Quadrupole traps

Schlemmer, S. Memann, J. Wellert, S. Gerlich, D., Nondestructive high resolution and absolute mass determination of single charged particles in a three dimensional quadrupole trap, J. Appl. Phys. 2001, 90, 5410 5418... 

This is just what has been done with Ag2. A sputtering source followed by a phase-space compressor chamber provided a beam of cooled negative cluster ions of many sizes. From these, the dimers were selected, accumulated in a quadrupole trap, and photodetached with a femtosecond, titanium-sapphire laser. After photodetachment by a 60-fs pulse, the neutral dimers oscillate, causing corresponding oscillations in the ionization cross section, in turn generating the oscillations that dominate the intensity pattern in Fig. 11. This is a simple phenomenon, yielding in a simple way the... 

Atoms are provided from an rf discharge source, at cryogenic temperatures. After thermalization on the cold cell walls, typically 250 mK, the low field seeking states, c and d (Fig. 1) are attracted to the center of a Ioffe-Pritchard trap, a linear quadrupole trap with a coil at each end to confine the atoms axially. The trapping field is initially about 0.9 T, sufficient to capture atoms with a temperature of about 0.5 K. Once the temperature of the walls is reduced, the temperature of the trapped gas rapidly falls by evaporation, the escaping atoms being trapped on the helium surface. At about 60 mK, the gas becomes isolated from the wall and evaporation ceases. 

Figure 11.56. Block diagram of the ion quadrupole trap apparatus used to detect magnetic resonance and hyperfine spectra of the Hj ion [108].

Keywords. Cold atoms, millimeter waves, terahertz, LIT, finline, quadrupole trap. 

FIG. 4. Strapping pattern for a four-strip cavity designed to produce AC quadrupole trap fields. 

Q-TOF) and quadrupole FTMS (Q-FTMS), significantly increases the specificity and sensitivity of LC-MS and provides for the analysis of highly complex mixtures. This idea has existed in the FTMS community for some time and was recently achieved by the Smith [95] and Marshall Laboratories [96]. The Q-FTMS hybrid allows for greatly enhanced dynamic range via gas-phase selection and concentration of analyte in a quadrupole trap, with subsequent high-resolution MS and MS/MS analysis in FT electromagnetic trap. 

Even slower dissociation rates can be measured by storing ions in an ion trap such as a pulsed ion cyclotron resonance (ICR) cavity (So and Dunbar, 1988) or a quadru-pole ion trap (March et al., 1992), both of which can trap the ions up to several seconds. In the ICR, ions are trapped by a combination of DC electric and magnetic fields, while in the quadrupole trap, they are stored by a combination of RF and DC electric fields. Analysis of either the depleted parent ions or the newly formed product ions is carried out by pulsed extraction of mass selected ions. Thus, the timing with respect to the photodissociation pulse is achieved by delayed ion extraction. The long time limit in this experiment is determined not by the trapping time of the instrument, but by the IR fluorescence rate of ions which is typically 10 to 10 sec > (Dunbar, 1990 Dunbar et al., 1987). 

Moreover, ions could travel much faster in vacuum than in a gas where their velocity is restricted by collisions. For example, ions fly through an evacuated tube of standard TOF MS systems in 20-100 ps, or 1000 times faster than through an IMS drift tube of similar length ( 100 cm). Of course, the feasibility of rapid ion travel in MS does not imply that any MS process must be quick analyses in FTICR, quadrupole trap, and orbitrap systems where ions are stored in circular orbits often last >100 ms, i.e., longer than typical IMS separations. However, the existence of MS techniques placing the usual duration of IMS analyses is (on a logarithmic scale) about halfway between those of MS and condensed-phase methods have crucial implications for practical utility of IMS. 

Ifflander, R. Werth, G. Optical detection of ions confined in a rf quadrupole trap. 

Wells, G.J. Quadrupole Trap Improved Technique for Ion Isolation, US Patent 1993, 5,198,665. 

In scanning instruments (quadrupoles, traps, magnetic) electric or magnetic fields must be varied continuously to obtain spectra... 

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