Instrumental advances in time-filtered fluorescence detection

Construction of an improved time filtered fluorescence instrument which utilizes a synchronously pumped, cavity dumped, frequency doubled dye laser for excitation is described. The ultraviolet output increases the number of compounds accessable for analysis. An ultrafast multichannel analyzer is used to collect the data and transfer it to a microcomputer for processing. Advantages over the original time filter instrument which used a single channel analyzer are discussed. Experiments are discribed which show why the alternative method of time resolved detection which involves gated integration is not ideal. The improved instrument uses a software based rather than hardware based time filter window which was utilized by the original instrument. The software evaluates all of the data in order to determine where the window should be placed in time to automatically give the optimum signal to noise ratio for each determination. This advance frees the operator from making the decision on where the window should be placed. A computer model of the instrument is described and the results for a variety of blank types and window optimization schemes are shown. Experimental data are then given which show how the instrument actually performs. Since the eventual goal is to use the instrument for determinations of organic molecules at the 10$\sp{-15}$ Molar level, results of preliminary experiments are described along with the problems of performing analyses at ultrtrace levels. The instrument is capable of a lower limit of detection for $\beta$-Naphthylamine which is only one order of magnitude above the theoretical detection limit for the instrument, assuming a zero blank level. Recommendations for improving the instrument through better laser power stability, laser output power monitoring, a different instrument configuration which allows increased excitation and data collection rates, and increased purification of the water used for the solvent are discussed