Coming back to: Adsorption to container surfaces and to plastics

Adsorption to container surfaces and to plastics — setting out what I have, and where I think it stops being reliable.

Posting the method first, because I know what the first three replies will otherwise be.

• Column: C8, 4.6 x 150 mm, 3.5 um
• Mobile phase: 0.1% TFA in water / 0.1% TFA in acetonitrile
• Gradient: 10% to 49% organic over 35 minutes
• Detection: 220 nm
• Injection: 15 uL
• Sample: semaglutide, reconstituted to 2.0 mg/mL, injected within an hour

The main peak integrates at 97.8% of total area. There is a small feature on the trailing edge that I cannot decide is a shoulder or a baseline artefact, and that is what I am actually asking about.

Picking up the opening post: that is the part I would want checked first.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

On the opening post — agreed on the reasoning, with one qualification.

Excipients and their purposes: mannitol, sucrose, or other sugars in lyophilised formulations protect the peptide during drying and storage. They are not impurities; they are functional components.