Concentration Profiling in Layered Liquids Using a Laser Photoacoustic Probe

Abstract

An aluminum-coated Pyrex® glass rod is used both as a photoacoustic probe and as a laser light guide to examine a three-layer solution of carbon tetrachloride, hexane, and an aqueous solution of an efficient chromophore, ferroin. The boundaries of the layers show up clearly on a signal amplitude vs. penetration depth graph. A Beer's law plot of the ferroin solution alone shows that the probe is capable of analytical determinations down to 10⁻⁷ M. Reflections from the cell walls may cause interference in quantitative analysis if the size of the cell is too small. The sensitivity of the probe is compared with that of a typical photoacoustic cell, and it is found that the probe only attenuates the signal amplitude by ∼35%. Finally, it is found that the signal amplitude transmitted by the photoacoustic probe is roughly proportional to its diameter.