You know how much you have? Like from your vendor? Lets say they told you 500mg.
Now go get a cough syrup cap, a glass, some plastic wrap, and a dropper with measurements.
Take that cough cup, fill it to 5 tsp (25ml) and pour into the glass twice. Now you have 50ml of liquid. Make one of those tsp's be vodka, for purity. So have 9tsp water and 1 tsp vodka
Add all the 2c-e to the water/vodka, it takes a bit to dissolve but it will.
Now use your dropper. You were told you had 500mg, but in case they overshot you, we are gonna pretend its 550mg (+10% in whatever case).
So now you have 550mg in 50ml. 1 ml will contain 11mg of 2c-e.
I have a dropper with .5ml increments and this method works perfectly. Its safe, and stable.
when done with the mix, cover with plastic wrap to avoid evaporation. If evaporation does occur, remember the 2c-e didnt leave, the water did.