When a light beam travelling through transparent solid is totally reflected from a solid-liquid interface, a part of the beam passes through a thin liquid region bordering on the solid phase. Photoacoustic wave induced in the liquid region at a glass-dye aqueous solution interface by absorption of an intermittent He-Ne laser beam was detected with a piezoelectric transducer. The photoacoustic signal intensity was proportional to a product of the dye concentration and the optical path. The present technique could be applied to observation of a concentration distribution profile of the dye in the solution layer of 200 to 800 nm from the interface at an interval of ca. 50 nm. Detection limit was 4.5×10-3 absorbance unit.
The Japan Society for Analytical Chemistry