All you need to do is to concentrate the methanolic fraction to dryness on rotar vapor and re-dissolve or suspend in distilled water and put in a suitable separating funnel. The n-butanol to be added may be saturated with distilled water to enhance its extractability in another separating funnel before adding to the suspended aqueous fraction. Shake the mixture thoroughly and release pressure intermittently and allow to settle down and collect the one on the upper layer of the separating funnel as your n-butanol fraction and the lower portion is the remaining aqueous layer.