External Standard Channels Ratio Research Articles

Liquid scintillation counting of aqueous solutions of potassium salts in a Triton X-100/toluene scintillant

The use of a toluene/Triton X-100 scintillant for counting 14C in aqueous solutions of potassium salts including potassium hydroxide has been investigated. Suitable conditions for the counting of CO 2 entrapped in potassium hydroxide are described. Quench correction by automatic external standard channels ratio procedures has been found to be of value with optimised conditions of counting.

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.

Liquid scintillation counting in high-density polyethylene vials

It has been shown previously that both scintillation solvents and solutes diffuse into the walls of high-density polyethylene vials. This diffusion causes the plastic vial walls to act as a plastic scintillator, which has a much lower scintillation efficiency than the solution itself. The result is the observation of a time dependence of the external standard channels ratio (ESCR) value. The absolute change of the ESCR value and its rate of change is dependent on the choice of the external standard counting channels. It is shown that with the proper choice of the external standard counting channels, the time change of the ESCR value can be essentially eliminated for up to a 3-day time period. The diffusion process has also been shown to cause an increase in the measured background rate mainly in the tritium counting channel (i.e. low-amplitude pulses). The counting efficiency was unchanged over extended time periods (up to 12 days) even though appreciable amounts of the samples may also diffuse through the vial walls.

Elimination of Error Caused by Hemolysis and Bilirubin-induced Color Quenching in Clinical Radioimmunoassays

Abstract In radioimmunoassays and radioassays for various constituents of serum, color quenching is a source of error when liquid-scintillation methods are used in samples that contain hemolyzed blood and samples from jaundiced patients. A quench correction can be made by using the External Standard Channels Ratio method and normalizing the ratios, or, alternatively, by chemical decolorization with tetramethylammonium hydroxide, hydrogen peroxide, and ascorbic acid.

Data processing of triple labelled liquid scintillation samples

Procedures to analyse liquid scintillation samples containing 3H, 14C and 36Cl are described. An off-line desk computer was used for data processing. Quench correction was made with the external standard channels ratio method.

Comptage direct des echantillons Plasmatiques en Scintillation Liquide par Etalonnage Interne-Externe

A direct incorporation method for liquid scintillation counting of plasma samples is described. after dilution in saline, the plasma samples are mixed with a new scintillator emulsifiying mixture (“Scintingel”). Counting efficiency is obtained by a pseudo-internal method. Results show great significance of plasma quenching particularly in the field of clinical studies. Quench correction curves for tritium, sulphur-35 and calcium-45 are plotted using counting efficiency versus external standard channel ratio. The sample activity in dpm is given with a 5 per cent precision.

A pitfall in the use of polyethylene vials in liquid scintillation counting

It has been shown that there is a migration of toluene through the walls of polyethylene vials, which are frequently used in liquid scintillation counting (1,2). It seems reasonable to assume that scintillators migrate in a similar way. Mueller (3) reported a continuous drift of the external standard channel ratio when using polyethylene vials. It is proposed in the present study that this drift is due to the migration of the scintillators into the walls of the vials. All the chemicals used were of reagent or scintillation grade. Samples were counted in a Nuclear-Chicago Mark II or a Packard 3375 liquid scintillation counter at 4°C. The pulse-height spectra of the external standards (133Ba and 226Ra + 241Am, respectively) were obtained at the recommended gains for 3H and l*C by stepwise manual movement of a narrow channel, which was 5% of the maximum energy range used. W ith glass vials there were no changes in the spectra obtained from the external st.andards during a 5 day period. W ith polyethylene vials, however, there was an increase of the count rate in the low-energy part of the spectrum when using the recommended 14C gain (Fig. 1). When the 3H gain was used, the additional counts appeared in the low-energy half of the spectrum. After the vials were emptied and washed once with toluene, they still yielded counts in the low-energy part of the spectrum. “Old” scintillator solution transferred into “new” vials showed a normal spectrum. “New” scintillator solution in “old” vials showed an increased count rate in the low-energy part of the spectrum. The count rate in the low-energy part of the spectrum (‘“C gain) gradually increased after the scintillator solution was added to the vial (Fig. 2). The count rate in the integral channel increased by about 1% during a 5 hr period. This increase was fairly similar to that found in the low-energy part of spectrum. Similar results were obtained in both liquid scintillation counters used and with the two scintillator solutions used and also with polyethylene vials of different quality.

Use of Aquasol scintillator micture for liquid scintillation counting of beta radioactivity in biological tissue

The preparation of biological tissues for liquid scintillation counting, by ultrasonic disruption, decoloration with hydrogen peroxide, and solubilization in Aquasol ® scintillation fluor, has been described. The high tissue-dependent background counts recorded at 25°C were found to decrease to satisfactory levels by cooling and assaying at 2°C. The isotope channels ratio method was found to be a suitable means of quench correction for both tritium and 14C. External standard channels ratio quench correction was considerd to be unsuitable under these experimental conditions for both tritium and 14C. Maximum counting efficiencies for tritium and 14C were 19·5 and 80·4 per cent respectively. Up to 598 mg of tissue, 186 mg of feces and 1·13 ml of urine were radio-assayed using this method.

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.

Counting quenched liquid scintillation samples using an outside-the-instrument gamma source and an external standard channels ratio method

An external standard channels ratio method which can use a gamma source outside the spectrometer has been developed. The calibration procedure for a 2 mCi Cs 137 source is described. The relationship between counting efficiency and the external standard channels ratio is represented by a cubic or quadratic equation fitted by least squares. Once the calibration for a source is established, the same source settings can be used for counting any isotope. Calibration curves which cover a wide quenching range have obtained for H 3, C 14, and Cl 36 samples quenched with chloroform and methyl red. The average dpm determined by this method for some miscellaneous quenched carbon-14 labeled samples had standard deviations less than ±2.5% for replicate samples. The differences between the calculated and supplied dpm of these samples were also less than ±2.5%.

Liquid scintillation counting: Determination of background counts of quenched samples using an external standard channels ratio

A Cs-137, 2 mc, external standard has been used to study the effect of quenching and sample volume on background counts. Background calibration curves in which the external standard ratio is plotted against the background counts have been prepared for methyl red, a color quenching agent, and chloroform, a chemical quenching agent. Using these curves, the background counts of some quenched test samples have been estimated to within 5% of the actual background. The reproducibility of the external standard ratios and of the background counts of replicate quenched and unquenched samples, and empty vials, has been determined. For replicate samples (5–13) the standard deviation for the external source ratio is smaller than ±1.0% and for the background counts smaller than 5.0%.