A diode laser-based absorption detector is designed for conventional-s
ize 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 mit
oxantrone [signal-to-noise (S/N)= 3; N = root-mean-square (rms) noise]
, an anti-tumor drug, in a biological matrix without any sample cleanu
p. Multipass detection and intensity modulation of the excitation ligh
t did not improve the detection limit. A fiber-optic detector cell, ut
ilizing a gradient-index lens on the light-guiding fiber, was a good a
nd robust alternative for the standard absorption detector cell. Detec
tion limits with the use of the diode laser-based detector are 20-fold
better than those obtained with a commercial absorption detector for
LC.