Quenching problem

Once again, the most recent developments have been in the area of green phosphorescent materials where phenomenal efficiencies are now beginning to be coupled with good device lifetimes. The prototypical emitter of this type is iridium-tris-2-phenylpyridine (Ir(ppy)3) used as a dopant (Scheme 3.98), usually diluted into a carbazole type host, because it is prone to serious self-quenching problems. 

A second way to resolve quench problems is to separate the sterols from the pigments by thin layer chromatography (TLC). Briefly, samples are concentrated by evaporation and redissolved in a small volume (<100 xl) of chloroform or hexane and spotted onto a pre-dried, silica gel G, TLC plate along with 5 xg of cholesterol standard. Components are resolved with a mobile phase comprised of petroleum ether, diethyl ether, and acetic acid at a 300 200 1 ratio. Sterols migrate 1/4 to 1/3 of the way to the top of the plate, while pigments stay at or near the origin. Spots are visualized with iodine vapor, marked with a pencil, scraped into scintillation... 

For certain special cases, going to the high intensity limit provides a remarkably simple solution to the quenching problem.. 

It has long been recognized that both the diffuse spectra and quenching problems can be alleviated by performing the fluorescence measurement in a low-temperature solid matrix, rather than in a fluid solution. The most common low-temperature matrices used in molecular fluorometric analysis are frozen liquid solutions the analytical characteristics of frozen-solution luminescence spectrometry have been discussed extensively in the literature (2-10). Obviously, MI represents an alternative technique to use of frozen liquid solutions for low-temperature fluorometric analysis. There are two principal advantages of MI over frozen-solution fluorometry. First, in MI, any material which has an appreciable vapor pressure at room temperature can be used as a matrix one is not limited by the... 

Third, difficult samples of materials containing 3H or 14C (e.g., tissue slices, etc.) can be converted to 3H20 or 14C02 in commercially available sample oxidizers. These units burn samples under controlled conditions and then separate the 3H20 and the 14C02 for counting in an acceptable scintillation cocktail. Sample oxidation also eliminates color-quenching problems. 

Studying the Na-N2 quenching problem, Bauer et al. (1969) reduced the multidimensional problem to the crossing of an array of one dimensional... 

Many of the quenching problems discussed above can be lessened if an experiment is carefully planned. A wide variety of sample preparation methods and scintillation liquids are available for use. Some of the more common techniques are mentioned below. 

The answer to the quenching problem may lie in an intrachain or interchain interaction in the copolymer that is independent of atmosphere. One possibility is an internal photocyclization to a 3,4-dihydro-l(2ff)-naphthaleneone structure ... 

Quenching problems can be reduced by using a two-flame construction where the first flame pyrolyzes the compound and the second excites the decomposition products. 

While safe, conventional fluoroimmunoassays are beset by background and quenching problems. 

Referring to magnetic resonance methods, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy, and particularly NMR, is widely used for reaction monitoring however, it is not applicable to all nuclei, and quenching problems may occur in the presence of paramagnetic species. On the other hand, EPR spectroscopy can only detect systems with unpaired electrons. This limits the application potential for this method, and additional complementary... 

The remarkable feature of the effective Hamiltonian is that there are now two new types of attractive interaction one of which involves three chains, while the other one couples four chains together, similar to the 2-chain quenched problem. 

Antigen-antibody reactions occur in aqueous solution. Therefore, after separating "free" and "bound" radioactivity in a radioimmunoassay, one must frequently measure the radioactivity of an aliquot of an aqueous solution. Here we are faced with the problem of dispersing water, a polar solvent, in a non-polar toluene or xylene based scintillator system. To minimize quenching problems, especially serious when counting weak beta particles such as those emitted by tritium, it is best if a homogenous mixture of the sample and liquid scintil-lant results. That is, two-phase systems should be avoided if possible. 

Because both of these reagents exhibit fluorescence quenching, problems arise in the determination of lysine and cysteine. Since they also react only with primary amines, special steps must be undertaken to detect proline. 

The thermal birefringence was calculated based on a linear viscoelastic and a photoviscoelastic constitutive equation as given in [7] along with a measured stress- and strain-optical coefficient functions [8]. For a onedimensional quenching problem... 

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