The molecule we identify.
The assays we run on PT-141.
The failure modes we see most.
- 01Ring-opened linear PT-141. The cyclic structure can hydrolyze during synthesis or storage to a linear form with +H₂O (+18 Da). The linear form is mass-distinct and biologically less active — LC-MS identifies which is in the vial.
- 02Truncations at the N-terminus or C-terminus. Look for related-peptide peaks at RT - 0.3 to RT - 0.8 min of the main peak.
- 03Net Peptide Content gap. Research-grade variability is wide; 65-90 % NPC across vendors.
- 04Endotoxin contamination. Smaller cyclic peptides are easier to purify than linear ones, but injection-grade still needs LAL.
- 05Storage degradation in solution. PT-141 in BAC water shows main-peak intactness for 21-28 days at 4 °C; longer storage shows linear-variant accumulation.
Transparent panels for PT-141.
Identity (LC-MS) + HPLC purity % + Net Peptide Content. Baseline COA — public + accession #.
- Identity (LC-MS/MS)
- HPLC purity % + impurity peaks
- Net Peptide Content
- Public COA + accession #
- 5-7 day turnaround
COA Essentials plus USP <85> endotoxin (LAL) and USP <71> sterility. The injectable-grade package.
- Everything in COA Essentials
- Endotoxin (LAL) USP <85>
- Sterility USP <71>
- Conformity Testing +1
- 5-7 day turnaround
Plus heavy metals (ICP-MS, USP <232>) and USP <61> bioburden. The full vendor / compounding COA.
- Everything in Injectable Safety
- Heavy metals (ICP-MS) USP <232>
- Bioburden (USP <61>)
- 5-7 day turnaround
PT-141 testing — the common questions.
Why is the cyclic structure of PT-141 important?+
The biological activity of PT-141 depends on the cyclic conformation. The linear ring-opened form has the same amino acid sequence but with the ring hydrolyzed open (+H₂O); receptor binding affinity is significantly reduced. Visual inspection of a vial cannot distinguish cyclic vs linear PT-141. LC-MS, which catches the +18 Da difference, is the tool that identifies which form is in the vial.
How is PT-141 different from melanotan II?+
Both are melanocortin receptor agonists, but PT-141 (Bremelanotide, 7-residue) is FDA-approved as Vyleesi for hypoactive sexual desire disorder. Melanotan II (similar 7-residue cyclic peptide with a different sequence) is not FDA-approved and is marketed as a tanning peptide. Different sequence, different receptor selectivity, different pharmacology. LC-MS distinguishes them by molecular ion mass.
What's a reasonable NPC for research-grade PT-141?+
Industry-typical 78-88 %. Below 75 % indicates excess counter-ion or residual moisture. Above 90 % is uncommon for TFA-salt material. NPC is the dose-accuracy metric independent of HPLC purity.
Does PT-141 need to be tested for purity if it's compounded?+
Yes — compounded PT-141 from compounding pharmacies has wide variability across compounders. We've tested batches from major US compounding pharmacies that ranged 88-97 % HPLC purity. The compounder's certificate of analysis is generally reliable, but independent verification matters when dose accuracy or safety is critical.
What sample size do you need?+
COA Essentials ($189): single 2 mg sealed lyophilized vial. Injectable Safety ($499): same single vial. Vendor Full QC ($749): two additional vials for the destructive sterility and endotoxin tests. Send original sealed vials by overnight courier.
Can you test reconstituted PT-141?+
Yes. Ship the reconstituted vial cold-packed in original BAC water or sterile saline. Reconstituted material is what the user actually exposes themselves to, so testing it directly is the most meaningful version of the assay. Pricing matches the lyophilized vial panel.
Other melanocortin receptor agonist (mc4r) testing —
GLP-1 receptor agonist (Ozempic / Wegovy active). Different receptor family, same HPLC + MS bench.
Repair peptide. Linear sequence (vs cyclic PT-141). Same identity + NPC methodology.
Full peptide menu — all bundles, panels, and compounds we cover.
Verify the cyclic structure. Sign the COA.
HPLC purity, LC-MS identity (cyclic vs linear), NPC, TFA, endotoxin, sterility — Houston bench, public COA.