Ultra‐sensitive UV detection in micro separation

Most UV detectors used in micro separation techniques today suffer from an enormous loss in sensitivity due to the small cell volume necessary to avoid peak dispersion. Flow cells with volumes between 10‐100 nl are normally constructed of fused silica tubing. With typical path lengths of between 50‐320 μm, a tremendous loss in sensitivity results, consistent with Beer‐Lambert's law. We have successfully constructed an ultrasensitive UV flow cell. Its total volume does not exceed 90 nl and yet its optical path length is nearly 2 cm (20,000 μm). Due to its special design, dead volume is minimized and is comparable to that of a 3 nl capillary flow cell (on‐column). Sensitivity enhancement of 100‐500 times can easily be realized in comparison with on‐column detection. The potential of this ultra‐sensitive UV flow cell in micro separations is illustrated by applications using Capillary LC and Pakked Capillary SFC.