Electrospray-assisted laser desorption ionization (ELDI) is a technique which combines laser desorption with subsequent electrospray ionization. It is useful for directly detecting small and large molecules in solid or liquid samples under ambient conditions. In this paper, the detection of the protein molecules desorbed on a dry protein spot by using pulse laser energies of up to 300 microJ was demonstrated. The influences of organic and inorganic matrices, the laser energy, the laser wavelength, and the sample plate material on desorption of protein molecules from sample plates were discussed. In addition, the effects of the composition of the electrospray solution on the ionization of the desorbed protein molecules were studied.

Electrospray laser desorption ionization mass spectrometry (ELDI/MS), an ambient mass spectrometric technique that combines laser desorption with postionization via electrospray, was developed to rapidly characterize analytes ranging from small organic to large biomolecules. The technique requires essentially no sample pretreatment. The analytes are desorbed through pulsed laser irradiation in the absences of organic matrices like those used in matrix-assisted laser desorption ionization (MALDI). The desorbed molecules subsequently enter an electrospray plume and are postionized through reactions with charged solvent species such as protons, cluster solvent ions, and charged droplets (also termed as species produced from an acidic methanol electrospray solution). This chapter provides a full-scale review of the ELDI technique including its development, underlying principles of operation, ionization mechanism, unique features, related techniques, and applications.