Anyone? Looking to make a solution with this soon. Can I use 40% vodka or do I need PG? Or Everclear?
I would probably recommend the PG or Everclear... though it all depends on the concentration you want to reach.
There isn't exactly a lot of data available on 3-OH-phenazepam, but there is literature on its closest analogue, lorazepam.
Turns out the water solubility of lorazepam is .08 mg/ml. Yes, that's just 80 micro(!)grams per ml of water.
A 40% ethanol/water mixture solubilizes around 2 mg/ml of lorazepam, with higher concentrations of ethanol being able to dissolve exponentially more.
Consequently (to account for the possibility of 3-OH-phenaz being less soluble than loraz), I would suggest getting something stronger than 40% ethanol.