depends on the pH.
paraffins are large aliphatics, which engage exclusively in VDW interactions. alkaloids are easily separated at low pH, hence the acidification step.
I know that's not what you wanted to hear, but that's the chemistry.
the other option is to exploit physical properties...m.p. (refrig/freeze), molecular weight (centrifugation)
"Nothing is true, everything is permitted." ~ hassan i sabbah
"Experiments are the only means of attaining knowledge at our disposal. The rest is poetry, imagination." -Max Planck