Preparation of emulsions of methanol extracts
Different solvents were initially tested to see which one
was giving a homogeneous mixture and methanol was found to be
the best. Stock solution of 200 mg/ml of each of the stem and root
bark (8 g each) extracts were made in methanol (40 ml). About 5%
w/w (0.4 g) of Tween 80 (Polyoxyethylene (20) sorbitan
monooleate with 65 hydroxyl number and 45.55 saponification
value) was added to homogenize the solution. Previously, Liu et
al., 2003 reported that methanol do permeate Anopheles gambiae
peritrophic membrane; the small amount swallowed by larvae in
the process of feeding is therefore easily extruded from the gut.
Tween 80 is unlikely to be toxic to humans at the concentration
used since it is used in pharmacological preparation of most drugs
(Ten Tije et al., 2003).