Thank you for sharing! It is very useful info to understand especially when we talk about HGH. Because seller claiming about 99.9 % purity of blue-red-brown-grey-green-round-square tops dont know what he is saying or simply say untruth.
First of all, even the highest quality Saizen or Serostin has only 98.5-99 % purity.
Also, important to mention that trying to increase purity of HGH above 99 % will damage growth hormone or any other structure with peptide bonds.
HGH is just as an example. All stated above is about all substances with peptide molecular bonds.
The method of analysis you described is good to measure purity but chromotography is good for this purpose too.