The particulars: oral semaglutide · 10 mg/mL.
I would rather understand the derivation than memorise the outcome.
Two people I asked gave two answers that differ by a factor of ten, which is suggestive.
Can someone walk through the arithmetic step by step?
10 mg/mL is 10000 µg/mL — roughly 1000 times the concentration at which surface adsorption is measurable. Losses to glass and plastic matter in the low microgram-per-millilitre range, where a monolayer on the wall is a real fraction of what is in solution. At 10 mg/mL that same monolayer is a rounding error. If you see an apparent loss at this concentration, suspect the dilution step or the assay before you suspect the wall.
Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.
Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.
| Pathway | Dominant when | Detected by |
|---|---|---|
| Deamidation | Solution, neutral to alkaline pH | RP-HPLC, +1 Da on MS |
| Oxidation | Light, trace metals, peroxides | RP-HPLC, +16 Da on MS |
| Hydrolysis | Solution, extremes of pH | RP-HPLC, fragment masses |
| Aggregation | Agitation, interfaces, high concentration | SEC, visual haze; often invisible on RP-HPLC |
| Freeze-concentration damage | Freeze-thaw of buffered solution | SEC, loss of recovered content |
Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.
Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.
Sequence determines which pathways apply, so general statements are general.
Cold, dry, dark, still. Those four words cover most of the mitigation.
Aggregated, published test results and vendor ratings built from submitted batches. Methodology stated, dataset browsable, no listing fees.
Browse resultsAnswering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.
Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.
Freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.
Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.
Sequence decides which pathways are even available. Check the residues.
Asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.
Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.
The part that matters: light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.
At dilute concentrations, suspect adsorption before you suspect chemistry.
edited 26 Aug 2025 by halvard_ness — removed a claim I could not source
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.