Diode laser-based absorption detector for conventional-size liquid chromatography

A diode laser-based absorption detector is designed for conventional-size liquid chromatography (LC). To this end, various detection setups and individual components have been evaluated. A ratioing system using a 10-mW 670-nm diode laser allowed the detection of 6 x 10(-10) M mitoxantrone [signal-to-noise (S/N)= 3; N = root-mean-square (rms) noise], an anti-tumor drug, in a biological matrix without any sample cleanup. Multipass detection and intensity modulation of the excitation light did not improve the detection limit. A fiber-optic detector cell, utilizing a gradient-index lens on the light-guiding fiber, was a good and robust alternative for the standard absorption detector cell. Detection limits with the use of the diode laser-based detector are 20-fold better than those obtained with a commercial absorption detector for LC.