Most people shopping for research peptides look at one number first: purity. A 99% vial feels like a clear win over a 97% one. But there’s another number on a good COA that often matters more, and plenty of people skip right past it. It’s called net peptide content, or NPC.
Two numbers, two different questions
Purity, measured by HPLC, tells you how much of the peptide material is the peptide you actually ordered, instead of near-miss versions like broken or altered chains.
NPC tells you how much of the powder in the vial is peptide at all. The rest is usually water and salts left over from making it. A 10 mg vial with 80% NPC holds about 8 mg of actual peptide.
Let’s run the numbers
Take a 10 mg vial with 80% NPC, so 8 mg of peptide.
- At 97% purity, about 7.76 mg is your target peptide.
- At 99% purity, about 7.92 mg is.
That’s a difference of 0.16 mg. Real, but small.
Now say someone ignores NPC and treats the full 10 mg as peptide. They’re off by 2 mg. That’s more than ten times bigger than the purity gap, and it throws off every concentration, curve, and potency number built on it.
So which one matters more?
Going from 97% to 99% is nice, especially for very sensitive work like reference standards or tight binding studies, or if the impurities happen to be active. But for most everyday research, the bigger risk to your results is not knowing your NPC.
The honest answer is that you need both. Purity tells you what’s in the peptide. NPC tells you how much peptide you really have. A COA that only shows one leaves you guessing on the other.
This information is for research use only.
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