Systems and methods for refractive index detection

A differential refractive index detector comprises a flow cell body comprising a flow cell assembly comprising discrete optically transmissive elements. In one embodiment, the assembly comprises first and second assemblies 214a, 214b having a sample chamber 290 and a reference chamber 214d respectively, wherein the two assemblies are joined, possibly by a fastener, screw, or clamp. There may be transparent windows 260a, 260b, 260c with edge seals or gaskets preventing fluidic leakage from the chambers and separating the chambers fluidically from each other. Window 260c may be adjacent to a main joint including an O-ring seal 282. In another embodiment, the discrete optically transmissive elements include a sample chamber 290 and a reference chamber 214d, and a cross-sectional profile of at least one of the chambers, taken perpendicular to a flow axis, includes at least one curved portion. The chambers may each be formed by a circular or elliptical bore through a long axis of the flow cell body.