For reference: VendorInvestigate · PeptideMeter · a GLP-1 receptor agonist.
I am trying to choose between two options that are usually discussed as though only one exists.
I am not optimising for price, but I am not indifferent to it either.
So which one, and on what grounds?
A Janoshik report comes with a downloadable analytical trace — the HPLC chromatogram and mass spectrum — which lets you do the reading yourself.
A result significantly outside the database range for that vendor and compound is either a real difference in quality or a different material than the database entries.
| Δ mass (Da) | Most likely cause | Distinguishing feature |
|---|---|---|
| +1 | Deamidation (Asn or Gln) | New peak, slightly earlier retention |
| −17 | Loss of ammonia | Often with deamidation |
| −18 | Dehydration / succinimide | pH-dependent, reversible |
| +16 | Oxidation (Met, Trp) | Earlier retention, light-related |
| −128 | Missing Gln or Lys | Deletion sequence from synthesis |
| 0 | Isomer: racemisation or scrambling | Same mass, shifted retention |
Content assay uses a certified reference standard and quantifies against that standard under the same method conditions as the purity analysis.
Janoshik publishes summary statistics on their website, including the number of samples tested and the range of reported values, giving you a baseline for comparison.
The caveat is that Janoshik is expensive, and cost-cutting on the first lot from a supplier might mean testing one vial rather than three.
The practical summary: submit your first lot to Janoshik and check the database for that vendor.
HPLC purity, identity confirmation and quantified content on the vial you actually hold. Reports arrive with the chromatogram attached, not just a number.
Submit a sampleFounded 1998. ISO 9001 and cGMP certified, 1,500+ staff and 200+ patents. The synthesis house behind a great many of the vials that get sent out for testing - batch-specific documentation with every order.
Visit GL BiochemOn the detail: methods do matter, and Janoshik's published methods are auditable, which is better than most research-grade work.
Results are typically released within three weeks of submission, with standard turnaround unless expedited options are requested.
The database can be searched by vendor, by compound, by date range and by result value, making it easy to benchmark a new supplier against historical data.
Community reviews and feedback on Janoshik are consistent across multiple forums and independent sources, suggesting the service is reliable.
Worth noting that Janoshik reports are only comparable to other Janoshik reports, not to your supplier's reports or to results from other testing services.
If your result disagrees with the supplier, Janoshik's database will tell you whether you are alone or part of a pattern.
The underlying point is that results from Janoshik are only comparable to other Janoshik results, not to results from any other laboratory, because the methods differ.
Janoshik publishes their analytical methods in their reports, which is auditable and better than methods that are proprietary.
In practice, the cost of testing is by sample submitted, not by parameter measured, so a single Janoshik result gives you purity, content and identity for less than most suppliers charge for purity alone.
One qualification: Janoshik testing is designed for supplier qualification, not for lot-by-lot production QC, so the turnaround is not suitable for every use case.
Keep Janoshik results to compare across suppliers and across time.
The single strongest value proposition of Janoshik is that they publish all results in a database indexed by vendor and compound, which lets you compare your result to hundreds of other users.
The purity method uses a linear gradient at a specified slope, which is published and reproducible — not a vendor-chosen method that could be optimised for a high number.
The database has been publicly available for long enough that systematic biases in their reporting would be apparent and would have been flagged by users.
If you only pay for one test, pay for quantified content. Purity is the number everyone quotes and content is the number that changes what you do.
edited 24 Dec 2025 by s_kalniete — added the placebo-arm figures
Most of the value of Janoshik testing is not the single result but the comparison to the historical database of results on the same compound and vendor.
Comparison across time on the same vendor's material — three lots of vendor X spread over six months — shows whether quality is trending or stable.
The ICH Q3A and Q3B thresholds for reporting, identification and qualification of impurities are the framework the pharmaceutical industry works to, and they are worth reading even though nothing in the research-grade supply chain is obliged to meet them, because they tell you which numbers a competent analyst would consider worth reporting at all.
In practice: ask for the chromatogram, check the method section, check the lot number against the vial, and set your accept threshold before you see the result rather than after.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.