Observation of particles manipulated by ultrasound in close proximity to a cone-shaped infrared spectroscopy probe

Results obtained with a set-up that enabled us to explore the application of an ultrasonic standing wave to push suspended particles at or into μm distances of the sensing element of an in-line fiber optic probe and subsequently retract them from there are presented. Light micrographs suggested, that the task was successfully accomplished with polystyrene beads suspended in methanol, aggregates were manipulated to and from the cut surface of the truncated, cone-shaped fibre probe tip by changes of the ultrasonic frequency between 1.85 and 1.87 MHz. Feasibility was confirmed by infrared absorption spectra recorded when PTFE particles suspended in tetrahydrofuran were used.