is a bad trade you can't undo.
- Cross-border listings are not comparable. International transit adds customs exposure, 10–25 business day variance, and no practical remedy on a seized parcel. A 20% lower price with a 5% loss rate and no reshipment policy is not 20% lower.
Keeping it honest
Two rules make the difference between a decision tool and a decorative table. First, re-price the whole sheet before every purchase over roughly $500 — not once a quarter. Second, log actual received-lot data next to the pre-purchase estimate: COA date, lot number, whether mass spec was included, whether the content figure matched. After six or eight orders the delta column tells you which suppliers' published numbers hold up, which is worth considerably more than the $/mg column ever was.
That log is the part no public comparison tool can build for you, because it is specific to what actually arrived on your bench. If you want the underlying documentation for a specific lot before you model it, contact us with the catalog item and we'll send what exists.
Supplied strictly for in-vitro laboratory research by qualified researchers and institutions. Not a drug, food, cosmetic or dietary supplement. Not for human or veterinary consumption. Not evaluated by the FDA.