Multi-wavelength light emitting diode array as an excitation source for light emitting diode-induced fluorescence detection in capillary electrophoresis

A multi-wavelength LED array was used as an excitation source for in-column fiber-optic LED-induced fluorescence for CE. The light source consisted of a multi-wavelength LED array consisting of three different LEDs (430, 450 and 480 nm), a focusing lens and a gradient index lens group. The LED beam was collimated and reshaped with the gradient index lens group for coupling the LED light source into a single-mode optical fiber. In addition, the luminance and stability of the LED light source was improved by powering the LED under constant current at enhanced voltages. The benefits of this system were demonstrated by the simultaneous determination of FITC-labeled L-asparagine (Ex/Em 488/520 nm), 4-fluoro-7-nitro-2,1,3-benzoxadiazole-labeled epinephrine (Ex/Em 468/530 nm) and 3-(4-carboxybenzoyl)-quinoline-2-carboxaldehyde-labeled L-leucine (Ex/Em 440/530 nm). Detection limits of L-asparagine, epinephrine and L-leucine were estimated to be 0.8×10-9, 12.0×10-8 and 4.0×10-8 M (S/N=3), respectively. The RSDs (n=6) for migration time and peak area were better than 0.71 and 0.92%, respectively. The performance of the developed multi-wavelength LED excitation source was compared to the use of a single-wavelength LED and found to provide superior sensitivity for the three fluorophores used in this study.