In one aspect, the present invention provides methods, devices, and systems for ensuring that multiple components of a mixture are fully mixed in a continuous flow microfluidic system while ensuring that mixing between segments flowing through the chip is minimized. In some embodiments, the present invention includes mixing fluids in a droplet maintained at the tip of a pipette before the mixture is introduced to the microfluidic device. In another aspect, the present invention provides a pipette tip having a ratio of an outside diameter to an inside diameter that provides sufficient surface area for a droplet comprising up to the entire volume of the liquid to suspend from the pipette tip intact. In yet another aspect, the present invention provides methods, devices, and systems for delivering a reaction mixture to a microfluidic chip comprising a docking receptacle, an access tube and a reservoir.