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present, each at trace levels. T h e pres ence of large molecules and highly conjugated 7r-electronic systems makes fluorometric detection applica ble. T h e asphaltene fraction of coal liquid is injected in 4 0 ^ g total quan tities for reversed phase separation by a 10μ Cis column using a 50:50 acetonitrile:water t o 100% acetonitrile gra dient. By putting the optical-fiber flow cell in series with a commercial UV detector a t 254 nm, one can simul taneously obtain t h e UV absorption, one-photon visible fluorescence, and two-photon excited UV fluorescence in a three-dimensional chromatogram (14). A typical set of three chromatograms is shown in Figure 6. It should be noted t h a t t h e chromatograms are reproducible and that the noise levels in each are insignificant on the corre sponding scales. T h e first observation is t h a t base line resolution is not achieved. This is due to t h e high complexity of these samples a n d t h e inability of the chro matography to properly resolve t h e components. But, t h e three detectors together provide information t h a t is much more useful than each of t h e de tectors individually can provide. T h e
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CIRCLE 2 ON READER SERVICE CARD 1478 A · ANALYTICAL CHEMISTRY, VOL. 5 2 , NO. 13, NOVEMBER 1980
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Retention Time (min) Figure 6. Three-dimensional chromato gram of the asphaltenes: (a) UV absorp tion at 254 n m ; (b) 540-nm fluores cence excited by 488-nm laser; and (c) > 350-nm fluorescence excited by t w o photon absorption of 488-nm laser
