Recent improvements in and analytical applications of advanced ion trap technology

Burinsky

2008

101

Mass spectrometers that use different types of analyzers for the first and second stages of mass analysis in tandem mass spectrometry (MS/MS) experiments are often referred to as "hybrid" mass spectrometers. The general goal in the design of a hybrid instrument is to combine different performance characteristics offered by various types of analyzers into one mass spectrometer. These performance characteristics may include mass resolving power, the ion kinetic energy for collision-induced dissociation, and speed of analysis. This paper provides a review of the development of hybrid instruments over the last 30 years for analytical applications. (J Am Soc Mass Spectrom 2008, 19, 161-172) © 2008 American Society for Mass Spectrometry T andem mass spectrometry (MS/MS), in a very generic description, is a process in which an ion formed in an ion source is mass-selected in the first stage of analysis, reacted, and then the charged products from the reaction are analyzed in the second stage of analysis. The type and quality of data that is obtained can vary greatly depending upon the type of analyzer used in the first and second stages of analysis, and the type of reaction performed between the stages of analysis. The reactions that can be done also can depend upon the type of analyzer. Over the years there have been a variety of means developed to measure the mass-to-charge ratio of gas-phase ions. The most common methods involve: dispersion based on ion momentum or kinetic energy (magnetic and electric sector instruments); separation in time based on ion velocity (time-of-flight); transmission through an electrodynamic field (quadrupole mass filter); and periodic motion in a magnetic or electrodynamic field (ion traps). There are differences in the experimental parameters associated with these various analysis methods that are pertinent to the MS/MS experiment. Some parameters are obvious, typically related to the performance of the mass analyzer while others are more subtle, related to the reactions/chemistry occurring between the stages of analysis. Many times these different parameters are used to categorize MS/MS experiments.One parameter is the ion kinetic energy. Sector and time-of-flight (TOF) instruments typically operate at "high" ion kinetic energies (5-20 keV), whereas "low" ion kinetic energies (Ͻ50 eV) are typical in quadrupole mass filters and ion traps. The ion kinetic energy is an important parameter in MS/MS experiments because the most common reaction involves colliding the ion of interest with a target gas atom or molecule. When performing ion-neutral collision experiments, the possible reactions that can be accessed (e.g., collisioninduced dissociation, collisional cooling, charge permutation, ion/molecule reaction) depends upon the ion kinetic energy. The appearance of the MS/MS spectrum can change drastically as a function of the collision (ion kinetic) energy. A related factor that is equally important, but often not considered, is the time frame of the experiment, that is, the elapsed time bet...

Section: Beam-trap Hybrid Instrumentsmentioning

confidence: 99%

Hybrid mass spectrometers for tandem mass spectrometry

Burinsky

2008

101

“…The sensitivity of a quadrupole ion trap mass spectrometer is optimized with a bath gas pressure around 1.0 ϫ 10 Ϫ3 Torr. Bath gas collisions reduce the kinetic energy of trapped ions and minimize the size of the ion cloud [12]. However, collisions also remove internal energy gained from IR absorption, necessitating longer periods of irradiation for dissociation and decreasing fragmentation efficiency [13],…”

mentioning

confidence: 99%

Improving IRMPD in a quadrupole ion trap

Newsome

2009

A focused laser is used to make infrared multiphoton photodissociation (IRMPD) more efficient in a quadrupole ion trap mass spectrometer. Efficient (up to 100%) dissociation at the standard operating pressure of 1 ϫ 10 Ϫ3 Torr can be achieved without any supplemental ion activation and with shorter irradiation times. The axial amplitudes of trapped ion clouds are measured using laser tomography. Laser flux on the ion cloud is increased six times by focusing the laser so that the beam waist approximates the ion cloud size. Unmodified peptide ions from 200 Da to 3 kDa are completely dissociated in 2.5-10 ms at a bath gas pressure of 3.3 ϫ 10 Ϫ4 Torr and in 3-25 ms at 1.0 ϫ 10 Ϫ3 Torr. Sequential dissociation of product ions is increased by focusing the laser and by operating at an increased bath gas pressure to minimize the size of the ion cloud. nfrared multiphoton photodissociation (IRMPD) has been used for tandem mass spectrometry in a quadrupole ion trap mass spectrometer [1][2][3][4][5][6][7] and a Fourier transform ion cyclotron resonance mass spectrometer [8 -11] as an alternative to collision-induced dissociation (CID). Only one m/z ion is selected for excitation in conventional CID, limiting sequential dissociation of product ions into smaller mass product ions. Conversely, in IRMPD all parent and product ions are irradiated simultaneously with a collimated, IR laser providing the capability to generate abundant small mass product ions. IRMPD is typically performed in a quadrupole ion trap mass spectrometer at a smaller low mass cut-off (LMCO) than CID, allowing the observation of a broader m/z range of product ions [2,4], and a higher MS/MS efficiency,where E MS/MS is MS/MS efficiency, F i is the abundance of each product ion, and P 0 is the initial abundance of the parent ion before irradiation. IRMPD is performed in a Fourier transform ion cyclotron resonance mass spectrometer to eliminate the need for a CID target gas to be leaked into and pumped out of the ICR cell [10,11]. The sensitivity of a quadrupole ion trap mass spectrometer is optimized with a bath gas pressure around 1.0 ϫ 10 Ϫ3 Torr. Bath gas collisions reduce the kinetic energy of trapped ions and minimize the size of the ion cloud [12]. However, collisions also remove internal energy gained from IR absorption, necessitating longer periods of irradiation for dissociation and decreasing fragmentation efficiency [13],where E F is fragmentation efficiency, F i is the abundance of each product ion, and P is the abundance of the parent ion remaining after irradiation. IRMPD in a quadrupole ion trap mass spectrometer often is performed at 1 ϫ 10 Ϫ5 to 3 ϫ 10 Ϫ4 Torr to decrease collisional cooling of parent ion internal energy [2-7], [13] and achieve dissociation with shorter irradiation times. However, this reduced bath gas pressure is less effective for trapping ions during injection and reduces sensitivity.Several methods have been developed to increase IRMPD fragmentation efficiency by combining IRMPD with another form of ion activation an...

“…The theoretical calculation of ion internal energy in a QITMS is a complex quantum chemical calculation in which many factors must be considered, such as the kinetic energy of the ion, the vibrational energy states of the ion, and the probability of energy-transfer from one state to another [8]. These considerations are complicated by the necessary presence of helium (He) bath gas at ϳ1.3 ϫ 10 Ϫ3 mbar in the QITMS to improve sensitivity and mass resolution [9]. Other types of mass spectrometers typically operate at pressures low enough to ensure that the flight path of the ion is shorter than the mean free path between collisions with background neutral gas.…”

mentioning

confidence: 99%

On the time scale of internal energy relaxation of AP-MALDI and nano-ESI Ions in a quadrupole ion trap

Remes

2009

Recently reported results (Konn et al. [14]) on the collisional cooling of atmospheric pressure matrix assisted laser desorption ionization (AP-MALDI) and nano-electrospray ionization (nano-ESI) generated ions in a quadrupole ion trap mass spectrometer (QITMS) are inconsistent with measured collisional cooling rates. The work reported here presents a re-examination of those previous results. Collision induced dissociation (CID) has been used to probe various properties of ions contained in a QITMS. It is shown experimentally that when trapping large numbers of ions, an effective dc trapping voltage is induced that varies with changes in the size of the ion cloud. A decrease in the resonant frequency for maximum CID efficiency is observed as the cool time between parent ion isolation and CID is increased. Ion trajectories in a QITMS are simulated to demonstrate how ion density changes over the course of parent ion isolation. The effect of space charge on ion motion is simulated, and Fourier transformations of ion axial motion plus simple calculations corroborate the experimentally observed transient frequency shifts. The relative stability of ions formed by AP-MALDI and nano-ESI is compared under low charge density conditions. These data show that the ions have reached equilibrium internal energy and, thus, that differences in dissociation onsets and "50% fragmentation efficiency points" between the ionization mechanisms are due to the formation of distinct ion conformations as previously shown in reference [28] A n understanding of ion internal energy is of primary interest to researchers studying the structures of gas-phase ions. How fast an ion will dissociate, which mechanisms will be involved, and how many products will be observed all have a large dependence on the amount of internal energy in the ion and the experimental time window for dissociation [1][2][3][4]. If the internal energy of an ion is distributed statistically among its bonds, RRKM theory can determine the dissociation kinetics of the various dissociation pathways, and mass spectra or tandem mass spectra (MS/MS) could be predicted [5][6][7]. MS/MS spectra are related to ion structure on a fundamental level because the vibrational bond frequencies, the ground state energy, and the critical energy of dissociation are all determined on some level by the three dimensional conformation of the ion.Because MS/MS spectra have a dependence on structure and internal energy, it is important to understand the various factors that determine ion internal energy and how its magnitude might change over the course of an experiment. A typical experiment using a quadrupole ion trap mass spectrometer (QITMS) lasts several hundred ms, during which time a large number of variables can affect an ion population's distribution of internal energy. The theoretical calculation of ion internal energy in a QITMS is a complex quantum chemical calculation in which many factors must be considered, such as the kinetic energy of the ion, the vibrational energy states of the io...