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Thermal lens spectrometry (1-23) continues to receive widespread attention because of the simplicity, the sensitivity, and the applicability afforded by this technique. Recently, extensive efforts have been directed toward developing the thermal lens method into a practical detector for liquid chromatography (24)(25)(26)(27)(28)(29). These approaches appear to be feasible and promising for several reasons. First, under most chromatographic conditions, the disturbances to thermal lens caused by the flow are usually tolerable (24). Secondly, the coherent laser source, when focused, provides a diffractionlimited beam size that is compatible with the small deadvolume flow cells of the high-performance liquid chromatographs (13). And thirdly, fiied-wavelength UV laser radiation replacing the conventional mercury light source is readily obtainable, for example, from a frequency-doubled Ar+ laser.This source is capable of exciting a good many molecules eluting from the column. A recent study also reveals that a laser source of relatively low power (