Acoustic Trap for Simplified Micro-Sample Handling in Laser Spectroscopy

A tailor-designed acoustic trap has been built and tested as a sample handling device for use in laser spectroscopy. It is based on a piezoelectric vibrator that sets up a standing acoustic wave with several nodes into which liquid or solid samples may be placed and held in a levitated position. The usefulness of such a system to hold samples without the need for sample cells was demonstrated for various experiments involving direct spectroscopic measurements on the suspended sample. Changes in the UV spectrum of bromocresol green dye during a simple pH titration on a drop of the levitated solution were followed by dual dye laser spectrometry. A chemical actinometry spectrochemistry experiment was conducted on Aberchrome 540 fulgide dissolved in DMSO in the levitated state by following changes in the molecular structure of the fulgide by Raman spectroscopy. Finally, crystallization experiments were carried out on droplets and bubbles of tris-(hydroxymethyl)-amino-methane and l-cystein.