Here is what I recieved from Alkemist Labs in response to your questions.
"The t-Resveratrol standard that we used for our analysis was purchased
from Chromadex (Lot #18090-601) and came with its own C of As:
The *hplc purity* was listed at 99.9%: this is a reflection of
organic impurities that might be present or not with the analyte of interest
The *adjusted purity* was listed at 90.7%: this account for any
water & residual solvents trapped within the powder.
The
adjusted purity equals (100% - % water - % residual solvent) x hplc % purity
These above purities aren’t based on Alkemists’ analysis or
calculations. They are provided by the supplier of primary standards
(Chromadex here). You might be more familiar with company such as Sigma
which sells fine chemicals. Sigma will provide you only with min % hplc
purity but no information on moisture content which render these
chemicals less suitable for use as reference standard in quantitative
hplc analysis.
Regarding your test sample, it was handled the exact same way as the
reference standard (with ptfe filtration). The 87% result represent the
% weight content of Resveratrol in your powder based on a calibration
curve created with the reference standard from Chromadex."
Feel free to call or email with any further questions
Sounds like I got myself I new standard vendor