Capillary electrophoresis with laser-induced fluorescence detection: optical designs and applications

Capillary electrophoresis (CE) has become a very popular analytical technique with applications in various fields including ions, proteins, sugars, and detergents. Fluorescence detection and, more particularly, laser-induced fluorescence detection is recognized to be the best way to overcome the problem of low sensitivity inherent to CE UV detection. Fluorescence detection using an arc lamp as the excitation source, was previously reported. However, only a marginal gain in sensitivity over UV detection was achieved. The main problem is the focusing of a large amount of light from a divergent source onto the tiny detection region of the capillary. The orthogonal arrangement presents two main disadvantages. The one arises from difficulty encountered in correct aligning in the system since two focusing optics are needed: one for excitation and another for emission collection. In a collinear arrangement the excitation radiation is reflected by a dichroic mirror and focused onto the capillary by means of a microscope objective.