Monitoring of dye adsorption phenomena at a silica glass/water interface with total internal reflection coupled with a thermal lens effect

Thermal lens spectroscopy was combined with total internal reflectance spec troscopy to develop a novel, highly sensitive analytical method that can de tect nonfluorescent as well as fluorescent analytes at surfaces and interfa ces. It was verified that when the total internal reflection method is coup led with thermal lens spectroscopy (TIR-TLS), the thermal lens effect is in duced by only the evanescent wave. The ability of depth profiling was shown . The detection limit of TIR-TLS was at an absorbance of 3.0 x 10(-5) unit for Sudan II acetone solution, which is better than that of attenuated tota l reflection by a factor of hundreds. In addition, the adsorption of acridi ne orange on silanol groups on a glass surface could be monitored directly by TIR-TLS, and the adsorption isotherm agreed well with Langmuir's model. The dependence of surface density of anionic silanol groups on pH was deter mined by TIR-TLS measurements of aqueous acridine orange solutions buffered in the pH range between 2.7 and 11.5.