Liquid scintillation homogeneous

A drin and Dieldrin Metabolism.— The in vivo metabolism of the chlorinated alicyclic insecticides, aldrin and dieldrin, has been measured. Fish were exposed to l c-labelled aldrin or dieldrin for 6 hours. The metabolism of each compound was monitored by thin layer chromatography of hexane and chloroform-methanol extracts of liver homogenates, followed by liquid scintillation counting of the spots (5,15,16). 

On-line detection can be classified as either homogeneous or heterogeneous. In the homogeneous system, the effluent is mixed with a liquid scintillation cocktail before passing through a flow cell that is positioned in a scintillation counter. In the heterogeneous system, the effluent passes through a flow cell packed with a solid scintillator. 

Calcium chloride solutions (pH =6.2) labeled with Ca or 36ci were displaced vertically downward through columns of homogeneous, repacked, water-saturated sandy soil by a chemically identical solution labeled with Cl or Ca, respectively. Constant water fluxes, and solution activities of 1 to 15 pCi/dm, were used. Calcium solutions were analyzed by titration with disodium dihydrogen ethylenediamine tetraacetate to a murexide end point (11). The activity of radioactively labeled solutions was obtained by liquid scintillation techniques. Concentrations of adsorbed calcium were calculated from isotope dilution. The concentration of calcium chloride in the influent solution was 0.08 N. Because exchange of calcium for itself was the only chemical process affecting transport, the calcium chloride concentration remained constant at 0.08 N throughout each experiment, both within the column and in the effluent. 

Soluble radioactive strontium can be detected in urine, blood or feces by liquid scintillation counting. Whole body counters (or chest counters for inhalation exposures) can measure internal radioactive strontium deposited in bone following high level exposures (see Section 7.1.1). Children tend to incorporate strontium more homogenously throughout bone than is the case for adults. 

Each animal was sacrificed by captive bolt after the appropriate withdrawal interval (4, 6, 14 and 28 days after the 2nd dose) and processed as in an abattoir. The entire liver, kidneys and udder were excised and 1-2 kg samples of muscle from both the flank and the udder diaphragm and 1-2 kg samples of fat from the abdominal area were collected. Each organ and tissue was minced and processed three times through a commercial meat grinder to prepare respective homogenate samples. Sub-samples (200-300 mg) were prepared in triplicate for total residue analysis. Total radioactivity concentrations, expressed as pirlimycin free base equivalents, were determined by direct liquid scintillation counting (liquids) or combustion analysis (solids) following standard techniques. 

In brief, this involved spiking homogenized tissues with non-radiolabeled reference compounds, methanol extraction, hexane-water partitioning followed by reverse phase chromatography (XAD-2 and C-18 HPLC). The activity in each fraction was quantified by liquid scintillation counting. 

In vitro and in vivo release kinetics were compared using two different approaches. In the first approach (the recovery approach) polymer implants containing a radioactively labeled substrate—,4C-labeled bovine serum albumin, /3-[14C]-lactoglobulin, or [3H]-inulin—were implanted subcutaneously into rates (in vivo) or released in phosphate-buffered saline, pH 7.4, at 37°C (in vitro). At various time points, the polymer implants were removed from the rats or the saline. They were then lyophilized to remove residual water and dissolved in xylene. When the polymer dissolved, the unreleased macromolecules precipitated to the bottom of the vial. Water was then added to dissolve the macromolecules scintillation fluid was next added, resulting in a homogeneous translucent emulsion which was counted via liquid scintillation. 

Homogeneous. The eluate is mixed with liquid scintillant before passing through the flow cell. The sample is passed to waste after counting. 

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. 

The liquid scintillation technique was utilized in the case of thymidine or DNA labelled with or Measurements in the homogeneous phase have shown that the counting efficiencies depend on two variables the 3 particles energy and the size of the molecule carrying the radioisotope. In the homogeneous phase, measurements are correct only if the liquid scintillation medium and the radioactive solution added give rise to a medium which is homogeneous, not only at the macroscopic level, but also at the molecular level. Experiments performed have shown that, for small sized molecules (like... 

The experimental difficulties encountered using the homogeneous phase method have shown that these measuring conditions are valid only if the homogeneity of the radioactive aqueous solution and the liquid scintillator selected is maintained, not only at the macroscopic level, but especially at the molecular level. Further, these difficulties have shown that the calibrations carried out with small sized molecules (tri-tiated water, -or C- thymidine, for example) are not necessarily valid in the case of large sized molecules (DNA, for example), because of the physico-chemical properties of macromolecules. Finally, these difficulties have shown that the measurement artefacts encountered are not revealed by the standard methods of analysis and correction. 

The same radioactive atom can, therefore, give two different results, depending on the molecule which carries it. In liquid scintillation, the results of the homogeneous phase measurements do not, therefore, depend only on the energy of the 3 particles emitted by the radioactive isotope, but also on the size of the radioactive molecule. The difficulties encountered in the case of DNA appear to be a consequence of the physico-chemical properties of the macromolecules in general, and should be evidenced as well in the case of RNA or of proteins. 

Sample Holding Capacity (SHC). SHC can be defined as the minimum volume of scintillator required to keep sample in a homogeneous form, suitcible for liquid scintillation counting. Miniaturizing requires considerable sample holding capacity for various types of biological samples. 

Emulsion counting utilizing toluene based counting solutions which can accomodate milliliter quantities of aqueous samples has become an important technique in liquid scintillation spectroscopy (2-11). This technique is based on the fact that in the presence of non-ionic surfactant, such as Triton X-100, in toluene solution, relatively large volumes of aqueous radioactive samples form homogenous solutions, which allow measurement of the radioactivity under well reproducible conditions. 

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. 

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