Second pass at: Buffers, pH and why a formulation is a formulation

Second pass at: Buffers, pH and why a formulation is a formulation Writing it up because I had to work it out twice and would rather nobody else did.

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

A Janoshik report on a retatrutide lot gives 97.1% purity. The supplier certificate for the same lot states 98.3%. 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?

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

post #9 answers the question as asked. The question underneath it is different.

Antioxidants: compounds that prevent oxidation (which damages peptides) are sometimes included. Methionine oxidation is a common degradation pathway and antioxidants help prevent it.

Picking up post #14: that is the part I would want checked first.

Antioxidants: compounds that prevent oxidation (which damages peptides) are sometimes included. Methionine oxidation is a common degradation pathway and antioxidants help prevent it.

post #21 answers the question as asked. The question underneath it is different.

Isotonicity: an isotonic solution has the same osmotic pressure as blood. Non-isotonic solutions can cause discomfort on injection. Injectable peptide solutions are formulated to be isotonic.