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c/hplc·submitted 2 months ago by u/dilara_nyberg

someone explain purity to me like I have not read a paper in years

Questionbranch of 6 comments

Slightly embarrassed to be asking this, but: someone explain purity to me like I have not read a paper in years. Sent the same vial to Janoshik and VendorInvestigate. 99.2% against a claimed 98.5%. The difference was the gradient, not the material. Why two honest labs report different numbers on the same vial. Start…

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6 comments, started 2 months ago
u/naomi_antonsen239 points·2 months ago·edited

A shoulder that does not baseline-resolve cannot be quantified honestly. You can report it as an unresolved shoulder, which is useful information, or you can develop the method until it resolves.

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[removed]97 points·2 months ago

[removed by moderator]

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u/rina_bergstrom53 points·2 months ago

Disagree. Inter-lab spread of a point or two on this assay is ordinary and calling it a discrepancy misleads people.

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u/dilara_nyberg0 points·2 months ago

Disagree.

Agreed. And the corollary is that the method line on a certificate is not decoration, it is the number’s provenance.

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u/dilara_nybergOP120 points·2 months ago

Is that baseline drawn by the software or by hand?

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u/sofia_petrescu81 points·2 months ago

That is area percent, not mass percent. The trace cannot give you the second one.

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The analytical deep end: RP-HPLC methods, gradient design, integration decisions, LC-MS confirmation, amino-acid analysis, water content, and why two labs can report 98.1% and 96.4% on the same vial and both be right. Post the chromatogram, not the summary line.

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