Phase transfer and freezing processes investigated on acoustically levitated aqueous droplets

Structure analysis using acoustically levitated droplets

Synchrotron diffraction with a micrometer-sized X-ray beam permits the efficient characterization of micrometer-sized samples, even in time-resolved experiments, which is important because often the amount of sample available is small and/or the sample is expensive. In this context, we will present acoustic levitation as a useful sample handling method for small solid and liquid samples, which are suspended in a gaseous environment (air) by means of a stationary ultrasonic field. A study of agglomeration and crystallization processes in situ was performed by continuously increasing the concentration of the samples by evaporating the solvent. Absorption and contamination processes on the sample container walls were suppressed strongly by this procedure, and parasitic scattering such as that observed when using glass capillaries was also absent. The samples investigated were either dissolved or dispersed in water droplets with diameters in the range of 1 micrometer to 2 millimeters. Initial results from time-resolved synchrotron small- and wide-angle X-ray scattering measurements of ascorbic acid, acetylsalicylic acid, apoferritin, and colloidal gold are presented.

Design and implementation of an efficient acoustically levitated drop reactor for in stillo measurements

We present the details necessary for building an efficient acoustic drop levitator with reduced electrical power consumption and greater drop stability compared to previous designs. The system is optimized so that the levitated drop may be used as a chemical reactor. By introducing a temperature, pressure, and relative humidity sensor for feedback control of a linear actuator for adjusting resonator length, we have built a completely automated system capable of continuous levitation for extended periods of time. The result is a system capable of portable operation and interfacing with a variety of detection instrumentation for in stillo (in drop) measurements.

The dosage of small volumes for chromatographic quantifications using a drop-on-demand dispenser system

A commercially available piezo-driven drop-on-demand dispenser was tested for its suitability for the preparation of analytical calibration standards and in a standard addition approach prior to quantitative ultra performance liquid chromatography (UPLC) analysis of homoserines. The reproducibility of the drop-on-demand dosing system was tested and the verification of the droplet volume was performed by preparing a series of 1.0 mg/L caffeine standard solutions from a 1,000.0 mg/L stock solution and analysis of the concentrations obtained by UPLC. The reproducibility was better than 1% relative standard deviation from measurement to measurement and the highest was 1.6% from day to day. The results were compared with the conventional way of generating standard solutions (pipetting). A gravimetric method and a photography-based method for the determination of the average single droplet volume were compared and found to be in very good agreement. The system was employed for the quantification of N-decanoyl homoserine by standard addition in bacterial culture supernatants containing this analyte. The agreement with conventional quantification techniques was high. The paper shows the feasibility of the approach with advantages in low sample and solvent volume consumption and very good reproducibility and reliability combined with easy usage. Figure Ejected droplet, 60 mus after application of the pulse.