Here is an excellent article on peptide purity written by the business partner of the founder of peptidetest.com:
Updated: 19-Jul-2024 Council On Harm Reduction - Peptide Safety Basics The Council on Harm Reduction (CoHR) for peptides
trustpointeanalytics.com
It goes into detail about what these purity numbers mean, and what they do not mean.
Specifically, a 99.575% purity result does *not* mean that 99.575% of the contents of the vial is the claimed substance, and only 0.425% is anything else.
All it means (to oversimplify a bit) is that only 0.425% of the contents is similar to *but not quite* the claimed substance.
The purity process that is being used (HPLC) does not detect substances that are radically different from the claimed substance. For instance, if a vial contained 20mg of perfectly pure tirzepatide and 10mg of arsenic, the HPLC purity test would report it as 100% pure because arsenic is not similar to tirzepatide. The equipment cannot be set to look for everything.
In addition to not detecting significantly different substances the purity score also says nothing about sterility.
Since a 30mg tirzepatide vial could be half poison and biologically contaminated and still get a 99.5% purity reading the question “why do we care about this purity number” is an excellent question.
My answer is simple: We do not have a better test.
I use purity as a proxy, hoping that a lab that does the work to produce a high quality peptide will also do the work to produce a sterile and uncontaminated product.