Abstract: A quick-disconnect coupler for a light-transmitting flowcell having in a sight path light-input and light-output windows, respectively, for interposition intermediate a light source and a light detector, respectively, at least in part through a pair of elongated light-transmitting elements, and a support member for the flowcell. There is provided a slip-on flowcell supported on the support member, and a quick-release clamp comprising a pair of jaw members having a pair of corresponding end portions and comprising mounting means for movement of said end portions respectively toward and away from each other and said flowcell windows. The light-transmitting elements have terminals supported in the respective jaw members for alignment with the respective flowcell windows and in contact with said flowcell in the operative positions of the jaws.