Analytics · HPLC & UHPLC

Theoretical plates: useful number or ritual?

Analytics › HPLC & UHPLC system suitability data table HPLC UV & DAD detection gradient method

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Solved by a.vestergaard in post #3

I read the opening post twice before replying, because I had assumed the opposite. Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing. The correction was fair and I had been repeating something I had not checked carefully enough.

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mira.patelTL4 Admin11 Jul 2025#1

Theoretical plates: useful number or ritual? I have a specific reason for asking rather than idle curiosity, and the context is below.

I would like to understand what this number means before I repeat it anywhere.

A Janoshik report on a tirzepatide lot gives 99% purity. The supplier certificate for the same lot states 97.7%. Both documents name a reversed-phase method; neither states the same gradient.

My question is not "who is right". It is: given that those two figures were produced by different methods, what is the largest difference I should expect from method alone, and at what point does a gap stop being explainable that way?

31 likes 13mo

aliquot_lineTL3Regular4 Sep 2025#2

Area percent is not mass percent. It is a proportion of absorbance, weighted by each species' extinction coefficient. For closely related impurities the approximation is usually good. For structurally dissimilar impurities it can be poor.

6 likes 11mo

a.vestergaardTL2 Moderator Solution13 Oct 2025#3

I read the opening post twice before replying, because I had assumed the opposite.

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

7 likes 9mo

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