Abstract

The use of lasers for detection in liquid chromatography (LC) has been gaining in popularity. The reason is that unique properties of the laser beam fit well with many of the requirements in LC. Fluorescence is one of the widely used laser-based techniques. However, one is often limited by the availability of a fluorophore, the availability of the appropriate laser wavelength, and the poor intensity stability of lasers. A possible solution is to use indirect fluorometry. Because there is always a solvent present in LC, one can include a fluorescent probe in the solvent. There is then a large background fluorescence in the optical region at all times. When analytes elute from the chromatographic system, they can displace the probe molecules to cause a lower fluorescence signal. This then allows fluorometry to be used to detect non-fluorescing species. Since the choice of the fluorophore is governed by some broad guidelines, a convenient laser wavelength can be used. The stability of the laser intensity is critical to detection at low concentrations. Good stability can be achieved in a double-beam arrangement with modulation at high frequencies. To enhance detection, we make use of the competition between the probe molecule and the analyte either by ion exchange or by adsorption on the LC column. Good mass detectability is possible when microbore or open capillary LC columns are used.

© 1987 Optical Society of America