Analysis of High-Mass Biomolecules Using Electrostatic Fields and Matrix-Assisted Laser Desorption/Ionization in a Fourier Transform Mass Spectrometer

Abstract

A new decelerating technique that places dc potentials on the orthogonal excitation and receiver plates as well as the rear trapping plate (conductance limit) of the source cell of a dual cubic cell has been applied to the standard matrix-assisted laser desorption/ionization Fourier transform mass spectrometry technique. When this five-plate trapping method is applied, high-mass ions with large translational kinetic energies can be trapped efficiently and detected. Using this approach, low-resolution spectra of carbonic anhydrase (MW = 29,000), egg albumin (MW = 45,000), and bovine albumin (MW = 66,000) have been obtained. Because the new decelerating method requires no modification to the existing cell, it is also possible to obtain high-resolution spectra for compounds with masses of ca. 14,000 Da and lower. Utilizing the five-plate trapping method, a bovine insulin spectrum with a resolving power of 20,000 was obtained. It is not yet possible to obtain higher resolution for the higher mass proteins. The reasons for this difficulty are currently being investigated.

Evaluation of different combinations of gated trapping, RF-only mode and trap compensation for in-field MALDI Fourier transform mass spectrometry

“…The potential surface created in the trap for this example is shown in Figure 2. Unlike the surface used by Wilkins and co-workers [6], which was the first shaped retarding field used in FTMS, the surface in Figure 2 requires the higher energy ions that penetrate the furthest into the trap do work in the radial direction as they are decelerated in the z direction whereas this is not the case for the retarding field implemented by Wilkins. The voltages used were held for approximately 60 s after the laser shot.…”

“…Two efforts to improve performance through changes in gated trapping include shaping the trap electric field [6] and exploiting cylindrical traps for improved mass range [7]. A third…”

“…Two efforts to improve performance through changes in gated trapping include shaping the trap electric field [6] and exploiting cylindrical traps for improved mass range [7]. A third approach involves trapping ions with the wide velocity range by using parabolic retarding potentials [8], large retarding potentials [9], a theoretical "two-time constant and a delay" gated trapping strategy [10], and smooth deceleration at the entrance of an open cylindrical trap [11].…”

Trapping of wide range mass-to-charge ions and dependence on matrix amount in internal source MALDI-FTMS

“…A variety of experimental and theoretical approaches have been reported to improve the trapping efficiencies of high mass ions [5,6]. Fourier transform mass spectrometry employing a gated trapping deceleration approach was first applied by Wilkins and coworkers and achieved muchimproved results for low and high mass ions [7][8][9].…”

“…All samples were aerosprayed onto stainless steel probe tips in the same way to ensure homogeneity of the samples. The aerospray method has been described elsewhere [9].…”