An apparatus to control and automate the formation of continuous density gradients

A common problem associated with making a continuous density gradient is the unwanted mixing of liquids as the gradient solution is being delivered from the gradient mixer to the centrifuge tube. We show that by using a Styrofoam float on a thin drawn-out glass pipette, liquids from the gradient mixer will flow down the outside surface of the glass fiber and contact the float, after which the liquid spreads across the gradient surface without unwanted mixing. As the liquid in the tube rises, the float rises up the glass fiber, thereby allowing the creation of gradients without the need to monitor the process.