Immediate observation of matrix assisted laser desorption ionization products in a Fourier transform mass spectrometer

Presented in this dissertation is the instrumentation and methodology for detection of transient matrix assisted laser desorption ionization (MALDI) products using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Simultaneous excitation and detection (SED) is implemented on a 7 T FTICR mass spectrometer to observe ions formed during the first several hundred microseconds of the MALDI event. By matching the capacitance between excite and detect plates of the trapped ion cell, SED enables the detection of ions at the same time the excitation event is occurring. Since detection can now occur even while the ions are being excited, MALDI ion signal is monitored immediately following the desorption event. In addition to fast detection of transient species, the ability of FTICR to detect ion signal as a function of time is exploited in several additional experiments. The velocity of MALDI ions is measured by monitoring the flight time of ions through the trapped ion cell with no trapping voltages applied. This provides a rapid and simple method for obtaining average translational kinetic energy information. The average velocity is measured for several small proteins and is found to be between 224 and 276 m/s. The kinetic energy is found to have a linear dependence on the mass of the analyte. Fast detection combined with experimentally determined ion velocities is used to monitor ion signal as a function of axial position in the mass spectrometer. Cyclotron frequency shifts are found to be consistent with deviations in the magnetic field in a low space charge environment. The ramifications of a high space charge environment early in the MALDI experiment are examined by monitoring cyclotron frequency shifts as a function of time and by pseudo-retarding grid studies. Due to the high space charge environment immediately following the desorption event, shielding of the ion packet is observed, reducing the penetration of the applied electric fields into the ion packet.; A method of broadband SED is introduced for the immediate excitation and detection of multiple MALDI species. By using a short radio frequency (RF) burst, a bandwidth of approximately 1 MHz is achieved. Both analytes in a two component MALDI sample are successfully excited and detected. Broadband SED is utilized for the study of metastable MALDI ions. For the first time, metastable ions are detected in an FTICR mass spectrometer using energetically “hot” matrices such as α-cyanohydroxycinnamic acid (CHCA) and hydroxylphenylazobenzoic acid (HABA). Multiply charged ions are detected, as well as clusters of melittin ions. The lifetime of these metastable ions is calculated and factors influencing their formation are examined.