Mechanism of insulin emission in matrix assisted laser ionization

Abstract

In the present paper the emission of intact insulin quasi-molecular ion [M+H] + during laser ablation (MALDI) is studied. It was observed in particular that the insulin TOF molecular peak increases as the laser power increases. The DE-Vestal method for the initial velocity measurements was improved theoretically including the distance (d0) until the free expansion regime can be considered. According to the present analysis, the v0 parameter given by the DE-Vestal method is interpreted as the initial velocity that the desorbed ion would have if no collision occurs in the plasma. The improved method interprets v 0 as the "final" initial velocity, i.e., as the velocity that the desorbed ions have when the plasma free expansion starts and, effectively, collisions no longer occur. The new method allows also the determination of d 0 , the distance to the solid when the free expansion starts. The data fitting shows that the distance (d0) has a linear dependence on the laser's intensity. Extrapolation of these values gives I = 0.69 G W cm −2 as the minimum energy density necessary to produce high density plasma during the insulin ions desorption when using αCHCA matrix.

Simultaneous Mass Analysis of Positive and Negative Ions Using a Dual-Polarity Time-of-Flight Mass Spectrometer

“…Figure presents a sectional view of the simulated electrodes, the potential contours, and the ion trajectories in the region of the duplex MALDI source. The initial kinetic energy of the ions in the + z direction was defined by the empirical results in the literature. − Since no additional focusing device is installed in the field-free drift tubes, the configuration of the duplex source exhibits many unique features for optimizing the transmission efficiency, reducing the beam divergence, and extending the mass working range. According to the predictions for the current configuration, the appropriate initial ionic energy is below 5 eV; for ions of higher initial energy, such as heavy biomolecules, a higher extraction potential is recommended.…”