Asking directly, because I could not find a straight answer: Attributing a new peak: degradation product or excipient? Posting the method first, because I know what the first three replies will otherwise be. Column: C18, 3.0 x 150 mm, 2.6 um Mobile phase: 0.1% TFA in water / 0.1% TFA in acetonitrile Gradient: 5% to 52% organic over 27 minutes Detection: 214 nm Injection: 15 uL Sample: tirzepatide, reconstituted to 1.0 mg/mL, injected within an hour The main peak integrates at 96.2% 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.

Analytics · Impurities & related substances

Attributing a new peak: degradation product or excipient?

Analytics › Impurities & related substances counter-ion content HPLC data table forced degradation

Solved Closed

Solved by Ostrowski in post #2

Acetate content: counter-ion content. Trifluoroacetate or acetate from the salt form of the peptide. Affects mass calculations and should be stated on a complete certificate.

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s.hartmannTL2 Moderator17 Jan 2025#1

Asking directly, because I could not find a straight answer: Attributing a new peak: degradation product or excipient?

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

Column: C18, 3.0 x 150 mm, 2.6 um
Mobile phase: 0.1% TFA in water / 0.1% TFA in acetonitrile
Gradient: 5% to 52% organic over 27 minutes
Detection: 214 nm
Injection: 15 uL
Sample: tirzepatide, reconstituted to 1.0 mg/mL, injected within an hour

The main peak integrates at 96.2% 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.

0 likes 18mo

OstrowskiTL2Member Solution27 Jan 2025#2

Acetate content: counter-ion content. Trifluoroacetate or acetate from the salt form of the peptide. Affects mass calculations and should be stated on a complete certificate.

8 likes 18mo

w.moreauTL2 Moderator4 Feb 2025#3

Ostrowski, post #2: Acetate content: counter-ion content. Trifluoroacetate or acetate from the salt form of the peptide. Affects mass calculations and should be stated on a complete certificate. Go to post

post #2 is right about the mechanism and I think understates the practical bit.

Related substances: compounds chemically related to the target peptide but not the target peptide itself. The standard method separates them and reports them as area percent. How related they can be before they exceed specification is a regulatory question.

7 likes in reply to #2 18mo

Promoted into the documentation commons. The content of this topic is maintained at Counter-ion content and its consequences, with named maintainers and a review date. The promotion was discussed in doc review. Corrections are best raised against the document, which is the version that gets kept current.

This topic was closed 60 days after the last reply. Closing is automatic for quiet topics so that a settled answer does not collect new questions underneath it. If you have a follow-up, open a new topic and link back to this one — that keeps both readable and gives your question its own title.

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