Linked-field scans

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). 

Linked-field scan at constant B E. To obtain a precnrsor-ion spectrum on a BE instrument, B is scanned upward and E downward, holding the product B E constant precursor-ion selection and fragmentation occur in the second FFR (i.e., in front of the electric sector). 

Mass-Analyzed Ion Kinetic Energy Spectrometry. Tetrahedron 37, 2625 (1981). Gaskell, S. j., a. W. Pike, and D. S. Millington The Fragmentation of Stereoisomeric Androstanediol r-Butyldimethylsilyl Ethers. A study of Linked-Field Scanning. Biomed. Mass Spectrom. 6, 78 (1979). 

Desiderio, D. M., and I. Katakuse Fast Atom Bombardment-Collision Activated Dissociation-Linked Field Scanning Mass Spectrometry of the Neuropeptide Substance P. Analyt. Biochem. 129, 425 (1983). 

Millington, D.S. Smith, J.A. Fragmentation Patterns by Fast Linked Electric and Magnetic Field Scanning. Org. Mass Spectrom. 1911,12, 264-265. 

Different types of linked magnetic sector field (B) and electric sector field ( ) scans can yield different information from transitions in the first field-free region, and from the penultimate field-free region... 

The study of metastable ions concerns substances that have been ionized by electrons and have undergone fragmentation. The stable molecular ions that are formed by soft ionization methods (chemical ionization. Cl field ionization, FI) need a boost of extra energy to make them fragment, but in such cases other methods of investigation than linked scanning are generally used. 

Scanning for metastable ions requires adjustment of electric and magnetic fields which can be adjusted individually or in conjunction with each other. If two fields are automatically adjusted at the same time, it is known as linked scanning. It is important to remember that metastable ions are not the product ions m2 but are the ions undergoing fragmentation (precursor ions mj). 

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. 

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

In an EW- of a B/E-linked scan using an electric/magnetic-sector instrument, a precursor ion is selected. In this case it is m, which might be a molecular ion but equally could be any fragment ion. All product ions (mj, m3, m4) from decomposition of m, in the first field-free region between the ion source and the ion collector are found, thereby giving connections mpm, m -m3, m -m4. 

By adjusting magnetic and electric fields in the ion optics (see Chapters 33 and 34 on linked scanning), metastable ions can be investigated. 

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. 

Linked scan. A scan, in an instrument with two or more analyzers, in which two or more of the analyzer fields are scanned simultaneously to preserve a predetermined relationship between parameters that characterize these fields. Often these parameters are the field strengths, but they can be the frequencies in the case of analyzers that use alternating fields. 

B. a term meaning the strength of a magnetic field, often used to refer to a magnetic field or sector B/E. a method of linked scanning for metastable ions, which uses combined m netic and electric fields B /E. a method of linked scanning for metastable ions, which uses combined magnetic and electric fields CAD. collisionally activated decomposition... 

EW. a method of linked scanning for metastable ions, which uses electric fields (see V)... 

Linked scanning A series of techniques in which the electrostatic analyser voltage and magnetic field strength of a double-focusing mass spectrometer are scanned to obtain MS-MS spectra. 

J. Shen and A. S. Al-Saeed. Study of oil field chemicals by combined field desorption/collision-activated dissociation mass spectrometry via linked scan. Ana/y Chem, 62(2) 116-120, 1990. 

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