The following procedure is typically followed when performing an acid-base extraction for a mixture containing an acidic and/or basic compound:
#The mixture of compounds is dissolved in a suitable organic solvent, such as dichloromethane or diethyl ether.
# The solution is added to a separatory funnel. If the desired compound is basic, the solution will be washed with aqueous acid (e.g. 5% HCl); if it is acidic, the solution is washed with aqueous base (e.g. 5% NaOH).
# The fractions are then shaken and the two phases are separated. The separatory funnel must be vented frequently to alleviate pressure build-up, especially when containing aqueous solutions that evolve carbon dioxide gas upon neutralization (such as sodium bicarbonate).
# The fraction containing the analyte of interest is then collected. Typically, this is the aqueous layer, as addition of acid or base has caused the analyte to become charged and highly soluble in the aqueous layer. The identity of the aqueous layer depends critically on the organic solvent's density. Organic solvents with a density greater than 1.00 g/mL (e.g. dichloromethane) cause the aqueous layer to float to the top, while solvents with a density lower than 1.00 g/mL (e.g. ether) cause the aqueous layer to sink to the bottom.
# The organic fraction is added to the separatory funnel again, and steps 2-4 are repeated twice more to maximize the yield of the extraction. On the final rinse, a brine solution drives any remaining aqueous solution out of the organic layer.
# If the remaining organic layer contains no analytes of interest, it is discarded; otherwise, the solvent is dried over a suitable drying agent  (such as anhydrous sodium sulfate), filtered, then evaporated under reduced pressure to yield the pure compound.  If the aqueous layer contains the analyte of interest, it is adjusted to the opposite pH (e.g. basic to acidic). Steps 1-4 are repeated with this fraction using an aqueous solution of opposite pH (e.g. NaOH to HCl).  This circular procedure is performed since it is typically much easier to remove organic solvent via rotary evaporation than aqueous solvent.