Liquid Chromatography Detectors - The Fluorescence Detector > The Multi Wavelength Fluorescence Detector > Page 62

Fluorescence Detector Program

 

            Time          (seconds)      Wavelength of     Excitation Light    Wavelength of    Emitted Light
                 0            280 nm          340 nm
             220            290 nm          320 nm
             340            250 nm          385 nm
             510            260 nm          420 nm
             720            265 nm          380 nm
           1050            290 nm          430 nm
           1620            300 nm          500 nm

Figure 40. Separation of a Series of Priority Pollutants with Programmed Fluorescence Detection

The separation illustrates the clever use of wavelength programming to obtain the maximum sensitivity. During development both the wavelength of the excitation light and that of the emission light were changed to provide maximum sensitivity for the particular solute.

 

 The detector can provide fluorescence or excitation spectra by arresting the flow of mobile phase when the solute resides in the detecting cell and scanning either the excitation or fluorescent light. (This is the same technique as that used to provide UV spectra with the variable wavelength UV detector). As a consequence, it is possible to obtain excitation spectra at any chosen fluorescent wavelength or fluorescent spectra at any chosen excitation wavelength. Thus, even with relatively poor spectroscopic resolution many hundreds of spectra can be produced, any or all of which (despite many spectra being very similar) can be used to confirm the identify a compound.