High-sensitivity chromatographic detector incorporating three-dimensional charge coupled device fluorimetry

This article describes a detector for liquid chromatography that provides three-dimensional, excitation–emission-intensity data of fluorescent compounds. The instrument achieves multi-wavelength excitation by employing a polychromator that disperses radiation along the vertical portion of a quartz capillary flow cell. The ensuing sample fluorescence is collected in the horizontal plane and dispersed using an emission polychromator to form a focused two-dimensional excitation–emission image at a charge coupled device (CCD) pixel array. Each vertical pixel equates to a narrowly defined excitation wavelength band, whilst horizontal pixels equate to corresponding emission wavelengths, with the intensity of light encroaching onto the CCD pixel elements providing the third-dimensional variable in the measurement. It is shown that the extreme sensitivity of CCD detection coupled to the dual polychromator arrangement makes possible the collection of fluorescence excitation–emission-intensity data of polycyclic aromatic hydrocarbons in a flow stream in less than 0.05 s with nanogram per millilitre limits of detection.