Scintillation counting fluid

The use of emulsion liquid scintillation counting fluids to count Na2 C03 in the absence of NaOH or any other base is still current practice (Major, 1979 Mayobre et ai, 1979), despite the fact that several studies have shown that this method is subject to serious errors (MacRae and Wilson, 1978 Huskisson and Ward, 1978 Herbland, 1977 Murray, 1971). 

The efficiency of the cDNA probe synthesis is determined by scintillation counting of the flowthroughs from steps 9 and 11 5pL of each flowthrough are added to 5mL scintillation fluid in separate scintillation counter vials. The samples are counted on the P-channel, and the obtained counts are multiplied by a dilution factor of 20. Probes should yield a total of 5-25 x 10 cpm see Note 32). 

Pipette carefully 400 pi from the upper phase (total volume 675 pi) in scintillation vials and add counting fluid suitable for counting water containing samples (Ultima Gold) measure the radioactivity in a scintillation counter. 

In a passive detector developed by the National Radiological Protection Board (Wrixon et al., 1988), the etched pits in the detectors are filled with scintillator fluid. After exposure to radon, the detector is irradiated with an alpha source, and the resulting scintillations counted with a photo-multiplier tube. In this way, track density over 1 cm2 of detector can be measured in a few seconds. Passive detectors used in the UK National Survey were sensitive down to 20 kBq m-3 h of accumulated exposure, equivalent to a radon concentration of 5 Bq m-3 measured over 4000 h exposure. 

Measurement of radioactive decay can also be affected by various components present in, or added to, the scintillation cocktail. These components can cause quenching that is, they can decrease the efficiency of the scintillation process. Scintillation counting provides data in counts per minute (cpm). Quenching dictates that the counts per minute detected is less than the actual decay rate, or disintegrations per minute (dpm). Almost every sample encountered experimentally is quenched to some degree for example, 02 picked up by the scintillation fluid from contact with air serves as a quencher. Therefore, researchers frequently count an additional sample containing a standard of known de-... 

Incomplete solubility and associated point quenching constitute a major problem in scintillation counting. Efficient scintillation counting requires that the sample be fully soluble in the excitable organic solvents of the scintillation fluid. However, biological systems, which are usually aqueous systems or assays, frequently contain water or hydrophilic molecules that will not dissolve in standard toluene-based scintillation cocktails. 

Figure 1.1 Schematic of a representative enzymatic assay. The reaction mixture is prepared (Mix Preparation) and the reaction can be started (Initiation) by the addition of the enzyme. During the reaction (Incubation), samples are removed at intervals labeled h, t2, and r3, and the reaction is stopped (Termination) by inactivating the enzyme. The incubation mixture is fractionated (the illustration shows a traditional chromatographic column), and the product is isolated from the substrate (Separation). In this assay, a radiochemical was used as the substrate and therefore the amount of product that formed is determined by its collection, the addition of scintillation fluid, and the measurement of radioactivity by scintillation counting (cpm Detection). The progress of the reaction is given by the amount of radioactive product recovered (Data Reduction).

The presence of inert material or colored material in a sample may reduce the radioactivity observed in scintillation counting. This quenching effect can be corrected for quite easily by means of an internal or added standard. The first thing to be sure of is that the samples are counted under the same conditions as the standards. For example, if the samples are 0.5 ml of an enzyme assay mixture (in aqueous buffer) that are added to 5 ml of scintillation fluid, then the specific activity of the standard should be determined in 0.5 ml of the same buffer, counted in 5 ml of scintillation fluid. 

Quantitate the radioactivity, as a measure of RT activity in 1 pL of the culture supernatant, either by liquid scintillation counting (cut out the spots and place them directly into scintillation fluid), by phosphorimage analysis and quantitation of relative pixel units, or by autoradiography and laser densitometry. 

Zhu M, Zhao W, Vazquez N, Mitroka JG. Analysis of low level radioactive metabolites in biological fluids using high-performance liquid chromatography with microplate scintillation counting method validation and application. J Pharm Biomed Anal 2005 39 233-245. 

Absorbable devices may be radiolabeled and the excreted amounts of material quantified by scintillation counts. Any radiolabeled material remaining in vivo may be visualized by radiography. Absorption rates are estimated by subcutaneous implantation and visual evaluation of shape, mass, and dye retention. Diffusion chambers are also used to prevent the host cells from encapsulating the absorbable material while allowing contact with tissue fluids. Chambers are placed subcutaneously or intraperi-toneally the absorbable material may be chemically evaluated on retrieval. 

Transfer 20 pi vesicles to a scintillation vial and add 12 ml of scintillation fluid determine the radioactivity by scintillation counting for 1 min. This should give upwards of 50,000 d.p.m., if not resonicate. Save the vial and recount for 10 min together with the test samples after the assay to give total counts. 

Radiolabeling Procedure. [ C]-Formaldehyde labeling of siuface A was performed in a self-fabricated metal sample holder with four wells (diameter = 7 mm). Acetonitrile (50 fiL) containing 10.0 mM NaBHsCN and 2.0 mM [ C]-formaldehyde was iiyected into each well. After incubation for 4 h at 20 °C, the excess radioactive solution was removed and the exposed surface washed with CH3CN 10 times and water 10 times. The demounted samples were extensively washed again with water and then dried with N2. The same procedure was also applied to the control surfaces of Ti and acetylated A The radioactivity of each sample was measured by scintillation counting in 5 mL of scintillation fluid (1080 mL of toluene, 920 mL of Triton X-100, 5.4 g of 2,5-diphenyloxazole, 0.2 g of l,4-bis-2-(5-phenyloxazolyl) benzene, and 40 mL of acetic acid) on a Tri-Carb 2300TR liquid scintillation counter (Packard Instrument Co., USA). 

Excretion Urine and other body fluid chemical analysis, LC-MS, HPLC, scintillation counting... 

Finally, radioactively labeled retinoids can be detected through scintillation counting. This can be done either by the collection of fractions for determination of radioactivity in a standard liquid scintillation counter or by using a flowthrough detector, in which the sample eluting from the HPLC column is mixed with a scintillation fluid and then passed directly through a counting chamber. 

For liquid scintillation counting or scintillation autoradiography, the areas of sorbent containing radioactive zones are scraped into vials and mixed with scintillation fluid. The light emitted because of interaction of radioactive nuclei with the fluid is measured with a photographic film or scintillation counter. 

In the author s laboratory, the elution of radiolabelled samples is measured by liquid scintillation counting. Aliquots of collected fractions are mixed wtih OptiPhase Safe (LKB) liquid scintillation fluid using a maximum of 1 vol. of sample to 10 vols of scintillant. 

Alternatively, [ C] Ac-CoA can be used as the donor substrate and nonradioactive Cm as the acceptor (5). With this assay format, the reaction mixture can be added to a toluene-based scintillation fluid and the [ C] Ac-Cm product can be counted directly since [ CJAc-Cm is far more soluble than [ C]Ac-CoA in toluene (6). More conveniently, the reaction product can be quantitated by liquid scintillation counting immediately after extraction into ethyl acetate (5). An improved version of this two-phase extraction strategy is the two-phase diffusion system in which the radiolabeled product is selectively diffused into the water-immiscible liquid scintillation cocktail (e.g., Econofluor, NEN) which is overlaid on the aqueous reaction mixture (7). The diffusion assay method allows for continuous and convenient data collection within minutes to several hours. 

First,freshly isolated lymphocytes obtained from a normal person were preincubated in 3H-hypoxanthine containing mediim, and then washed out several times. The last washing fluid was shown to contain no measurable radioactivity by liquid scintillation counting. The preincubated normal lymphocytes were then mixed with an approximately equal amount of untreated lymphocytes obtained from a Lesch-Nyhan patient. The cells were spun down to assure cellular contact. The cells were then fixed, treated with cold TCA, stained with or-ceine and subjected to autoradiography. 

The scintillation fluid is added and the solutions are counted for 10 minutes in Scintillation Counter. ... 

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