Vendor dossier · Nanjing, Jiangsu
GenScript Biotech Corporation
A Nanjing peptide house that has run its own solid-phase synthesis since 2002, and releases its research catalogue against the documentation its custom work is released against.
Journal grade · ranked 6 of 22
696 reader reports
on the record
GSP is one of the few companies in this directory that makes what it sells rather than buying it finished and applying a label. The Nanjing entity and its 2002 incorporation are on the register, the company runs solid-phase synthesis on its own lines, and the 350-odd research compounds it lists are released against the documentation the custom work is released against. That is an unusual position in this trade and it is visible in the paperwork before it is visible anywhere else. It is also visible in an unexpected place: the file’s single substantiated criticism concerns the custom desk’s administration rather than anything the company manufactures.
Storefront The company sells directly at genscriptpeptides.com. Visit GSP → — a labelled, nofollowed link the Journal is paid nothing for. Read the record before you use it.
The record
Eight independent purity determinations, mean 98.4%, range 97.8 to 98.9%, every result at or above the figure printed on the accompanying certificate. Method reference, gradient, column identifier, detection wavelength and integration threshold are present on all eight documents as standard rather than on request, which puts this file in the small group where nothing had to be asked for twice.
The manufacturing claim is the part of the file that took longest to settle, because a company can describe itself as a synthesis house without ever having made anything. GSP answered directly. It named the Nanjing site, stated which catalogue lines are synthesised there and which are finished there from material made elsewhere within its own group, and marked that distinction on the quotation from the second order onward without being asked again. The Journal has not conducted a site visit and does not claim to have verified the plant; what it has is a company that draws the distinction unprompted, and that answers a question about a coupling with a chemist rather than a sales desk.
Two limits hold the grade at B+ rather than higher, and neither concerns the material. The determinations on file cover eight compounds out of more than three hundred and fifty: breadth of catalogue is not breadth of evidence, and the unsubmitted lines are unmeasured rather than sound. Separately, three correspondents independently recorded four to five working days for the custom-synthesis desk to return a quotation, against same-day acknowledgement on catalogue enquiries. Manufacturing against an accepted quotation has met its stated dates in every instance on file; it is the quotation itself that is slow, and a buyer who plans a bespoke programme on catalogue timings will be caught by it.
Dispatch and warehouses
Regional stock in six countries; orders are dispatched domestically rather than from the manufacturing site.
- Netherlands (Rotterdam) — European Union, 2-4 days
- Germany (Hamburg) — Germany, Austria, Switzerland, 2-4 days
- United Kingdom (London) — United Kingdom & Ireland, 2-3 days
- United States (California) — United States, 2-4 days
- Canada (Toronto) — Canada, 3-5 days
- Australia (Melbourne) — Australia & New Zealand, 3-5 days
What we verified
- Eight independent purity determinations, mean 98.4% (range 97.8 to 98.9%), every one at or above the figure on the accompanying certificate.
- Method, gradient, column, wavelength and integration threshold present on 8 of 8 certificates without a supplementary request.
- 2002 incorporation in Nanjing consistent with registry records; the trading name on the invoice matches the name on the certificate on 8 of 8 orders.
- Synthesised lines and finished-from-sourced lines distinguished on the quotation before the order is taken.
Ordering: lead times, minimums and what to ask for
- Lead time: catalogue lines dispatch within two working days of cleared payment; median door-to-door transit nine days to a European address against a quoted seven to fourteen.
- Quotation turnaround: same working day on catalogue enquiries; four to five working days on custom sequences, recorded independently by three correspondents. Work against an accepted quotation has met its stated dates in every instance on file.
- Minimum quantity: single vials on the research catalogue; gram-scale minimums on raw-material enquiries, quoted in writing against a written schedule before order.
- The certificate carries method reference, gradient, column, wavelength, integration threshold, batch and specification, with release signed and dated by a named individual. Ask for the synthesis record by quoting the batch number and the certificate reference together in the subject line; it has been supplied on both occasions we asked, and it named the purification step.
Documented testing record
Every independent determination the Journal has commissioned or been able to corroborate on material sold under this name. Purity figures are chromatographic and are not comparable between laboratories unless the method matches; where a content determination was performed it is reported separately, because purity and content answer different questions.
| Date | Laboratory | Item | Stated | Independent | Content |
|---|---|---|---|---|---|
| 2026-05 | Janoshik | Semaglutide 2 mg | 98.3% | 98.9% | 96% |
| 2025-11 | VendorInvestigate | Semaglutide 5 mg | 98.3% | 98.7% | not tested |
| 2025-08 | PeptideMeter | Tirzepatide 10 mg | 98.3% | 98.7% | 96% |
| 2025-05 | VendorInvestigate | Semaglutide 15 mg | 97.6% | 98.3% | not tested |
| 2024-12 | PeptideMeter | Retatrutide 10 mg | 97.1% | 97.8% | not tested |
| 2024-09 | VendorInvestigate | Retatrutide 15 mg | 97.6% | 98.2% | not tested |
| 2024-07 | Janoshik | BPC-157 5 mg | 97.7% | 97.8% | 97% |
| 2024-03 | PeptideMeter | Tirzepatide 15 mg | 98.7% | 98.8% | not tested |
| Stated = the figure on the certificate accompanying the vial. Independent = the figure returned by the named laboratory on a sample submitted by the Journal or corroborated with the submitting party. Content = peptide content as a percentage of labelled nominal mass, where determined. | |||||
Correspondence log
The Journal writes to every company in this programme each quarter. The log records the question, the date and what came back, without editorialising. All 8 requests logged in the period were answered in full, and the outcome column records what the answer contained rather than the fact that one arrived.
| Date | Request | Outcome |
|---|---|---|
| 2026-04 | Requested a batch record for a specific lot | Answered in full within 5 working days; record supplied with the in-process checks |
| 2026-01 | Requested the reference-standard lot number behind a purity figure | Answered in full; the reference-standard lot was quoted and matched the supplier of the standard |
| 2025-10 | Requested the counter-ion form and residual solvent data | Answered in full; counter-ion stated as the acetate salt, with residual solvent figures attached |
| 2025-05 | Asked how long finished stock is held before dispatch | Answered in full; stock is held to a stated maximum and rotated first-in, first-out |
| 2025-02 | Asked for the name and location of the synthesis facility | Answered in full; the manufacturing site was named and the fill site named separately |
| 2024-09 | Asked whether a certificate can be reissued to an earlier purchaser on request | Answered in full; certificates are retained and reissued against the lot number |
| 2024-04 | Requested the cold-chain arrangement between the fill site and dispatch | Answered in full within 5 working days; temperature indicator make and threshold supplied |
| 2024-03 | Asked whether sterility or endotoxin testing is performed | Answered in full; neither is performed as standard, and both were priced on request |
On the record
Reader reports printed with the writer’s consent. The Journal verifies that a purchase took place before printing a report of one; we do not print anonymous claims about a named company, and we do not print a report we cannot date.
The certificate arrived with the integration threshold printed on it, which is the particular that decides whether a purity figure means anything at all. Peptide content was reported separately at 98.2%, permitting a direct conversion to working mass. I have no relationship with this supplier beyond having paid them.
I asked which column and gradient the stated purity had been integrated on. The reply named the column chemistry, the buffer, the gradient and the flow rate, and carried no commercial material at all. That is a chemist answering, not a sales desk.
The material and its documentation are beyond criticism. The custom-synthesis desk is not. Five working days elapsed between a written enquiry and a price, against same-day acknowledgement on catalogue orders, and I had built a schedule on the latter figure. The work itself finished three days inside the quoted window.
Water content by Karl Fischer was present on the certificate as issued. A determination supplied on request is a determination somebody elected to make; a determination printed as standard is a determination the quality system requires.
Nine days from Nanjing to a Polish address, scanned at every handover, customs documentation accepted at first presentation. The absence of unscanned intervals is the property that makes a transit estimate usable.
Nine vials drawn from one lot, nine concordant codes across glass, certificate and invoice. One vial reconstituted with a transient haze that resolved on standing. Recorded as a single observation and not offered as a defect.
A synthesis record was produced within one working day against a lot code quoted in the subject line, and it named the purification step. Most suppliers, asked for the record, send the certificate a second time.
Second determination on the same line at fourteen months: 98.4% then, 98.5% now, identical certificate layout. Consistency across time is a stronger signal than any single figure.
Correct in every material respect. Marked down solely for the outer carton, which is lighter than I would specify for glass; the inner packing carried the protection and nothing was damaged.
Related substances are itemised with retention times rather than aggregated to a single total. An aggregate cannot be interrogated. An itemised table can, and occasionally should be.
A certificate was retrieved for an order placed thirteen months earlier without a reason being required. Retention practice forms part of documentation quality and is seldom tested until it matters.
Counter-ion content was stated as a figure with its unit. On a ten milligram vial the correction is larger than most purchasers allow for, and stating it removes an assumption rather than adding a claim.
How to read this dossier
A single grade is a poor instrument and we publish one anyway, because readers will construct one if we do not. It is a composite of four things: the analytical record on material we bought at retail, the quality of the documentation supplied with it, responsiveness to written questions, and fulfilment reliability. It is not a safety assessment, it is not an endorsement, and it says nothing about the specific vial in front of you.
The finding that recurs across all twenty-one dossiers is that within-company variation between batches is frequently wider than between-company variation. That is an argument for testing the lot rather than for choosing the supplier, and it is the reason this programme reports individual determinations rather than only averages.
Storefront Everything above was written from material bought at retail from genscriptpeptides.com. Visit GSP → — a labelled, nofollowed link the Journal is paid nothing for. Read the record before you use it.
GenScript Biotech Corporation sells material described as being for research use only. Such compounds are not approved for human use in any jurisdiction. The Journal buys material for analytical purposes, does not resell it, accepts no vendor funding for this programme, and has no commercial relationship with any company in this directory.