Microfluidic devices are highly efficient in providing higher mass transfer rates due to the enormous interfacial area created by the high surface-to-volume ratio. Droplet flow microfluidic devices can serve as an efficient process platform for the reactive extraction of various carboxylic acids from dilute aqueous solutions, but many of the process characteristics of these kinds of processes are not well studied, especially in very long microchannels. In this work, an effort has been made to analyze the mass transfer behavior of very long microchannels during reactive extraction of citric acid from aqueous solutions of different concentrations in a uniform circular, 0.9 mm diameter droplet flow microfluidic contactor using tri-n-octylamine (TOA) in 1-decanol. The above complexation process was confirmed to be a kinetically controlled slow reaction. The devised microfluidic systems delivered higher efficiency than conventional contactors used for liquid-liquid extraction. It was also found that the residence time, TOA concentration, and interfacial area are the important factors that influence the extraction performance. Novel flow schemes developed and presented in this work were successful in manipulating the above influencing factors, which were useful to increase the extraction performance or to reduce the length of the microchannel. The newly developed flow schemes for the flow modification were found to be very efficient in increasing the extraction performance in long microsystems.