Paul traps

Another approach to mass analysis is based on stable ion trajectories in quadnipole fields. The two most prominent members of this family of mass spectrometers are the quadnipole mass filter and the quadnipole ion trap. Quadnipole mass filters are one of the most connnon mass spectrometers, being extensively used as detectors in analytical instnunents, especially gas clnomatographs. The quadnipole ion trap (which also goes by the name quadnipole ion store, QUISTOR , Paul trap, or just ion trap) is fairly new to the physical chemistry laboratory. Its early development was due to its use as an inexpensive alternative to tandem magnetic sector and quadnipole filter instnunents for analytical analysis. It has, however, staned to be used more in die chemical physics and physical chemistry domains, and so it will be described in some detail in this section. 

Principle. The cylindrical quadrupole ion trap is based on the same principle as the quadrupole mass filter, but the geometry is different (Fig. 2.16). The cylindrical QIT, or Paul trap, was developed almost simultaneously with the quadrupole mass filter [232, 233]. Recently, a variant of the theme has emerged, the linear quadrupole ion trap [236], which is a device built like a quadrupole mass filter with extra trapping end electrodes for the axial direction. Under stable conditions, ions moving around inside such traps will ideally continue to do that forever. 

Paul traps, 15 662 Pauson-Khand reaction, 16 72 Pavements, insulated, 23 405 Paving, 19 494 epoxy, 10 453 Payback time (PT), 9 546 Paylean, 13 2... 

AUieit, R. Kleinadam, S. Vedel, F. Vedel, M. Werth, G. Higher Order Non-Linear Resonances in a Paul Trap. Int. J. Mass Spectrom. Ion Proc. 1996, 154, 155-169. 

Makarov, A.A. Resonance Ejection From the Paul Trap A Theoretical Treatment Incorporating a Weak Octa-pole Field. Anal. Chem. 1996, 68, 4257-4263. 

Storage has mainly been achieved in four types of traps (11 the radio frequency or Paul trap (2) the Penning trap (3) the Kingdon electrostatic trap and (4) the magnetostatic (magnetic bottle) trap. The principles, advanlages, and disadvantages of these traps are detailed by DJ. Wineland (Science, 226, 395-400, Oct. 26, 1984). 

The ion is trapped in a quadrupole radiofrequency trap that is a geometrical variant of the original Paul trap and basically consists of only a ring electrode... 

We end this section with an example for an unexpected constant of the motion (Bliimel et al. (1989a)) that was recently discovered to play a role in the dynamics of a Hamiltonian that approximately describes two charged particles in a Paul trap (Paul et al. (1958), Paul (1990)). 

The Paul trap is a device of considerable importance for high-resolution laser spectroscopy. Moreover, the Paul trap has been proposed as the centrepiece of a new generation of ultra-stable atomic clocks (see, e.g., Itano et al. (1983), Wineland et al. (1984)). Related trap designs have very recently come into prominence from their use in first observation of gaseous Bose-Einstein condensation (Anderson et al. (1995), Collins (1995)). 

In appropriate units, an approximate Hamiltonian of two ions in a Paul trap is given by... 

Bliimel, R. (1993a). On the integrability of the two-ion Paul trap in the pseudo potential approximation, Phys. Lett. A174, 174-175. 

Bliimel, R., Kappler, C., Quint, W. and Walther, H. (1989a). Chaos and order of laser-cooled ions in a Paul trap, Phys. Rev. A40, 808-823. 

Howard, J.E. and Farrelly, D. (1993). Integrability of the Paul trap and generalized van der Waals Hamiltonians, Phys. Lett. A178, 62-72. 

Moore, M. and Bliimel, R. (1993). Quantum manifestations of order and chaos in the Paul trap, Phys. Rev. A48, 3082-3091. 

The most direct approach to the geometric structures of molecules and also of clusters in the gas phase are diffraction methods, in particular the diffraction of an electron beam. Since an adequate cluster flux for such electron diffraction experiments has been so far only possible, if the full source output beam was sampled, the uncertainties in cluster size (no mass-selection) and internal energy prevent an unambiguous interpretation of electron diffraction patterns [138-145]. In a new development, a technique has been recently reported that relies upon an rf-Paul trap [146] to take advantage of the current... 

The three-dimensional quadupole field ion trap - or Paul trap is a three-electrode device [see Figure 4.5(b)]. Ions are injected into the device and collected in packets from an ESI or MALDI source. The ion trap analyzer is capable of MS, MS" (MS = MS-MS-MS) and high-resolution scans (R = 20,000). The ion packets enter through an entrance-end cap and are analyzed by scanning the RF amplitude of the ring electrode. The ions are resonated sequentially from low to high m/z and are ejected from the ion trap through the exit-end cap electrode to a detector. Unlike the triple quadrupole (QqQ) mass spectrometer discussed previously, the ion trap performs tandem mass spectrometry (MS-MS) scan modes in the same analyzer. 

The ion trap is often called the Paul trap after the Nobel Prize winner, Dr. Wolfgang Paul, who invented the device in the 1950s. 

In the experiments we discuss here, a single Be ion was stored in a conventional Paul trap [1-3] where the ion s confinement is characterized by secular oscillation fi-equencies ((0 0), 0j)/2it (11, 19, 29) MHz along the three principal axes of the trap [14]. The future goal of the work will be able to extend these experiments to the case of multiple ions in a linear trap (Fig. 1). 

The trap used for the present experiment was a modified Paul-trap, called an endcap-trap (17) (see Fig. 1) which produces good confinement of the trapped ion. Therefore, the number of sidebands in the fluorescence spectrum, caused by the oscillatory motion of the laser cooled ion in the pseudopotential of the trap. 

The Paul trap is housed in a central climate chamber which can be cooled down to the temperature of liquid nitrogen. The pressure and composition of the background gas in this chamber can be controlled by a gas mixing and inlet system and is usually adapted to stratospheric conditions. This chamber is suspended inside an insulation chamber which is kept at high vacuum. This chamber is equipped with a quadrupole mass spectrometer to analyze the chemical composition of the atmosphere, which leaks from the central chamber through a small pinhole. This system of vacuum chambers is connected to a standard time-of-flight mass spectrometer by means of a droplet translator. This is a cold finger which can be used to... 

FIGURE 2.7 Instantaneous electric potential in electrodynamic (Paul) trap. Insert Temporal variation of the potential. For a colour reproduction of this figure see the colour plate section, near the end of this book. 

FIGURE 2.7 Instantaneous electric potential in electrodynamic (Paul) trap. Insert Temporal variation of the potential. 

Ion-trap methods include Fourier transform ion cyclotron resonance MS (FTICR-MS) and quadrupole ion traps (QIT or Paul traps). In these methods, ions are produced in or transferred into a region with appropriate geometry walls and some combination of magnetic fields, DC potentials, and RF potentials that confine the ions on the timescale of seconds to days. FTICR-MS has been particularly popular for the study of organometallic ions in the gas phase. In FTICR-MS, the ions are confined by a magnetic field that constrains the ions to the center of the cell. 

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