Purity A 🧵

At it’s core, purity should detect the peptide and closely related degradation products We do heat degradation since that’s the most likely cause for degradation, but throw in acid/base if the peptide is pretty resistant to heat

Next, it might catch an excipient (filler) or unknown compound by chance. We see this randomly - we’ve found phenol and m-creosol as preservatives. Why by chance? The methods weren’t developed for these compounds - so it’s pure luck.

What it’s definitely not: “The vial is 99.8% pure, so there is only 0.2% other stuff in the vial.” That vial probably has 2-400mg of powder in it, and 10mg of it is your peptide. The rest is probably lyophilization sugars, buffers, and sometimes preservative.

The lab giving you the lowest purity result has the best method for purity on that peptide. The lab giving you the highest purity result has the worse method for purity on that peptide. Applies if two, four, or six labs have a higher purity result - all have worse methods.