Transparent matrices

In comparison with hydrocarbon and polymeric matrices, which have their own absorptions in the IR and can react chemically with the intermediates, inert gas matrices are free of these shortcomings. Neon, krypton and xenon have been used as matrix substances in some studies. However, only argon and nitrogen matrices are widely adopted because of the availability of the pure gases and the fact that there is a variety of cryostats that can provide the optimal temperature conditions for the formation of rigid and transparent matrices from these elements. 

PTFE is commercially available in three forms (1) skived films (2) powder and (3) aqueous dispersions. Of the three forms, the aqueous dispersion provides the most suitable medium to approach a level of mixing and uniformity of the host matrix and dopant that is achieved when transparent matrices and sensitizers share... 

The generation of ion radicals usually proceeds in frozen diluted solutions at 77 K and under irradiation for not more than half an hour. An ion radical concentration of 10 4-IO 3 is reached, which is sufficient to record optical or ESR spectra of the ion radicals. The solvents must form transparent matrices as they get cold. For example, THF gives... 

In this method,the sample can be analyzed either directly in bulk form or as dispersions in IR transparent matrices such as KBr and KCl. Sometimes, a thin film of KBr powder placed on the sample surface to improve the quality of the spectrum. Dilution of analyte in a nonabsorbing matrix increases the proportion of diffuse reflectance in the reflected light. Typically, the solid sample is diluted homogeneously to 5 to 10% by weight in KBr. The spectra of diluted samples are similar to those obtained from pellets when plotted in units such as log 1/R (R is the reflectance) or Kubelka- Munk units. 

Opaque matrices are a methodological problem not only in the analysis of captured tissue cells but also in normal MALDl tissue imaging, when areas of interest must be positioned correctly after matrix application. Sweedler and coworkers have sought transparent matrices layers as substitutes for regular MALDl matrix substances [53]. The addition of triethylamine to solutions of standard MALDl matrices led to the formation of ionic liquids [54], and this was reported to result in favorable MALDl imaging performance. 

The sol-gel process is a solution synthesis technique which provides a low temperature chemical route for the preparation of rigid transparent matrices. A number of laser dyes have been incorporated in different sol-gel matrices and tunable laser action has been demonstrated with these materials. 

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