The aim of this study is the investigation of mass transfer processes in the liquid-liquid system toluene/water. The transfer of different organic solvents and the influence of surfactants on the transfer are investigated. The results are compared with data reported in literature and with ray-tracing computations. In most experimental work concerning mass transfer in liquid-liquid systems a gradient of concentration outside the droplet is neglected. For the experimental determination of such gradients digital holographic interferometry will be introduced.