Effect of the position of the laser beam focal point on a capillary flow-through cell on the signal-to-noise ratio for a fluorimetric detector in capillary column liquid chromatography

Abstract

The use of a high-sensitivity laser-induced fluorescence detector with a capillary flow-through cell (100 μm I.D.) in capillary column liquid chromatography was studied. To reduce the background noise from scattering of the laser light from the cell walls by reflection and refraction, the geometric position of the focal point of the laser beam on the capillary cell is very important. By moving the focusing lens of the laser beam, the best position of the laser on the capillary cell was examined. The use of a video camera was also helpful in setting the laser beam on the capillary cell. With the optimum geometric arrangement, 1.3 fmol of the 4-bromomethyl-7-methoxycoumarine derivative of caproid acid ( k′ = 3) was detected at a signal-to-noise ratio of 5.