Photoacoustic Determination of Trace Species Adsorbed on a Single Microparticle

Laser-induced photoacoustic spectroscopy was applied in order to determine trace amounts of iron adsorbed onto the surface of a solid resin Amberlite XAD-2 microparticle of 300 (im in diameter as an oxine (8-quinolinol) complex. The photoacoustic measurements were carried out with a single particle in order to avoid any scattering effects. The signal magnitude depended on the iron concentration, which ranged from 5×10^-3 to 3 mg for one gram of resin. This dependence deviated from linearity as the concentration became larger than 40 µg per gram of resin. The nonlinear behavior was regarded as being a saturation phenomenon resulting from the spatial variation of the optical thickness due to the sample's spherical form. The saturation effect could be eliminated by focusing the incident beam to a size sufficiently small with respect to the particle diameter.