Scintillation solvents

Color quenching is a problem if chemical substances that absorb photons from the secondary fluors are present in the scintillation mixture. Since the secondary fluors emit light in the visible region between 410 and 420 nm, colored substances may absorb the emitted light before it is detected by the photocells. Radioactive samples may be treated to remove colored impurities before mixing with the scintillation solvent. 

Scin Sd. [Monomer-Polymer St Ditjac Labs] Scintillation solvent... 

For homogeneous sample counting the radioactive material must be soluble in the organic scintillation solvent (toluene, xylene, dioxane). Unfortunately most inorganic salts, hydrophilic substances, macromolecules (such as proteins, nucleic acid or polysaccharides) or biological tissues (muscle, bone, liver, brain) and body fluids (blood, plasma, urine, spinal fluid) are incompatible with the solubility characteristics of the liquid scintillant. To overcome these problems various useful methods for tissue preparation have been developed such as solubilisation by hydrolysis, wet oxidation, combustion. 

Benzene serves well in this capacity as a scintillation solvent and is used by many dating laboratories. The chemistry of benzene synthesis involves quantitative conversion of the sample specimens to carbon dioxide (De Vries, 1955 Rafter, 1954) followed by conversion to acetylene (Barker, 1953 ... 

Two approaches have been used to eliminate this problem. The historic approach was to add small, polar organic molecules miscible with both water and scintillator solvents... 

As for paper chromatograms, thin layer plates may be placed in a tank containing scintillator and covered with x-ray film. This procedure is unsuitable for fragile adsorbents or for substances which diffuse or dissolve in the scintillator solvent. 

Figure 2. Thin-layer radiochromatogram of urine (100 il) from rats injected with labeled PbTx-3. TLC plates were developed in two sequential solvent systems chloroform ethyl acetate ethanol (50 25 25 80 10 10). Radioactive zones were scraped and counted in a liquid scintillation counter. Native PbTx-3 runs at 13 cm.

Using a simple solvent extraction procedure to minimize matrix effects, a diclofop-methyl immunoassay was developed for milk, a number of edible plant products, and other matrices. Gas chromatography (GC) and liquid scintillation counting (LSC) of a C-labeled analyte were used as reference methods to compare with enzyme immunoassay (EIA) results. The methods were well correlated, with comparison of EIA... 

Urine Sample wet ashed, purified by solvent extraction Liquid scintillation 14 pCi/100 cm3 96% at 20,000 dpm spike Ham et al. 1977... 

Soft tissue Sample wet ashed, purified by solvent extraction a -Liquid scintillation 0.7 pCi/g 99% at 3,000 dpm spike Guilmette and Bay 1981... 

For the analysis of americium in water, there is a broad array of sample preparation and detection methodologies that are available (see Table 7-2). Many of the common and standardized analytical methodologies typically include the minimization of sample volume, purification through co-precipitation, anion exchange column chromatography, and solvent extraction techniques followed by radiochemical detection of americium in the purified sample. Gross alpha analysis or liquid scintillation are common... 

Air Sample collection on cellulose filter, dry ashed, solvent extracted Biphasic liquid scintillation 1 pCi 95% Bomben et al. 1994... 

Guilmette RA, Bay AS. 1981. Radio assays of americium or curium in biological material by isoctyl acid phosphate solvent extraction and a liquid scintillation counting. Anal Chem 53 2351-2354. 

Forster (1968) points out that R0 is independent of donor radiative lifetime it only depends on the quantum efficiency of its emission. Thus, transfer from the donor triplet state is not forbidden. The slow rate of transfer is partially offset by its long lifetime. The importance of Eq. (4.4) is that it allows calculation in terms of experimentally measured quantities. For a large class of donor-acceptor pairs in inert solvents, Forster reports Rg values in the range 50-100 A. On the other hand, for scintillators such as PPO (diphenyl-2,5-oxazole), pT (p-terphenyl), and DPH (diphenyl hexatriene) in the solvents benzene, toluene, and p-xylene, Voltz et al. (1966) have reported Rg values in the range 15-20 A. Whatever the value of R0 is, it is clear that a moderate red shift of the acceptor spectrum with respect to that of the donor is favorable for resonant energy transfer. 

Concentrations of radiolabeled proteins, substrates, or products can be quantified by scintillation counters, which detect both emitters of weak (e. g., 3H) and high energy (e.g., 32P) by excitation of an organic solvent (e.g., toluene) which then emits fluorescence fight. In commercial systems the primary fluorescence is transformed via one or two additional fluorescent dyes in the solution into a visible emission signal which can easily be detected by conventional photomultipliers. 

Weak beta radiation and alpha particles often cannot penetrate the covering material but the use of a scintillant, which, together with the sample, will dissolve in a suitable solvent, enables a similar technique to be used. Liquid scintillation counters usually consist of two light-shielded photomultiplier... 

The functions of the solvent are to keep the scintillator or solute in solution, and to absorb the decay energy of the radioisotope for subsequent transfer to the solute. Solvents fall broadly into three categories ... 

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