Indirect thermo-optical detection for capillary electrophoresis was pr
esented first by combining indirect detection with thermo-optical meth
od. In this detection, methylene blue solution was used as background
electrolyte solution, because it has large molar absorption coefficien
t at 633 nm. This wavelength matches well with that of He-Ne laser(632
.8 nm). The detection was applied to detect amino acids in capillary z
one electrophoresis separation. The detection limit for lysine was 5X1
0(-6) mol/L (S/N=2).