A whole-column detection (WCD) system was fabricated using the parts from a typical A4 size optical scanner. Optimum layout of the fluorescence tube, beam condenser and photon transducers from the scanner made an effective devise to examine the dynamic chromatographic separation process. This system was applied in monitoring peak crossover in an ion-pair chromatographic elution. A stage-wise gradient was conducted in eluting a mixture of New Coccine and Carmoisine. Compound New Coccine lagging behind after sample injection moved passing Carmoisine at the column outlet. The complete on-column elution process could be observed directly using this detection system. This inexpensive and rugged WCD system provided a 0.3 mm spatial resolution and a 3.6 ms temporal resolution and was proven to be an adequate device to directly monitor solute retention behavior in the liquid chromatography column.