Abstract: A flow injection extraction apparatus utilizing a membrane phase separator and constant pressure pumping is described and characterized In terms of extraction coil length, sample injection volume, and flow rates. Equations are derived and verified that show that under conditions where the sample component is quantitatively extracted into the organic phase, the peak area depends only on the number of moles of sample injected and the total flow rate of organic solvent. A sampling frequency of 4 samples/min is readily achieved. Procyclldlne hydrochloride is assayed in tablets with 1% precision and accuracy.