Analysis of concentration-dependencies is key for the quantitative understanding of biological and chemical systems. In experimental tests involving concentration gradients such as inhibitor library screening, the number of data points and the ratio between the stock volume and the volume required in each test determine the quality and efficiency of the information gained. Titerplate assays are currently the most widely used format, even though they require microlitre volumes. Compartmentalization of reactions in pico- to nanolitre water-in-oil droplets in microfluidic devices provides a solution for massive volume reduction. This work addresses the challenge to produce microfluidic-based concentration gradients in a way that every droplet represents one unique reagent combination. We present a simple microcapillary technique able to generate such series of monodisperse water-in-oil droplets (with frequency up to 10 Hz) from a sample presented in an open well, e.g. a titreplate. Time-dependent variation of the well content results in microdroplets that represent time capsules of the composition of the source well.