Electrophoresis microchip with integrated waveguides for simultaneous native UV fluorescence and absorbance detection

Simultaneous label-free detection of UV absorbance and native UV-excited fluorescence in an electrophoresis microchip is presented. UV transparent integrated waveguides launch light at a wavelength of 254 nm from a mercury lamp along the length of a 1-mm. long detection cell. Transmitted UV light is collected by another waveguide in the opposite end of the detection cell, while visible fluorescence is collected vertically through the lid of the chip.

The background of scattered excitation light is suppressed by detection perpendicular to the excitation, the limited UV transparency of the borosilicate lid and by choosing a PMT insensitive to the excitation light. This way, the need for a fluorescence filter is eliminated. Calibration curves were measured for serotonin, tryptophan, propranolol and acetaminophen, and separations of the four compounds were demonstrated by electrophoresis and MEKC.

All compounds could be detected in the micromolar range by absorbance detection, but fluorescence detection improved detection limits for compounds displaying native UV fluorescence up to ten times. The simultaneous detection also proved useful for the identification of compounds with similar retention times and even enables accurate quantification of co-eluting compounds.