Sample Channels Ratio Research Articles

The effects of nonuniform quencher distributions in quencher concentration measurements using liquid scintillation techniques

The use of liquid scintillation counting techniques for the in-situ measurement of quencher concentration in studies of transport phenomena was investigated. Quencher concentration gradients cause complex distortions of the measured scintillation pulse height spectrum. The measurement of the average quencher concentration using either sample channels ratio (SCR) or external standard channels ratio (ESCR) calibrations is unreliable if gradients are present, whereas measurement of the sample activity appears to remain unaffected by such gradients. It is suggested that case-specific test measurements be made on heterogeneous samples prior to the use of scintillation methods for in-situ measurement of quencher concentration.

Programmable calculator software for computation of the plasma binding of ligands

The computation of the extent of plasma binding of a ligand to plasma constituents using radiolabeled ligand and equilibrium dialysis is complex and tedious. A computer program for the HP-41C Handheld Computer Series (Hewlett-Packard) was developed to perform these calculations. The first segment of the program constructs a standard curve for quench correction of post-dialysis plasma and buffer samples, using either external standard ratio (ESR) or sample channels ratio (SCR) techniques. The remainder of the program uses the counts per minute, SCR or ESR, and post-dialysis volume of paired plasma and buffer samples generated from the dialysis procedure to compute the extent of binding after correction for background radiation, counting efficiency, and intradialytic shifts of fluid between plasma and buffer compartments during dialysis. This program greatly simplifies the analysis of equilibrium dialysis data and has been employed in the analysis of dexamethasone binding in normal and uremic sera.

Quench correction of incorporation carbon-14 in Aspergillus nidulans counted on filter discs

We have developed a convenient method for 14C quench correction for Aspergillus nidulans counted in liquid scintillator using disc technique. By comparing intact and solubilized samples labelled to constant specific activity, a quench correction factor (QCF) was obtained for a range sample sizes. Large differences, in quenching, including sample self-absorption, were found amongst ungerminated conidiospores and mycelia of different ages and also amongst strains of different genotypes. The sample channels ratio (SCR) method of quench correction was shown to be inadequate (even for extremely low weights of conidiospores and mycelia). The correlation between sample dry weight and sample channels ratio of standards, once established, can adapted to form a convenient means of determining sample size, and hence specific activity, by counting alone. As a cautionary example, a study of d-glucose uptake by conidiospores and mycelia of wild-type and certain carbon catabolite derepressed mutants is presented. Whereas the uncorrected data suggest an uptake defect in the mutants, no such deficiency is apparent after applying QCF. This method should be suitable for other fungi and for other low energy β-emitting nuclides.

Detector-ratio and discriminator-ratio methods in dual-label counting

The ratio of net Geiger-Müller to net solid-scintillation counts (GM/SS) for a mixture of two isotopes and for given counting times is linearly proportional to the fraction of the total net counts of either isotope in the SS detector. The reciprocal ratio (SS/GM) is linearly proportional to the fraction of the total net counts of either isotope in the GM detector. These simple, straight-line relationships can be used to resolve dual-labelled mixture of β-γ isotopes with single-channel analyzers and relatively inexpensive detectors. The method allows each detector to respond to both isotopes. A similar relationship can be used for resolving dual-labelled mixtures of β-isotoped by liquid-scintillation counting. In this case, the sample channels ratio, C1/C2, is linearly proportional to the fraction of the total net counts of either isotope in channel 2. This relationship is a corollary of the “discriminator-ratio” method in liquid-scintillation counting.

Direct determination of32P or36Cl in tissue solubilizer solutions by Cherenkov-scintillation counting

Phosphorus-32 and chlorine-36 radioactivity was measured directly in commercially available tissue solubilizers using a liquid scintillation counter. Various wavelength-shifting compounds: β-naphthol, 4-methylumbelliferone, 7-amino-1,3-naphtalenedisulfonic acid, 2-hydroxy-3,6-naphthalenedisulfonic acid, anthranilic acid and salicylic acid were investigated to assess their suitability for the improvement of counting efficiency. Salicylic acid was selected which is fairly stable in alkaline solutions of tissue solubilizers and remarkably improves counting efficiency up to 90% for both nuclides. 0.1 g of soft tissues or blood can be solubilized with 1 cm3 of tissue solubilizer containing 2 g/dm3 of salicylic acid directly in 6 cm3 scintillation minivials. The sample channels ratio method for colour quench correction was found to be satisfactory.

The contribution of the counting vial to variable quench in Cerenkov counting

Evidence for significant variation in counting efficiency within and between batches of glass and plastic vials is presented. Effective corrections for the consequential potential errors can be made by means of appropriate quench curves using a sample channels ratio technique.

Liquid scintillation counting of radionuclides emitting high-energy beta radiation

Liquid scintillation counting of radionuclides emitting beta radiation with Emax>2 MeV has been investigated. Fluor volume effects were similar to those for low energy beta radiation, and pulse height spectra broadened in a predictable manner with no pulse clipping up to 4.913 MeV. Large changes in sample channels ratio due to color quenching resulted in progressively smaller losses of counting efficiency as beta energy increased. Counting efficiences were estimated to be near 100 percent for34Clm,36Cl,32P and38Cl. Cerenkov counting of38Cl by liquid scintillation counter was volume dependent for both counting efficiency and pulse height spectrum. Counting efficiencies for34Clm,36Cl,32P and38Cl were estimated to be 57.0, 7.5, 42.7 and 66.3%, respectively. Pulse height spectra were shifted to greater pulse heights as a function of beta Emax, supporting the possibility of energy discrimination for beta emitters by Cerenkov pulse height spectrum analysis. The advantage of singles Cerenkov counting over coincidence Cerenkov counting was greatest for36Cl and least for38Cl; this advantage was amplified more for samples of36Cl which had been color quenched than for similarly quenched samples of38Cl or32P.

Determination of phosphorus-32 and calcium-45 in biological samples by Čerenkov and liquid scintillation counting

A practical procedure is described for the determination of 32P and 45Ca in various biological samples. Samples were wet-ashed with 70% HClO 4 and 30% H 2O 2. The activity of 32P was estimated by Čerenkov counting and sum of the activities of both the nuclides were measured by liquid scintillation technique after addition of the “Aquasol”-solgel scintillator. Quench correction was accomplished by the sample channels ratio and by the automatic external standard channel ratio in the <Cerenkov and scintillation technique respectively. The recoveries of both nuclides obtained in biological samples of various origin (0.995 for 32P and 0.960 for 45Ca) indicate the suitability of this method for the simultaneous determination of these nuclides.

Solving the problems of counting 14CO 2 produced in biological experiments

14 CO 2 can be trapped efficiently as Na 2 14 CO 3 in aqueous solutions of NaOH. In this state it can be dispensed and counted with great accuracy and stability, provided the correct conditions are observed. In this paper the various separate causes of inaccuracy in handling and counting 14 CO 2 are explained and demonstrated. These include the rapid loss of 14 CO 2 from aqueous solutions of mid-range pH, the effects of varying the constitution of the mixture being counted, the use of high specific activity Na 2 14 CO 3 , adsorption on the surface of the vial, the misuse of the “merit value” concept, and the effect of the dimensions of the counting vials on the rate of change of counting efficiency with volume of scintillant. The relevance of these conclusions to the work of other authors in this field is discussed. An account is given of some satisfactory procedures for counting 14 CO 2 using both commercial liquid scintillation fluids and “home made” mixtures. The applicability of the sample channels ratio and external standard channels ratio techniques to these mixtures is discussed. A method is described for the separation of 14 CO 2 from larger amounts of 14 C labelled volatile fatty acids and alcohols, which may have been either evolved or used as substrates in biological experiments.

Simultaneous determination of phosphorus-32 and calcium-45 activity in biological samples

Using the technique of liquid scintillation,32P and45Ca activites were determined in biological samples such as bones, blood, milk and egg shells, white and yolk. Samples were mineralized in 70% HClO4 and 30% H2O2 at 70 °C and measured after addition of the “Aquasol” scintillation liquid. A correction for quenching was made by the method of sample channels ratio. High detection efficiencies were obtained, above 80% for45Ca and about 50% for32P in a second measuring channel. Recoveries amounted to 0.95–1.06 for32P and to 0.93–0.98 for45Ca.

The effect of volume and quenching on estimation of counting efficiencies in liquid scintillation counting

The effect of volume on the liquid scintillation counting performance of 14C-samples has been investigated. A decrease in counting efficiency was observed for samples with volumes below about 6 ml and those above about 18 ml when unquenched samples were assayed. Two quench-correction methods, sample channels ratio and external standard channels ratio, and three different liquid scintillation counters, were used in an investigation to determine the magnitude of the error in predicting counting efficiencies when small volume samples (2 ml) with different levels of quenching were assayed. The 2 ml samples exhibited slightly greater standard deviations of the difference between predicted and determined counting efficiencies than did 15 ml samples. Nevertheless, the magnitude of the errors indicate that if the sample channels ratio method of quench correction is employed, 2 ml samples may be counted in conventional counting vials with little loss in counting precision.

Cryptic “photon” quenching in dioxane-based liquid scintillation mixtures

Dioxane-based scintillation mixtures containing β-emitting radioisotopes show a decreased efficiency under the following conditions: low water concentration in the sample, the presence of some metal ions, e.g., Ca2+, Mg2+, and certain3H- and 14C-labeled compounds, e.g., nucleotides. If only one of the preconditions was not fulfilled, the effect disappeared. There is no visible sign of any form of sample inhomogeneity, and the composition of the scintillation sample gives no reason to suppose that a special sort of quenching would occur. In addition, no commonly used standardization method, such as external standard channels ratio, internal standard, or sample channels ratio could be used to detect this sort of quenching, to say nothing of correcting for it. A further analysis shows that the decreased count rate has to be explained by a special sort of “photon” quenching. The so-called “double ratio plot” proposed by Bush ((1968) Int. J. Appl. Radiat. Isotop.19, 447–452) to provide an indication of sample heterogeneity failed to indicate this sort of photon quenching.

Effects of permeability of polyethylene vials in liquid scintillation counting

The effects of the permeability of polyethylene counting vials on the liquid scintillation counting of radioactive materials and channels ratios have been examined. The count rate of toluene-soluble and water-soluble radioactive material dissolved in a suitable scintillation mixture altered by not more than 5 per cent in 4 days. The sample channels ratio altered only slightly or not at all. Changes in external standard channels ratio varied between 3 and 25 per cent in that time, depending on scintillation mixture and temperature of storage. Changes were in all cases greater if vials containing prepared samples were kept at 20°C than if they were kept at 5°C. If n-hexadecane radioactive standard was dispensed into empty polyethylene vials there was a reduction in counting efficiency related to the delay before adding scintillation mixture; the efficiency fell 5 per cent within 2 hr.

Computerized assay of doubly labeled liquid scintillation samples

The use of computer programs for the analysis of liquid scintillation data from double label experiments is described. Suggested experimental procedures for double label counting of various combinations of 32P, 14C and 3H by the external standard ratio method and the sample channels ratio method are presented. A means for extending the useful range of the latter method is described in detail. Experimental results demonstrating the effects of quenching and isotope overlap are shown.

Automatic quench correction by channels ratio for both carbon-14 and tritium using a three channel liquid scintillation counter

Calibration of a three channel liquid scintillation counter for sample and external standard channels ratio quench correction is described. Calibration curves, enabling both carbon-14 and tritium activities to be corrected for quenching without altering instrument settings, are modelled by computer. Data from the counter can be precessed rapidly using a ready-access desk-top computer. The advantages of the method, the potential accuracy obtainable, and some applications are discussed.