Optical detection system bubble.

Sample cell (130) for monitoring the flow of a liquid, the sample cell comprising a cell wall (134) defining a conduit (138), the conduit being provided with a triangular cross section, wherein the wall the cell further defines a base portion (142) and the conduit terminates above the base portion and wherein the base portion of the sample cell is disposed to transmit light between an optical emitter (108 ) and an optical detector (112).