Scanning of V, E, and B Fields

There are a variety of possible linked scanning methods, but only those in more frequent use are discussed here. They differ from the linked scanning methods used in triple quadrupole instrument 

Some Methods of Linked Scanning in the First Field-Free Region 

Designation of scan type Set search for precursor or product ions 

V = accelerating voltage at the ion source E = electric-sector voltage B = magnetic-field strength. 

For ions to be focused as they pass through the electric sector, the ratio of V/E must be constant 

There are a variety of possible linked scanning methods, but only those in more frequent use are discussed here. They differ from the linked scanning methods used in triple quadrupole instruments and ion traps in that two of the three fields (V, E, and B) are scanned simultaneously and automatically under computer control. The most common methods are listed in Table 34.1, which also defines the type of scanning with regard to precursor and product ions. 

Linked Scanning and fAetastable Ions in Magnetic-Sector Mass Spectrometry 

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Each of the fields V, E, and B can be varied by itself to examine metastable ions and their connections, but with modern automated techniques it is better to use linked scanning. 

Simultaneous variation of magnetic and electric fields (linked scan methods, conventional or reversed geometry) B/E, constant parent spectrum E /V, simulated MIKE B /E, constant daughter spectrum (B/E) (1 — constant neutral fragment ... 

A FIGURE 12-18 Nuclear pore complex, (a) Nuclear envelopes microdissected from the large nuclei of Xenopus oocytes visualized by field emission in-lens scanning electron microscopy. Top View of the cytoplasmic face reveals octagonal shape of membrane-embedded portion of nuclear pore complexes. Bottom V ew of the nucleoplasmic face shows the nuclear basket that extends from the membrane portion, (b) Cut-away model of the pore complex. [Part (a) from V Doye and E. Elurt, 1997 Curr. Opin. Cell Biol. 9 401 courtesy of M. W. Goldberg and I D. Allen. Part (b) adapted from M. R Rout and J. D. Atchison, 2001, J. Biol. Chem. 276 16593.]... 

C.R. McNeill, H. Frohne, J.L. Holdsworth, J.E. Furst, B.V. King, and P.C. Dastoor, Direct photocurrent mapping of organic solar cells using a near-field scanning optical microscope. 

Linked-field scan at constant B/E. This scan mode is used to obtain a product-ion spectrum on forward- and reverse-geometry inslruments [37]. In this scan, the value of V is fixed and B and E are both scanned while the ratio BIE is held constant. Fragmentation occurs in the first FFR. The mass resolution of the product-ion analysis is much higher selection of the precursor ion is at a lower resolution. 

Linked-field scan at constant B /E. A precursor-ion spectrum of a chosen fragment formed in the first FFR of an EB or BE instrument can be acquired with a linked-field scan, in which the B- and -fields are scanned simultaneously (keeping V fixed) according to the relation B /E = constant Constant-neutral-loss scan. A nentral loss that occurs in the first FFR of both EB and BE instrument can be monitored when the B- and -fields are scanned simultaneously according to the expression B 1 — E )/E = constant (where B is the magnetic field required to transmit m2 and E = E2IE1). 

Figure 10.23. Ferroelectric response of a TGBc phase (compound I2F2BTFO1M7) (a)-(c) Simulated and (d)-(f) experimental X-ray diffraction co-scans of the TGBc phase under the influence of a dc electric field perpendicular to the pitch axis, (a), (d) 0 V (b), (e) 100 V (c), (f) 250 V (from [140]).

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