NEAR-INFRARED LASER-INDUCED FLUORESCENCE DETECTION IN COLUMN LIQUID-CHROMATOGRAPHY - A COMPARISON OF VARIOUS LASERS AND DETECTION SYSTEMS .1. CONTINUOUS-WAVE LASERS

Several lasers, i.e. HeNe lasers, diode lasers and an argon-ion-dye laser combination, are compared as excitation sources for near-infrared laser-induced fluorescence detection in column liquid chromatography. Using a model gradient liquid chromatography system, detection limits for disulphonated aluminum phthalocyanine (AlPcS2) were compared after optimization of the signal processing scheme for each laser. The best detection limit (1.5 . 10(-13) M) was obtained for the argon-ion-dye laser combination, applying ratioing of emission and excitation light to reduce flicker noise. Utilizing diode laser excitation there is;no need far ratioing so that emission collection can be improved and a detection limit similar to that obtained with the argon-ion laser can be achieved. As this device is very cheap, the diode laser is the best choice for most applications. If tunability over a large wavelength region is essential, the argon-ion-dye laser combination is a good but expensive alternative.