Fringe rods

FIGURE 6.7 A 90° ion optic design nsed with curved fringe rods and an off-axis quadrupole mass analyzer (courtesy of Varian Inc.). 

LITs two modes for the mass selective ejection of ions are used either the ions are expelled axially using fringe field effects by applying AC voltages between the rods of the linear trap and the exit lens, or slots are hollowed out in two opposite rods and mass selective radial expulsion of ions is obtained by applying an appropriate AC voltage on these two rods. 

As shown in Figure 2.32, the ions are expelled axially using fringe field effects by applying AC voltages between the rods of the linear trap and the exit lens. 

This instrument can be operated as a normal triple quadrupole with all its scan modes or as a trap in various combinations with the use of the other quadrupoles. If a slow scan rate is used to expel the ions a resolution up to 6000 FWHM can be reached by scanning at 5 Th s 1 using q2 and at 100 Th s 1 using Q3, which is at a lower pressure. As fringe field effects are used, only ions close to the exit lens are expelled. In consequence, mass selective ejection in the axial direction based on this technique is characterized by low ejection efficiency. For instance, an ejection efficiency of less than 20 % is achieved at 1 Th ms-1 scan rate. Different techniques have been proposed to improve the axial ejection efficiency [21], but the most promising technique for mass selective axial ejection is the technique named axial resonant excitation (AREX) [22]. Lenses are introduced between each rod of the quadrupole... 

Using the terminology introduced, we can say that the rods, which are outside the five-dimensional core, form the defects of the globular structure. The interactions of these rods both with each other (because the concentration of rods outside the core is small) and with the rods of the core (because the rods of the fringe do not intersect the core, or intersect it only by the small portion of their length) can be neglected (cf.38 ). Thus,... 

Finally, to determine two still unknown constants, n and n+, it is necessary to find the bondary conditions for the generalized density and to apply these conditions to the density bound between the core and the fringe. We note that the micromotions of the rods inside the five-dimensional core are not hindered by the flexible spacers, since the average distance between the ends of the spacers is much smaller than a. Consequently, there must be a local equilibrium with respect to two elementary acts ... 

This result can be interpreted as follows. The coil-globule transition takes place when the number of rods in the fringe becomes N (the dimensions of the fringe are (a2 + z)1/2). 

From Eqs. (5.33) and (5.34) it is evident that the value of A increases with decreasing temperature (since the fraction of rods in the fringe decreases)... 

White blotches were observed on the kidneys of mice dermally exposed to 7.4 mg chlordane/kg/day, 5 days/week for 20 weeks (Frings and OTousa 1950), but the test sample was probably contaminated with hexachlorocyclopentadiene. A large number of yellow droplets in the renal cortex tubular epithelium and many faintly yellow or colorless, rod-shaped, apparently crystalline structures in the cytoplasm of the cortical tubules were found in all rats that received dermal applications of 217-273 mg/kg/day chlordane in alcohol or cottonseed oil for 1-4 days (Ambrose etal. 1953a). The toxicological significance of these findings is not clear as other studies by any route did not describe similar effects and no control rats were used. 

The equations of motion used to describe the trajectory of an ion in a linear quadmpole (Equation [6.12], Section 6.4.2) are strictly valid only well inside the rod assembly, well removed from the entrance and exit. At each of these ends the ideal quadmpole field (Equation [6.11]) terminates abmptly, but in any real device is affected not only by the RF and DC potentials applied to the rods but also by the potentials applied to nearby ion optical elements (lenses etc.). Moreover, the field lines created by the potentials applied to the rods spill out for some distance outside the theoretical boundaries. These curved fringe fields (Section 6.4.2a) distort the ideal quadmpole field such that the ion motions in the x- and y-directions that are independent of one another in the main quadmpole field (Equation [6.11]) become coupled as a consequence of mixing radial and axial potentials, i.e. the electrical force exerted on an ion in the z-direction can be a function of the time dependent potentials applied in the X- and y-directions (but now curved in three-dimensions), and vice versa. These effects of fringe fields are important in the following discussion. 

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