core peptides FAQ

Different results with a new peptide batch indicate either a purity discrepancy, an impurity profile shift, or a difference in aggregation state that wasn't captured by standard HPLC analysis. Request advanced characterization from your core peptides alternative, including circular dichroism spectroscopy to verify secondary structure, dynamic light scattering to detect aggregation, and peptide mapping to confirm post-translational modification absence. If the new supplier's peptide still underperforms, the issue may be formulation-related. Lyophilization conditions, excipient selection, and storage buffer composition all affect peptide stability and biological activity in ways that purity percentages alone don't reveal.

File a protocol amendment with your IRB or regulatory body documenting the supplier change, and include the new supplier's 503B registration, facility inspection records, and a side-by-side comparison of certificates of analysis showing equivalent purity and sequence accuracy. Most review boards require preliminary validation data demonstrating that the core peptides alternative produces identical biological activity in your specific assay before continuing the study with new material. This validation phase typically involves repeating key experiments from the study's early phases using the new supplier's peptide alongside archived samples from the original supplier. Expect two to four weeks of additional lab work before resuming the main protocol.

Custom synthesis is standard practice for research-grade peptide suppliers, but timeline and cost vary significantly based on sequence complexity. Peptides under 20 amino acids with standard L-amino acids typically require four to six weeks for synthesis, purification, and full characterization. Sequences involving D-amino acids, non-natural residues, or complex cyclization require specialized synthesis protocols and may extend timelines to eight to twelve weeks. Real Peptides handles custom orders with the same third-party verification and documentation standards as catalog compounds. Request a formal quote that includes synthesis timeline, expected purity range, and which analytical methods will be used for characterization.

Request MALDI-TOF MS confirmation from your supplier before starting experiments, even if it costs extra. Sequence microheterogeneity is the most common hidden variable in failed replications. A peptide that's 96% pure by HPLC but contains 8% sequence variants will produce 10–20% lower activity in receptor-binding assays compared to a 98% pure peptide with confirmed sequence fidelity. If Real Peptides provides MS data showing your batch matches the expected molecular weight within 0.5 Da and Core Peptides only provides HPLC purity, you've eliminated the supplier variable. If both match, the replication issue is methodological or biological, not chemical.

Verify oxidation-state testing before purchase, especially if storing reconstituted peptide for more than 48 hours. Methionine oxidation to methionine sulfoxide and cysteine oxidation to disulfide-bridged dimers reduce biological activity by 40–80% but co-elute with native peptide on most HPLC gradients, appearing as part of the main '98% purity' peak. Real Peptides tests for oxidation products in methionine- and cysteine-containing peptides using MS; Core Peptides does not unless requested. For oxidation-prone peptides like GHK-CU, where the cysteine residue is critical for copper binding, oxidation-state confirmation isn't optional. It's the difference between a functional peptide and an expensive inert powder.

Choose Core Peptides for cost efficiency and faster turnaround. Screening studies tolerate the 10–15% activity variability introduced by sequence heterogeneity and batch-to-batch purity drift because you're identifying hits based on relative activity differences, not absolute EC50 values. The lower per-gram cost allows larger compound libraries, and the 5–7 day lead time keeps screening timelines on track. Just don't use the same peptide lot for follow-up dose-response validation. Order fresh from a supplier with tighter batch control once you've identified lead candidates.