COMPARISON OF ULTRAVIOLET-LASER INDUCED AND CONVENTIONAL FLUORESCENCEDETECTION IN CONVENTIONAL-SIZE LIQUID-CHROMATOGRAPHY OF NATIVELY FLUORESCENT ANALYTES
Rj. Vandenesse et al., COMPARISON OF ULTRAVIOLET-LASER INDUCED AND CONVENTIONAL FLUORESCENCEDETECTION IN CONVENTIONAL-SIZE LIQUID-CHROMATOGRAPHY OF NATIVELY FLUORESCENT ANALYTES, Analytica chimica acta, 281(2), 1993, pp. 373-383
The characteristics of laser-induced fluorescence (LIF) detection and
state-of-the-art conventional fluorescence (CF) detection in the UV re
gion below 300 nm in conventional-size column liquid chromatography ar
e compared. An argon-ion laser system is used to provide four laser li
nes, i.e. 257 and 293 nm obtained by frequency-doubling of visible lig
ht and the UV lines at 334 and 352 nm. Light intensities inside the de
tector cell were measured by means of actinometry. Flicker noise, espe
cially important for LIF detection was suppressed by simultaneously mo
nitoring the laser light and ratioing sample and reference signals. On
-line removal of fluorescent impurities in the eluent by means of a pr
ecolumn filled with carbon material resulted in a three-fold reduction
of the background signal for LIF detection with 257-nm excitation. It
is shown that LIF detection at 257 nm is more suitable than LIF at 29
3, 334 and 352 nm, not only for some pharmaceutical compounds that can
only be excited below 300 nm, but also for polyaromatic hydrocarbons
that absorb at wavelengths longer than 300 nm. Compared with CF detect
ion at optimum excitation and emission settings, the detection limits
obtained with the LIF system were improved typically by 5 to 10-fold.