Dont keep the extract as salt form from manske precipitation, there is a lot of salt impurity its impossible to know how much there is of alkaloids. The two possibilities I would say you have are, either think of how much rue seeds you had in the first place and divide in the according number of doses (if 3,5g of seeds are 1 dose), or redissolve the precipitate in warm water and add sodium carb and let it precipitate in the fridge for a few hours. The freebase will be much purer than the salt, then you can consider it to be, say, 75% pure or smt like that, depending how it looks, or purer if you redissolve and reprecipitate again