Real-time visualization and recording of laser-induced liquid micro-jet disintegration

Abstract

A powerful technique to study biomolecules and their complexation is pulsed IR-laser induced, liquid beam desorption mass spectrometry. The goal is to transfer biomolecules from their natural envi-ronment softly into the gas phase and analyze (weigh) them with high resolution time-of-flight mass spectrometry. Unfortunately, the evaporation of ionic aggregates of biomolecules from water solution is very difficult due to the large solvation energy and, in general, hot water destroys the biomolecules. Nevertheless, if the process is fast enough charged biomolecules can be desorbed without fragmentation and detected. This can be accomplished by using IR-laser pulses for very rapid heating of a liquid jet containing the biomolecules which causes its disintegration (explosion). However, due to the small liquid jet diameter of 12-15 μm, its high speed of 50-100 m/s, short IR-laser pulses of 8-10 ns and total event duration of a few microseconds only, the microscopic visualization of the jet disintegration was a challenging task. Using a high-speed stroboscopic system running in the back illumination mode high quality video sequences could be recorded. A slow-motion effect has been achieved by sweep of time delay between the pulses of the desorption laser, the light pulse and the camera shutter opening.