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sition of luminescence data as a func tion of multiple excitation and multi ple emission wavelengths was a timeconsuming process. Table I provides a chronology of the improvements in the data acquisition time of luminescence data. Note that a significant decrease in data acquisition time was not real ized until around 1974, and in 1975 when a video fluorometer was devel oped at the Univ. of Washington (23). The video fluorometer's decrease in data acquisition time was due to a novel concept of polychromatic illumi nation coupled with the rapid twodimensional data acquisition capabili ties of an intensified vidicon detector (24). As is often the case with such de velopments, some trade-offs had to be made. In this case, the video fluo rometer is less sensitive than conven tional luminescence instrumentation. However, the sensitivity of the instru mentation could be increased by using the integrating capabilities of the vid icon detector with a concomitant sac rifice in rapid data acquisition. A video fluorometer similar to the one developed at the University of Wash ington has also been described (25, 26). The incorporation of shutters and cryogenic equipment for low-tempera ture operation has also allowed this in strumentation to be used for phospho rescence studies (28,29).
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Lifetime measurements
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CIRCLE 188 ON READER SERVICE CARD 468 A · ANALYTICAL CHEMISTRY, VOL. 57, NO. 3, MARCH 1985
Theory. As mentioned earlier, the luminescence lifetime is another pa rameter that can be used for multiparametric evaluation of the lumines cence information. This can be an especially important property of the luminescing molecules if there is a sig nificant overlap in the excitation and emission bands. In such cases, the life time of the luminophore may be a dis tinguishing factor. The luminescence lifetime is the time required for the luminescence in tensity to decay to 1/e of its initial value (12). Hence, the luminescence intensity can be obtained as a function of monitored wavelength of emission and the observation time after termi nation of the excitation pulse, tit (3) IL —/(Xem.t») A complete mathematical description of the luminescence intensity would require an equation in the form of Equation 2 (4) IL — fCKixtKnniti) Practical considerations determine the approach to acquiring data in the form of Equations 3 and 4. For in stance, two parameters can be fixed and the third one varied (30). Ob viously, the specific instrumentation will determine the necessary acquisi-
