Capillary electrophoresis with laser-induced fluorescence detection for natively fluorescent analytes

Laser-induced fluorescence (LIF) detection systems for capillary electropho resis (CE) are nowadays widely available. Many classes of analytes show nat ive fluorescence, but often only upon absorption of short-wavelength UV lig ht. Unfortunately, most CE-LIF systems make use of visible laser lines so t hat they can only be applied to analytes that have been chemically derivati sed with a suitable fluorescent label matching the excitation wavelength. T his paper illustrates how the applicability of Ce-LIF can be broadened to i nclude natively fluorescent analytes by employing either UV laser systems o r multiphoton-excitation. Several pulsed and continuous wave (CW) lasers we re compared in terms of analytical sensitivity and selectivity; in particul ar the CW 275-nm line from an adapted Ar+ laser proved very suitable. For i dentification purposes emission spectra were recorded online. The usefulnes s of such systems in environmental chemistry is shown for amino- and hydrox y-substituted naphthalensulphonates in river water samples. Extra spectral selectivity can be obtained by performing CE-LIF under fluorescence line-na rrowing conditions using a cryogenic interface. The introduction of high-re petition rate, femtosecond Ti:sapphire lasers paved the way for two- and th ree-photon excited LIF detection of a wide array of biologically relevant f luorophores.