Matrix crystallization

A third possibility is that partial separation will occur on the MALDI target, such as during matrix crystallization,96 which can be distinguished by rastering the laser beam. 

On the basis of the concept described above, we propose a model for the homogeneous crystallization mechanism of one component polymers, which is schematically shown in Fig. 31. When the crystallization temperature is in the coexistence region above the binodal temperature Tb, crystal nucleation occurs directly from the melt, which is the well-known mechanism of polymer crystal nucleation. However, the rate of crystallization from the coexistence region is considered to be extremely slow, resulting in single crystals in the melt matrix. Crystallization at a greater rate always involves phase separation the quench below Tb causes phase separations. The most popular case... 

Figure 21.6 Time-lapse observation of synaptic acid crystal formation. The spray-droplet method forms very fine crystals inside and outside of the matrix drop (a-d), so that finer and more homogeneous crystals are generated (d) than those obtained by the droplet method (e-h). Observation with a scanning electron microscope of matrix crystals with the spray-droplet (i) and droplet methods (j). Reprinted with permission from Sugiura et al.7... 

K. Is the Incorporation of Analytes into Matrix Crystals a Prerequisite for MALDI-MS A Study of Five Positional Isomers of Dihydroxybenzoic Acid. Int. J. Mass Spectrom. 1999,185/186/187, 859-870. 

Other interferences which may occur in flame AAS are ionization of the analyte, formation of a thermally stable compound e.g., a refractory oxide or spectral overlap (very rare). Non-flame atomizers are subject to formation of refractory oxides or stable carbides, and to physical phenomena such as occlusion of the analyte in the matrix crystals. Depending on the atomizer size and shape, other phenomena such as gas phase reactions and dimerization have been reported. 

Defect clustering is the result of defect interactions. Pair formation is the most common mode of clustering. Let us distinguish the following situations a) two point defects of the same sort form a defect pair (B + B = B2 = [B, B] V+V = V2 = [V, V]) and b) two different point defects form a defect pair (electronic defects can be included here). The main question concerns the (relative) concentration of pairs as a function of the independent thermodynamic variables (P, T, pk). Under isothermal, isobaric conditions and given a dilute solution of B impurities, the equilibrium condition for the pair formation reaction B + B = B2 is 2-pB = The mass balance reads NB + 2-NBi = NB, where NB denotes the overall B content in the matrix crystal. It follows, considering Eqns. (2.39) and (2.40), that... 

Let. us finally include higher clusters in the discussion. In kinetics, they are mainly relevant because the mobility of clustered point defects is quite different from the mobility of single defects. We shall treat the simplest possible situation. A matrix crystal A contains impurities B which form associates B, n = 2,3,. ... The total impurity content N% is given by n-Ns. The formation equation of B is... 

There is still another type of internal solid state reaction which we will discuss and it is electrochemical in nature. It occurs when an electrical current flows through a mixed conductor in which the point defect disorder changes in such a way that the transference of electronic charge carriers predominates in one part of the crystal, while the transference of ionic charge carriers predominates in another part of it. Obviously, in the transition zone (junction) a (electrochemical) solid state reaction must occur. It leads to an internal decomposition of the matrix crystal if the driving force (electric field) is sufficiently high. The immobile ionic component is internally precipitated, whereas the mobile ionic component is carried away in the form of electrically charged point defects from the internal reaction zone to one of the electrodes. 

Internal nucleation and growth can occur coherently or incoherently while the reaction volume can be negative or positive. The severe constraints which the matrix crystal exerts on the internal reaction can lead to the formation of metastable (or even unstable) phases, which do not exist outside the matrix. Often, heavy plastic flow and anisotropic growth has been found. 

Figure 9-12. a) Scheme of the internal solid state reaction CaO +Ti02 = CaTi03 in the matrix crystal NiO. Concentration profiles and precipitate are indicated, b) Photograph of cross section with internal reaction zone (T = 1340 C, t = 413 h reaction time). 

Figure 9-13. Concentration profiles and solubility product Lab = Na -Nh of solutes A and B in the matrix crystal C.

In Eqn. (14.19), which is the fundamental equation for transport in systems with inhomogeneous stresses, it is assumed that >, does not depend on concentration. This is obviously true for our dilute solution of species i in the matrix crystal. Correspondingly, we may also assume that fj is independent of the concentration of i. 

For nuclei that are coherent with the surrounding crystal, the lattice is continuous across the a//3 interface. The jumps controlling the /3C frequency factor will then be essentially matrix-crystal jumps and /3C will be equal to the product of the number of solute atoms surrounding the nucleus in the matrix, zcXg, and the solute atom jump rate, T, in the a crystal. The jump frequency can reasonably be approximated by T Di/a2 (see Eq. 7.52, where D is the solute tracer diffusivity and a is the jump distance). Therefore,... 

The growth of spherical precipitates under diffusion-limited conditions has been observed in a number of systems, such as Co-rich particles growing in Cu supersaturated with Co (see Chapter 23). In these systems, the particles are coherent with the matrix crystal and the interfaces possess high densities of coherency dislocations, which are essentially steps with small Burgers vectors, The interfaces therefore possess a high density of sites where atoms can be exchanged and the particles operate as highly efficient sources and sinks. 

I, 3-diene polymerization. Monomer molecules are included in chiral channels in the matrix crystals, and the polymerization takes place in chiral environment. The y-ray irradiation polymerization of trans- 1,3-pentadiene included in 13 gives an optically active isotactic polymer with a trans-structure. The polymerization of (Z)-2-methyl-1,3-butadiene using 15 as a matrix leads to a polymer having an optical purity of the main-chain chiral centers of 36% [47]. 

Figure 9 Illustration of the combined SPR-based BIA/MS approach (139). Deriva-tized biosensor chips, having multiple (2-4) flow cells each, are used in the real-time SPR-BIA analysis of interactions between surface-bound receptors and solution-phase ligands. The sensor chips are removed from the biosensor after SPR-BIA, with ligands still retained within the flow cells, and prepared for MALDI-TOF by application of an appropriate matrix to the flow cells. The matrix solution disrupts the receptor-ligand interaction, liberating the ligand into solution for incorporation into the matrix crystals. With proper application of the matrix, the crystals settle onto the original location of the interaction and spatial resolution between flow cells is preserved. The flow cells are targeted individually during MALDI-TOF and the retained ligand(s) are detected at precise and characteristic m/z values.

Luxembourg S, McDonnell L, Duursma M, Guo X, Heeren R (2003) Effect of local matrix crystal variations in matrix-assisted ionization techniques for mass spectrometry. Anal Chem 75 2333-2341. doi 10.1021/ac026434p... 

MALDI is achieved in two steps. In the first step, the compound to be analysed is dissolved in a solvent containing in solution small organic molecules, called the matrix. These molecules must have a strong absorption at the laser wavelength. This mixture is dried before analysis and any liquid solvent used in the preparation of the solution is removed. The result is a solid solution deposit of analyte-doped matrix crystals. The analyte molecules are embedded throughout the matrix so that they are completely isolated from one another. 

MALDI is relatively less sensitive to contamination by salts, buffers, detergents, and so on in comparison with other ionization techniques [41], The analyte must be incorporated into the matrix crystals. This process may generally serve to separate in solid phase the analyte from contaminants. However, high concentrations of buffers and other contaminants commonly found in analyte solutions can interfere with the desorption and ionization process of samples. Prior purification to remove the contaminants leads to improvements in the quality of mass spectra. For instance, the removal of alkali ions has proven to be very important for achieving high desorption efficiency and mass resolution. 

Solid state lasers CW or pulsed lasers in which the active medium is a sohd matrix (crystal or glass) doped with an ion (e. g., Nd, Cr, Er ). The emitted wavelength depends on the active ion, the selected optical transition, and the matrix. Some of these lasers are tunable within a very broad range (e.g., from 700 to 1000 run for Ti doped sapphire). 

USAL has also been used in the determination of trace impurities in high-purity materials. This type of analysis is mandatory with a view to controlling their quality and studying the synergistic action of, and correlation with, impurities. The accuracy and precision of the analytical results depend strongly on the particular separation procedure used before the determination step, as shown in the multi-element quantitative USAL of impurities such as iron, copper, lead and bismuth in high-purity silver metal. For this purpose, a silver sample was dissolved in nitric acid and treated with chloride, after which the solution was evaporated to dryness and the impurities were redistributed on the surfaces or in the interstitial spaces of agglomerates of matrix crystals. Then, the impurities were leached into 0.1 M nitric acid with the aid of ultrasonic irradiation [91]. 

Crystal shape, size, and density all affect the physical properties of the final solid fat matrix. Crystal growth, primary nucleation, and secondary nucleation in fat systems are influenced by many factors, including diffusion, molecular compatibility, TAG structure, nuclei composition and surface properties, number of nuclei, and processing conditions (temperamre and/or shear) (38, 39). It is during the crystallization process of fats that the template for the final physical properties of the material is created. 

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