Matrix fragmentation

The conditions of the FAB process also promote unwanted reactions between analyte and matrix. Even though such processes are not relevant in the majority of FAB measurements, one should be aware of them Besides addition or condensation reactions with matrix fragment ions, [81,82] reduction [83-86] and dehalo-genation [87,88] of the analyte represent the more prominent side-reactions in FAB. Electron transfer to cause the reduction of otherwise doubly charged ions have also been observed. [47]... 

Irradiation of pyridine itself gives Dewar pyridine, observable spectroscopically, which in water is hydrolytically ring-opened to form H2N(CH = CH)2CHO, but in a matrix fragments to cyclobutadiene and HCN. 

Electron density decreases exponentially with distance that suggests that an Additive Fuzzy Density Fragmentation (AFDF) approach can be used for both a fuzzy decomposition and construction of molecular electron densities. The simplest AFDF technique is the Mulliken-Mezey density matrix fragmentation [12,13], that is the basis of both the Molecular Electron Density Loge Assembler (MEDLA) [14-17] and the Adjustable Density Matrix Assembler (ADMA) [18-21] macromolecular quantum chemistry methods. 

In many fuzzy electron density problems the density contributions of the functional groups and other moieties of the molecule X are also considered. In such cases, the membership function pFi (r) defined above is no longer appropriate. An alternative fuzzy set approach, that includes the effects of the electron density contributions of all other functional groups of the molecule, is based on Mezey s additive fuzzy density matrix fragmentation method [20,21],... 

To fabricate extracellular matrix equivalents with soft sugar (polysaccharide) hydrogels interpenetrated with networks of native extracellular matrix fragments and the synthesis of transplantation modules for higher resolution targeting is now a reality. 

Difference in structure between additive and matrix fragments. 

Rost J M 1998 Semiclassical s-matrix theory for atomic fragmentation Phys. Rep. 297 272-344... 

Distance matrix for eight ribose phosphate fragments. 

Bombardment of a liquid surface by a beam of fast atoms (or fast ions) causes continuous desorption of ions that are characteristic of the liquid. Where the liquid is a solution of a sample substance dissolved in a solvent of low volatility (often referred to as a matrix), both positive and negative ions characteristic of the solvent and the sample itself leave the surface. The choice of whether to examine the positive or the negative ions is effected simply by the sign of an electrical potential applied to an extraction plate held above the surface being bombarded. Usually, few fragment ions are observed, and a sample of mass M in a solvent of mass S will give mostly [M + H] (or [M - H] ) and [S -I- H]+ (or [S - H] ) ions. Therefore, the technique is particularly good for measurement of relative molecular mass. 

Collapse Breccia Pipe Deposits. The primary occurrence of coUapse breccia pipe deposits is in circular, vertical pipes fiUed with down-dropped fragments. Uranium is concentrated in the permeable breccia matrix and in the accurate fracture zones enclosing the pipe. An example of... 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

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