Abstract: A capillary flowcell of this invention comprises a holding means including an optical axis, the optical axis being defined by, in sequential order, (a) a first (entrance) aperture, (b) a first lens, (c) a capillary tube having its long axis centered across the optical axis, and (d) a second lens. The first lens focuses electromagnetic radiation from the entrance aperture passes through the inner diameter of the capillary tube, thus maximizing the signal generated by the analyte within the capillary tube. The second lens focuses electromagnetic radiation which has passed through the capillary tube. Methods and apparatus pertaining to the flowcell are given.

Abstract: A fluorescence flow cell having a capillary through which a sample fluid is moved, an optical source that directs an exposing beam of light through the sample fluid, a collector that collects fluorescent light from the exposed region of the sample and directs such collected light to a detector. A beam blocker prevents light that is scattered by the capillary walls from reaching the detector, thereby improving the signal-to-noise ratio of the system. The beam blocker also has a pair of legs that prevent the sample fluid from being exposed by either the exposing light or the collected light outside of the exposing region. The structure of the components enables the various components to be quickly and accurately assembled and enables easy replacement of the capillary.