Some practical aspects of the acceleration-deceleration method for ion kinetic energy focusing in matrix-assisted laser desorption/ionization Fouriertransform ion cyclotron resonance mass spectrometry

A new acceleration-deceleration (AD) method for reducing and focusing ion k inetic energies in matrix-assisted laser desorption/ionization Fourier tran sform ion cyclotron resonance mass spectrometry (MALDI-FTICR) mass spectrom etry has been developed. The aim of the method is to equalize and then redu ce the initial kinetic energy of the MALDI-produced ions, distributed over a broad energy range, by means of delayed acceleration and deceleration of the ions, The focusing of the energy results in a more efficient trapping o f high mass ions and, at the same time, improves the precision of mass meas urements in the ICR trap. The experimental parameters for the acceleration- deceleration ion kinetic energy focusing were predicted by means of the SIM ION 3D software, incorporating both the electric and magnetic fields. The d eceleration of ions both outside and inside the ICR trap was studied. The t heoretical treatment shows that by applying the acceleration-deceleration m ethod it is possible to focus the initially high kinetic energies of 100,00 0 Da ions into a 1 eV range and register their mass spectrum at low trappin g potentials. In order to put the new method into practice, the existing FT ICR mass spectrometer was equipped with a MALDI source inside the magnet. T o compare the acceleration-deceleration method with other methods, the opti mal mass spectrum measurement conditions for several proteomic biopolymers were studied. By means of the acceleration-deceleration method, the MALDI-F TICR mass spectrum of substance P (protonated mass 1347.736 Dal was registe red at 3 x 10(-8) mbar with mass resolution close to 70,000, A resolution o f 45,000 was achieved by the gated trapping method. Bovine insulin B-chain (protonated mass 3494.65 Dal was used to compare the gated trapping method with the deceleration and acceleration-deceleration methods (which also inc lude the gated trapping method as an essential part) at different matrix-to -analyte ratios, The acceleration-deceleration method does not reject high energy ions and has therefore inherently high sensitivity particularly at l ow analyte concentration. Bovine insulin (protonated mass 5732.6 Dal is so far the highest mass ion registered in our spectrometer,It was possible to measure this ion only by the acceleration-deceleration method.