peptide purity FAQ

Request a detailed impurity analysis from the supplier. High purity with multiple secondary peaks suggests incomplete purification where several low-abundance byproducts remain. If the supplier cannot identify the impurities or confirm they are inert (e.g., residual TFA, salts), reject the batch. Structurally similar deletion sequences or oxidized variants can compete for receptor binding and confound dose-response curves.

A 25% deviation in lysine content suggests either a deletion sequence (one lysine removed during synthesis) or incomplete hydrolysis during AAA. Request the supplier re-run the AAA or provide an independent third-party analysis. If the lysine deficiency is confirmed, the peptide sequence is incorrect and the batch cannot be used. Lysine residues are often critical for solubility and receptor interaction.

A mass deviation greater than 1 Da suggests either incorrect peptide identity or significant chemical modification. DSIP analogs (acetylated, amidated, or cyclised variants) have different molecular weights. If you ordered standard DSIP but received an analog, the biological activity will differ. Contact the supplier immediately with the specific mass observed and request either a replacement batch or confirmation of the actual peptide structure. Do not proceed with experiments using misidentified peptides.

Request a re-analysis with a fresh column or a different solvent gradient. A drifting baseline means the purity calculation is unreliable. Impurities may be hidden under the drift, artificially inflating the target peak percentage. If the supplier cannot or will not rerun the analysis, consider the peptide suspect and do not use it in experiments where purity directly affects the outcome (dose-response curves, receptor binding assays, mechanistic studies). Baseline drift of more than 5 mAU (milliabsorbance units) over the chromatogram duration is a red flag.

Without third-party accreditation, the COA is vendor self-certification. It holds no independent verification. Request documentation of the testing lab's ISO 17025 certificate, including the scope of accreditation and the accreditation body (ANAB, A2LA, UKAS). If the vendor can't provide this, the COA is unreliable. For critical research applications, consider sending a sample to an independent analytical lab for confirmatory testing before committing to full-scale experiments.

This indicates methionine oxidation, which is reversible under some conditions but may affect peptide stability and bioactivity. Contact the supplier to confirm whether the peptide was synthesized with oxidation or if it occurred during storage. Methionine-containing peptides should be stored under argon or nitrogen to prevent further oxidation. If the oxidation occurred before shipping, request a replacement batch synthesized and stored under inert atmosphere.

This signals the peptide was synthesized months ago and has been in storage. Potentially at non-ideal temperatures. Lyophilized peptides are stable at −20°C for 12–24 months, but stability degrades rapidly if stored at ambient temperature or subjected to freeze-thaw cycles. Request the storage conditions log from the supplier. If they cannot confirm the peptide was stored at −20°C continuously, request a fresh batch with a current COA. Peptide degradation is cumulative and irreversible. Starting an assay with partially degraded material guarantees inconsistent results.

The peptide identity is correct, but impurity levels are too high for reliable research. MS confirms you received survodutide, not a different compound, but 8% impurities mean nearly one in twelve molecules is something else. Enough to skew receptor activation studies, particularly at low concentrations where impurities represent a larger fraction of the active dose. Use this batch only for preliminary method development, not for data collection. Order a higher-purity replacement for actual experimental work.

Do not use it until you obtain endotoxin data. Contact the supplier and request LAL (Limulus Amebocyte Lysate) testing for your specific batch. If they cannot provide it, either send a sample to a third-party testing lab for independent LAL analysis (cost: approximately 150–300 USD per sample, turnaround 5–7 days) or accept that the peptide is unsuitable for cell-based work. Endotoxin contamination as low as 0.5 EU/mg can alter cytokine expression, immune cell activation, and apoptosis rates. Rendering your results uninterpretable.

Reject the batch. The purity percentage is calculated from peak areas, but if multiple peaks exceed 10% relative intensity, you're working with a mixture where the 'impurities' represent significant contamination with structurally similar peptides. Likely deletion sequences or oxidized variants. These won't separate cleanly in your assay and will produce inconsistent dose-response data. Request a replacement batch with a chromatogram showing one dominant peak above 95% and all other peaks below 3%.

The peptide is correctly synthesised but incompletely purified. The 8% impurity consists of structurally similar peptides (deletion sequences, protected amino acids, or truncated forms) that don't affect molecular weight enough to shift the MS base peak but do appear as separate HPLC peaks. For some applications (screening assays, preliminary dose-finding), 92% is acceptable. For quantitative work (IC50 determination, structural studies, pharmacokinetics), it's not. The impurities introduce variability you can't correct for. Use it only if you can verify the impurities are biologically inert in your specific assay.

Request it in writing before placing the order. Reputable suppliers include chromatograms as standard. If they refuse, the purity claim is unverifiable and the material should not be used for publication-quality research. Some suppliers charge $50–$150 for third-party HPLC re-testing; this is a reasonable cost to confirm material integrity before starting a 12-week assay. If cost is prohibitive, consider switching to a supplier that includes full analytical data as standard. The long-term cost of invalidated research far exceeds the upfront cost of verified material.

A +10 Da shift often indicates an acetylated N-terminus or a sodium adduct (Na+ replaces H+ on the peptide, adding 22 Da per substitution). Acetylation is intentional in some peptides (acetyl-hexarelin, for example) but unintentional in others. If acetylation was not specified in the product description, contact the supplier for clarification. Acetylated peptides have different receptor binding affinities and half-lives than non-acetylated forms. Sodium adducts are cosmetic and do not affect biological activity, but their presence signals suboptimal desalting during purification.

Request the chromatogram and examine the peak shape. If the 96% purity reflects a single dominant peak with minimal shoulders, it's usable for non-critical applications. If the chromatogram shows multiple large secondary peaks, the remaining 4% is a mixture of deletion sequences or aggregates that could interfere with receptor binding assays or dose-response studies. For competitive binding studies or structure-activity work, 96% purity introduces too much uncertainty. Request a re-synthesis or choose a supplier with ≥98% purity standards.

A 3 Da shift indicates a synthesis error. Likely an amino acid substitution or an extra acetyl group from incomplete deprotection during synthesis. This is not AOD-9604. The peptide may have similar chromatographic behaviour (explaining why HPLC purity looks acceptable), but the biological activity will differ from the published literature on AOD-9604. Reject the batch and request mass spectrometry confirmation before accepting a replacement.

This is standard practice when a single order spans multiple synthesis batches. Especially for high-demand peptides. Each vial should have its own COA corresponding to its specific lot number. Do not assume both vials have identical purity. Batch-to-batch purity variation of ±1–2% is normal even from the same supplier. If you're running parallel assays, use vials from the same lot to eliminate batch variability as a confounding factor. If that's not possible, document the lot numbers in your methods section and test for inter-batch consistency before proceeding.

Multiple peaks indicate the presence of impurities. Truncated peptide sequences, synthesis byproducts, or degradation products. Calculate the purity yourself by dividing the area of the DSIP peak (usually the tallest peak at the expected retention time) by the total area of all peaks. If smaller peaks collectively exceed 5% of total area, the sample purity is below research grade. Peptide fragments and deletion sequences can interfere with receptor binding assays, so samples with complex chromatograms should be re-purified or replaced.

You're working with 22% excipients. Likely residual acetate salts or TFA (trifluoroacetic acid) from synthesis. If the vial is labelled as 5mg AOD-9604, the actual peptide mass is approximately 3.9mg. Reconstituting as if the full 5mg is active peptide will underdose every experiment by roughly 20%. Recalculate all reconstitution volumes based on the reported peptide content percentage, or request a batch with ≥85% content to simplify dosing math.

Do not use this peptide in vivo or in immune cell cultures. Endotoxin levels above 1.0 EU/mg can activate Toll-like receptor 4 (TLR4) signaling pathways, triggering cytokine release that will confound any immune-related assay or metabolic study. For in vitro work with non-immune cell lines, it may be acceptable if endotoxin response isn't a study variable. But it's still a signal of poor purification quality. Request a replacement batch or filter the reconstituted solution through a 0.22 micron filter to remove endotoxins before use.

'Negative' without a quantitative EU/mg measurement is insufficient for biological research. Contact the supplier and request the actual LAL assay result in EU/mg. If they can't provide a number, the batch wasn't tested properly. Assume endotoxin levels are unknown and either send a sample for independent testing or reject the batch. For in vivo metabolic studies using survodutide, undocumented endotoxin contamination is the most common cause of unexplained inflammation and inconsistent results.