||This thesis proposes mechanisms by which a spiked mobile phase fluorescence detector (SMP-FD) for HPLC is able to detect not only fluorescent compounds, but non-fluorescent chromophoric and non-fluorescent, non-chromophoric compounds as well. This reconfigured fluorescent detector is achieved simply by adding a small quantity of a fluorescent species to the HPLC mobile phase and setting excitation and emission wavelengths to its region of wavelength maxima. The resulting baseline is a steady state fluorescent signal. The objectives of this thesis were to (1) propose mechanisms by which non-fluorescent species are observed as negative peaks, (2) investigate the interference of this background signal on the detection of fluorescent species, and (3) determine optimum conditions for the operation of this detector. Data is presented which suggests that (1) primary and secondary inner filter effects are the cause of negative peaks due to non-fluorescent, chromophoric compounds, (2) changes in the equilibrium distribution of the mobile phase components brought on by the presence of non-fluorescent, non-chromophoric compounds also result in negative peaks. The selection of a mobile phase fluorescent additive is investigated as a means for optimizing a particular analysis. This consists of finding an analyte compatible fluorescent mobile phase additive, wherein spectral overlap with the analyte occurs either in the excitation or emission region or both.