Simultaneous determination of35S and14C in double-labelled organic compounds by liquid scintillation counting

An isotope analytical method for the simultaneous determination of³⁵S and¹⁴C in double-labelled organic compounds by liquid scintillation counting is described. The sample is burned in a stream of oxygen. Sulfur oxides are converted to sulfuric acid and separated from other combustion products, including carbon-14 dioxide, on a heated quartz wool column previously wetted with hydrogen peroxide. Carbon dioxide is collected from the gas stream by an absorbent suitable for liquid scintillation counting. The residual sulfuric acid is rinsed off the column with water and the aqueous solution obtained is mixed with a liquid scintillation cocktail for radioactivity measurement. The final solutions ready for counting are obtained in less than fifteen minutes, quantitative collection recovery is achieved and no cross contamination occurs.     

A semi-automatic combustion method for the simultaneous determination of3H and35S in doubly labelled organic materials by liquid scintillation counting

A sample preparation method developed for the simultaneous liquid scintillation assay of tritium and³⁵S in doubly labelled organic materials is described. The sample is burnt in a stream of oxygen and the radioactive isotope carriers formed are collected separately for individual counting.³⁵S content of the sample is measured as a dilute sulfuric acid solution, while the tritium is counted as water. The procedure is free of cross-contamination and memory effect, provides quantitative analytical recovery, and the final solutions ready for counting are obtained in twelve minutes.     

Mikrobestimmung von Kohlenstoff und Wasserstoff,sowie von 14C,Tritium und Deuterium im Stickstoffstrom

A microanalytical method for the determination of carbon and hydrogen is described. The procedure involves the combustion of the organic substance in a stream of nitrogen and the oxidation of the decomposition products with oxygen. Halogens and sulphur are absorbed by the combustion catalyst (according to Körbl), whereas nitrogen oxides are reduced on a copper surface. The combustion products, CO₂ and H₂O are determined gravimetrically; in the case of radioactive samples they are appropriately absorbed and counted in a liquid scintillation counter. Strongly quenching singly and doubly labelled samples, which cannot be accurately counted even by modification of the counting device, give equally high radioactive yields (75% for ¹⁴C, 30% for ³H), since counting is not influenced by other gaseous impurities. Deuterium is quantitatively determined by measuring the intensity of the OD-signal at 2500 cm^?1 with an infrared spectrometer.     

Rapid determination of tritium and carbon-14 in urine samples using a combustion technique

Traditionally in bioassay monitoring, ³H determinations in urine have been performed using either direct counting (with or without sample decolourisation) or distillation whilst ¹⁴C has been determined on separate sub-samples following chemical isolation of the carbon from samples. Although these techniques are relatively straightforward they do not permit simultaneous determination of ³H/¹⁴C. For ³H, direct counting can be significantly affected by variations in sample composition/colour resulting in varying degrees of sample quench, does not distinguish between aqueous/organically-bound ³H and is limited to small sample sizes. This study describes the use of purpose built multi-tube combustion furnace for the simultaneous extraction and determination of ³H and ¹⁴C. The technique is insensitive to sample composition and can be adapted to measure Tritiated water (HTO) and organically bound tritium separately. The development of a multi-tube system with integrated cool-down facility permits rapid throughput of high sample numbers and has been proven effective in decommissioning waste characterisation. In addition, the furnace-based technique is capable of processing larger sample sizes, increasing analytical sensitivity and accuracy of dose assessment.     

Automatic isotope gas analysis of tritium labelled organic materials

An isotope analytical procedure and an automatic instrument developed for the determination of tritium in organic compounds and biological materials by internal gas counting are described. The sample is burnt in a stream of oxygen and the combustion products including water vapour carrying the tritium are led onto a column of molecular sieve-5A heated to 550 °C. Tritium is retained temporarily on the column, then transferred into a stream of hydrogen by isotope exchange. After addition of butane, the tritiated hydrogen is led into an internal detector and enclosed there for radioactivity measurement. The procedure, providing quantitative recovery, is completed in five minutes. It is free of memory effect and suitable for the determination of tritium in a wide range of organic compounds and samples of biological origin.     

Instrumentelle Kompensation des Quencheffektes bei der Bestimmung von 14C und 35S

Zusammenfassung Ein Quencheffekt tritt auch nach Oxydation der organischen Probe auf. Dieser ist bedingt durch gewisse Verbrennungsprodukte, wie NO₂, Halogene, SO₂ und SO₃. Es wurde gefunden, da\ man den Quencheffekt der Verbrennungsprodukte bei der Bestimmung von ¹⁴C und ³⁵S ausschalten kann, wenn man die Spannung des Data-Photomultipliers bis zu einem gewissen Punkt (Kompensationspunkt) erhöht und die Messung in einem ZÄhlfenster durchführt. Der Kompensationspunkt wird graphisch ermittelt; hierzu mi\t man die ZÄhlrate des reinen Absorbens sowie die ZÄhlrate des Absorbens, das die maximal zu erwartende Menge Verbrennungsprodukt enthÄlt, bei verschiedenen Data-Spannungen. Der Zusammenhang zwischen der instrumenteilen Kompensation und dem Energiespektrum von ¹⁴C wird aufgezeigt. Bei der Bestimmung von Tritium lÄ\t sich der Quencheffekt nicht kompensieren, denn das Energiespektrum von Tritium wird durch eine Quenchverbindung anders beeinflu\t als das Spektrum von ¹⁴C bzw. ³⁵S.

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Summary After combustion of the organic sample a quenching effect is observed, due to several combustion products as NO₂, halogens, SO₂, and SO₃. We found, that it is possible to eliminate quenching of the combustion products in the determination of ¹⁴C and ³⁵S, if the high voltage of the data-photomultiplier is raised to a certain level (compensation point) and if the counting is performed in a window. The compensation point is calculated graphically by determining the counting rate of the pure absorbant and the absorbant plus the highest expected amount of combustion products. The relation between instrumental compensation and the energy spectrum of ¹⁴C is elucidated. It is not possible to compensate quenching in the determination of tritium, because the energy spectrum of ³H is influenced in a different way than the spectrum of ¹⁴C and ³⁵S.

     

Recent progress and application of low level liquid scintillation counting

The use of an ultra low level liquid scintillation counter with extremely low background, MCA technique, storage and software evaluation of pulse height spectra has given very low LLD's, the possibility of - and -spectrometry to some extent and time saving optimization of counting conditions. Quick and very simple but yet accurate analytical methods could be worked out worked out for environmental measurements: Environmental levels of tritium,¹⁴C in several assimilation products,²²²Rn and²²⁶Ra in water without any sample pretreatment. Suggestions for possible further applications in environmenial monitoring and low level counting are given.     

Mikrobestimmung von Kohlenstoff und Wasserstoff, sowie von 14C, Tritium und Deuterium im Stickstoffstrom

Zusammenfassung Eine mikroanalytische Kohlenstoff-Wasserstoffbestimmung wird beschrieben, bei der die organische Substanz im Stickstoffstrom verbrannt und deren Crackprodukte mit Sauerstoff oxydiert werden. Halogene und Schwefel werden vom Verbrennungskatalysator (nach Körbl) absorbiert, während eventuell entstandene Stickoxide an einer Kupferschicht zur Reduktion gelangen. Die entstandenen Verbrennungsprodukte CO₂ und H₂O können gravimetrisch erfaßt oder bei radioaktiven Proben durch entsprechende Absorptionsmöglichkeiten in einem Flüssigkeits-Szintillationszähler zur Zählung gebracht werden.Stark quenchende einfache, sowie doppelt markierte Proben, die man auch durch Modifikationen des Zählgeräts nicht mehr genau auszählen kann, können mit gleich hoher Zählausbeute wie nichtquenchende erfaßt werden (75% für ¹⁴C und 30% für ³H), da keine störenden Fremdgase die Zählung beeinflussen.Deuterium wird durch Ausmessen der OD-Bande bei 2500 cm^–1 mit einem Infrarot-Spektrometer quantitativ bestimmt.

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Microanalytical determination of carbon and hydrogen, ¹⁴C, tritium and deuterium in a stream of nitrogen

A microanalytical method for the determination of carbon and hydrogen is described. The procedure involves the combustion of the organic substance in a stream of nitrogen and the oxidation of the decomposition products with oxygen. Halogens and sulphur are absorbed by the combustion catalyst (according to Körbl), whereas nitrogen oxides are reduced on a copper surface. The combustion products, CO₂ and H₂O are determined gravimetrically; in the case of radioactive samples they are appropriately absorbed and counted in a liquid scintillation counter. Strongly quenching singly and doubly labelled samples, which cannot be accurately counted even by modification of the counting device, give equally high radioactive yields (75% for ¹⁴C, 30% for ³H), since counting is not influenced by other gaseous impurities. Deuterium is quantitatively determined by measuring the intensity of the OD-signal at 2500 cm^–1 with an infrared spectrometer.

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Herrn Prof. Dr. H. Schmid bin ich für das wohlwollende Verständnis meinen Arbeiten gegenüber zu bestem Dank verpflichtet. Sämtliche Glas- und Quarzgeräte wurden in der Glasbläserei unserer Institute von Herrn B. Thueler angefertigt, wofür ich auch ihm an dieser Stelle danken möchte.     

A novel method for the simultaneous determination of125I and14C activities using liquid scintillation counting

The viability of a dual label liquid scintillation technique has been investigated. To avoid the need for two procedures, gamma counting for¹²⁵Iodine (¹²⁵I) and liquid scintillation counting for¹⁴C. Since the¹²⁵I spectrum covers almost as wide a range of pulse heights as¹⁴C, conventional dual label methods would result in very low¹⁴C counting efficiencies. The conventional dual label technique has ben modified to increase the¹⁴C counting efficiency and to accomodate the consequent additional spillover of¹²⁵I counts into the upper window. This dual label technique has been applied to the determination of¹²⁵I and¹⁴C activities in blood samples. The accuracy of the method has been tested, and its advantages and limitations are discussed.     

Temperature dependence of pulse-height distribution in liquid scintillator

The differential pulse-height distributions for²⁴¹Am,^131mXe,¹⁴C and³H are investigated as a function of temperature. The spectra are shifted toward higher pulseheights with decreasing temperature. During the measurement, the temperature of photomultipliers of liquid scintillation system are kept at 8.8 °C. The counting efficiency of¹⁴C and³H increases with decreasing temperature. The mechanism involved in this effect is discussed.     

Vergleich der Meßgenauigkeit der Szintillations-Zählung 3H- und/oder 14C-markierter Proben durch externe bzw. interne Standardisierung und Anwendung auf die Sauerstoff-Kolben-Verbrennung

After oxygen flask combustion scintillation samples often show an increase in counting rates for several hours. Even after such a time identically prepared samples are statistically significantly more different as one should expect by weighing and pipetting errors. The inconstant cpm values during the first hours and the differences between the samples can mostly be eliminated by quench correction curves (dependence of counting efficiency and external channel ratio upon oxygen concentration). The dpm values achieved according to this method show smaller standard deviations than by internal standardisation. The procedure of the external standardisation was examined for error propagation. A system of toluene/methanol/phenethylamine absorbs carbon dioxide and water quantitatively. With this mixture the following counting efficiencies are achieved: 25% for ³H, 85% for ¹⁴C and for samples containing ³H and ¹⁴C 15% for ³H and 10% for ¹⁴C if the ³H channel is adjusted according to Klein and Eisler.     

Flow-through radioactivity detection of 3H- and 14C-labelled compounds in reversed-phase liquid chromatography by a liquid scintillation counting technique based on post-column extraction

A method for flow-through liquid scintillation counting in reversed-phase liquid chromatography (RP-LC) based on the continuous extraction of aqueous column eluates with a water-immiscible liquid scintillator is evaluated in terms of sensitivity, reproducibility and extra-column band broadening. ³H- and ¹⁴C-labelled phenylthiohydantoinamino acid derivatives of widely different polarity serve as model compounds. For extractable derivatives, counting efficiencies of over 30 and 80% can be obtained for ³H and ¹⁴C, respectively. The reproducibility and extra-column band broadening depend on the mixing ratio of scintillator and LC eluent; relative standard deviations (peak areas) of less than 3% can be obtained. The sensitivity of flow-through counting can be increased at least 150-fold by storing the segmented scintillator/eluate stream in a capillary storage loop. After the separation is complete, the stream is re-introduced into the radioactivity detector at reduced flow-rates to increase the mean residence time, i.e., the counting time, in the detector.     

Autoradiographical detection of tritium and14C-ethylene on nickel sheet

The detection of tritium and¹⁴C-ethylene on the surface of nickel sheet was carried out by means of autoradiography. Two autoradiographical methods were used, the ordinary stripping-film method and the electron-microscope autoradiographical method. The ordinary autoradiographs indicated that¹⁴C-ethylene accumulates at scratches on the surface of the sheet; however, tritium accumulates at grain boundaries and scratches. Electron-microscope autoradiographs indicated that tritium accumulates on the step-edges of slip band of nickel.     

Possibilities of the determination of3H,14C and131I individually and in mixtures,by the method of amplitude attenuation using liquid scintillators

Possibilities of the determination by radioactivity measurements of³H,¹⁴C and¹³¹I are described for the individual nuclides and their mixtures, with the use of liquid scintillators. The changes in the counting efficiency have been determined as a function of the parameters of the measuring equipment, and parameters are suggested which make possible the determination of³H,¹⁴C and¹³¹I individually, or in the pairs³H−¹⁴C,³H−¹³¹I,¹⁴C−¹³¹I, and finally, in the triplet³H−¹⁴C−¹³¹I.     

A spectral overlap method for self monitoring quench correction in double isotope liquid scintillation counting

A method for quench correction of samples with double radioactive labelling is described. Each nuclide makes a contribution to the counting rate of three channels of a liquid scintillation counter. This channel overlap is an essential requirement of the calibration procedure rather than a limitation, and allows more freedom in the choice of counting conditions. After calibration with suitable standards the method will tolerate wide variations in the ratio of one isotope to the other extending to single label samples of either isotope. This is the outstanding advantage over the channel ratio method which requires a statistically significant counting rate for the higher energy isotope. The method takes advantage of the facilities offered by a computer which may be on line or remote.¹⁴C and tritium are used to demonstrate the utility of the method.     

Liquid scintillation assay of 3H and 14C-labelled polymers

The assay of a range of ³H and ¹⁴C-labelled polymers by liquid scintillation counting is reported. Methods of sample preparation such as combustion, solution, gelation and suspension techniques are described and compared. The validity of a variety of procedures of counting efficiency determination for the above methods is examined and critically discussed.     

Synthesis of doubly labeled polyacrylic acid with14C and3H

Polyacrylic hydrogels were¹⁴C- and³H-labeled in three main steps. In the first one, the monomer as sodium salt was¹⁴C-labeled at the carboxyl group via the carbonation of vinylmagnesium bromide and [1-¹⁴C]acrylic acid was obtained, followed by labeling with tritium via isotopic exchange in heterogeneous catalysis. The monomer was purified and its radiochemical purity was analyzed using TLC. In the last step, the hydrogel was obtained through radiopolymerization of the doubly labeled monomer using a⁶⁰Co source. The oligomers and unpolymerized monomers were eliminated from the hydrogel by swelling in water followed by dehydration with methanol.     

Sample treatment techniques for the determination of environmental radiocarbon in a nuclear power station area

This report describes the environmental sample treatment techniques for¹⁴C measurement with liquid scintillation counter. The groundwater sample of about 80 liters was collected from well and inorganic carbon was removed by acidification and recirculated gas stripping with the extraction efficiency of more than 98%. The biological samples were freeze-dried and combusted to carbon dioxide in high pressure combustion unit with a combustion efficiency of nearly 99%. The¹⁴CO₂ in the stack effluents was collected by an air bubbler with a collection efficiency of more than 99% for a sampling time of two weeks. Sampling of¹⁴C in reduced form also has been done by passing the gases through a tube furnace with Pt/Al and Pd/Al catalyst. Active and passive sampling methods for atmospheric¹⁴C measurements were compared in detail, and it could be concluded that the uncertainty associated with passive sampling method was quite acceptable for environmental monitoring. The CO₂ trapped in NaOH was precipitated as BaCO₃, and subsequently reconverted to CO₂ for environmental samples and transferred to Carbo-Sorb E^TM for liquid scintillation counting. In case higher precision is the deciding factor, benzene synthesis would be employed with home-made benzene synthesizer.     

Tritium assay of labelled organic compounds by the flow monitoring counter

Summary A sensitive, simple and cheap counting system for the radioactivity assay of tritiated organic compounds is described. The organic labelled material was converted into carbon dioxide and tritiated hydrogen in an ignition-reduction quartz tube filled with copper oxide and iron fillings. Tritiated hydrogen was then assayed while passing through a flow monitoring counter described earlier [1]. Application of the described counting system greatly decreased the analysis time as compared with other techniques in which internal filling gas counters were used. Results showed that the counting system could readily measure activities as low as fractions of a nCi per mg of tritiated organic compound. The counting system could be used for the assay of organic compounds doubly labelled with tritium and carbon-14.

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Zusammenfassung Eine empfindliche, einfache und nicht kostspielige ZÄhlvorrichtung zur AktivitÄtsbestimmung tritierter organischer Verbindungen wird beschrieben. Die markierte organische Substanz wird durch Erhitzen in einem mit Kupferoxid und EisenspÄnen gefüllten Quarzrohr zu CO₂ und tritiertem Wasserstoff umgesetzt, der durch einen bereits früher [1] beschriebenen Durchflu\zÄhler geleitet wird. Im Vergleich zu anderen Methoden kann mit der empfohlenen Vorrichtung die Analysenzeit betrÄchtlich herabgesetzt werden. Bruchteile von 1 nCi/mg können noch gemessen werden. Das Verfahren ist auch für doppelt markierte (³H,¹⁴C) organische Verbindungen brauchbar.

     

Automatic sample preparation of35S labelled organic compounds for liquid scintillation counting

An automatic sample preparation method for the determination of³⁵S in organic compounds by liquid scintillation counting is described. The sample is burned in a stream of oxygen and the combustion products are led onto a quartz wool column wetted with dilute hydrogen peroxide. Sulfur oxides are retained on the quartz wool as sulfuric acid, while the other acid producing combustion products are eliminated by evaporation. The residual sulfuric acid in rinsed with distilled water, the sulfuric acid solution obtained is added to a liquid scintillation cocktail and the radioactivity is measured with a liquid scintillation counter. The combustion-evaporation process runs automatically according to the operational program carried out by an electronic programmer.