Versatile Modified Mass Spectrometry

To make the methodology more useful for drug developers, researchers have modified the electrospray ionization component of a high-throughput mass spectrometer so that the sample aerosolization and protein charging processes are separated, which allows the instrument to operate at low voltages with a wide range of solvents.

Electrospray ionization is a technique used in mass spectrometry to overcome the propensity of macromolecules to fragment. In electrospray ionization a liquid is pushed through a very small charged metal capillary by a carrier gas. The liquid contains the substance which is to be studied, the analyte, as well as a large amount of solvent, which is usually much more volatile than the analyte. The charge contained in the capillary transfers to the liquid, which charges the analyte molecule. As like charges repel, the liquid pushes itself out of the capillary and forms a mist or an aerosol of small droplets about 10 µm across, to increase the distance between the similarly charged molecules.

A neutral carrier gas is sometimes used to evaporate the neutral solvent in the small droplets; this in turn brings the charged analyte molecules closer together. The proximity of the molecules becomes unstable, however, and as the similarly charged molecules come closer together, the droplets once again explode. This process repeats itself until the analyte is free of solvent and is a lone ion. The lone ion will then continue along to the mass analyzer.

Investigators at the Georgia Institute of Technology (Atlanta, USA) have developed the AMUSE (array of micromachined ultrasonic electrospray) technology, which they maintain has several advantages over classical electrospray ionization for the separation of proteins. The sample aerosolization and protein charging processes have been separated, giving AMUSE the ability to operate at low voltages with a wide range of solvents. In addition, AMUSE is a nanoscale ion source that can handle much smaller volumes of sample. The description of AMUSE in the May 16, 2005, issue of Applied Physics Letters, holds out the possibility that the expensive electrospray ionization component may be produced cheaply in a disposable format. This would open up new applications for the device in the fields of drug development and clinical diagnostics.




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Georgia Institute of Technology