Lamp-based wavelength-resolved fluorescence detection for protein capillary electrophoresis: setup and detector...

A lamp-based fluorescence detection (Flu) system for CE was extended with a wavelength-resolved (WR) detector to allow recording of full protein emission spectra. WRFlu was achieved using a fluorescence cell that employs optical fibres to lead excitation light from a Xe-Hg lamp to the capillary window and protein fluorescence emission to a spectrograph equipped with a CCD. A 280 nm band pass filter etc. together with a 300 nm short pass cut-off filter was used for excitation. A capillary cartridge was modified to hold the detection cell in a commercial CE instrument enabling WRFlu in routine CE. The performance of the WRFlu detection was evaluated and optimised using lysozyme as model protein. Based on reference spectral data, a signal-intensity adjustment was introduced to correct for transmission losses in the detector optics that occurred for lower protein emission wavelengths. CE-WRFlu of lysozyme was performed using BGEs of 50 mM sodium phosphate (pH 6.5 or 3.0) and a charged-polymer coated capillary. Using the 3-D data set, signal averaging over time and emission-wavelength intervals was carried out to improve the S/N of emission spectra and electropherograms. The detection limit for lysozyme was 21 nM, providing sufficient sensitivity to obtain spectral information on protein impurities.