In this paper, the extraction of vanillin dissolved in water with a suitable organic phase using microstructured devices made of PDMS is discussed. Two flow patterns, segmented and stratified flow, were compared. LIF and mu-PIV measurements showed a laminar profile for stratified flow; whereas for segmented flow, vortices in the slug end were detected. Additionally, for the stratified flow regime, the influence of the channel width and therefore the surface-to-volume ratio was investigated. A decrease of the channel cross-sectional area results in a significant enhancement of mass transfer for the stratified flow regime. A further increase in mass transfer was obtained using segmented flow instead of stratified flow. However, stratified flow may be favored due to the ease of implementation of phase separation on the chip.