DK143373B - MICELLAR MEDIUM FOR LIQUID SCINTILLATION SCREEN - Google Patents

Description

I® (12) PUBLICATION <n) 143373 B

(19) DENMARK

PATENT DIRECTORATE. AND THE TRADE BRAND

(21) Application No. 383/68 (51) irrt.CI.3 8 01 T 1/204 (22) Submission day 31 · Jan · 1968 (24) Race day 31 · Jan. 1968 (41) Aim. available Aug. 2 1968 (44) Presented 10 Aug. 1981 (86) International Application No. - (86) International Filing Day - (85) Continuation Day - (62) Master Application No. -

(30) Priority 1 Feb 196 ?, 613109, US

(71) Applicant EDWIN ANDREW SENA, Littleton, US: CHESTER LOUIS STJTULA, Elk = hard, US: BERT MILLS TOLBERT, Bethesda, US.

(72) Inventor Same.

(74) The Hofman-Bang & Bout ard patent office.

(54) Mieellar medium for fluid = scintillation count.

The invention relates to a micellar medium for liquid scintillation counting of the kind set forth in the preamble of claim 1.

The measurement of isotope radiation is different according to the type of radiation. Hard radiation, such as gamma radiation penetrating opaque materials, is readily measured directly on a wide variety of detection means. Counting the softer radiation normally used in humans and other animals is often quite difficult. Eg. water strangles the radiation of tritium. Since water is part of living organisms, this creates many problems. As a result, procedures have been developed for counting such radiation in the absence of water and even a few methods for counting in the presence of water.

For example, dissolution systems are described for liquid scintillation counting, wherein the materials whose radioactivity is to be determined are brought into alcoholic solution by complexing with "Hyamine" [trade name for p- (diisobutyleresoxyethoxyethyl) dimethylbenzylammonium hydroxide] or related quaternary ammonium compounds. . Solution systems have also been described in which the materials to be counted are brought into solution with mixed solvents selected from, for example, toluene, naphthalene, water, 2,5-diphenyloxazole (PPO), 2,2'-phenylene bis ( 5-phenyloxazole) (POPOP), 2-ethoxy ethanol ("Carbitol") and diethylene glycol monoethyl ether and derivatives thereof ("Cellosolves"). However, such resolution systems have only limited applications.

Patterson et al., Anal. Chem., Vol. 37 (1965), p. 856, describe the measurement of low-energy beta-radiators in aqueous solution by liquid scintillation counting of emulsions. Specifically, they describe the use of stable emulsions of water and toluene formed by the surfactant "Triton-X 100" [trade name for an isoethyl ether of a polyethylene glycol]. These are actual emulsions, and there is nowhere the formation of thermodynamically stable micellar systems. Such emulsions are extremely complex and involve the risk of serious errors in tritium measurement (R.H. Benson, Anal. Chem., Vol. 38, No. 10 (1966), pages 1353-1356).

W. C. Tosch, Anal, Chem., Vol. J7, 959 (June 1965), found that transparent emulsions were useful in uniformly dispersed aqueous solutions containing gamma-ray trace elements.

Tosch believed that systems of the type described could prove useful in liquid scintillation work with low energy sources.

But experiments have shown that transparent emulsions of the type used by Tosch are not suitable for counting radiation from low-energy sources such as tritium, even when the usual primary and secondary scintillators and scintillation solvents are incorporated into the systems. In experiments, the chemical extinction and chemiluminescence were quite pronounced, sometimes to such an extent that the desired radiation could not be detected. Other problems associated with emulsion counting also continued to exist.

3 143373

The composition of micellar systems, also called microemusions, transparent emulsions or colloidal solutions, and various uses thereof are known. For example, U.S. Patent No. 3,282,843 discloses emulsifiers comprising micellar systems with a combination of non-sulfur-containing surfactants for various industrial applications, and U.S. Patent Nos. 2,953,530 and 3,028,338 relate to the use of micellar systems in agents for detection of surface irregularities and cracks.

The invention provides that thermodynamically stable micellar systems can be used to prepare liquid scintillation counting media which provide high counting efficiency and show little or no chemiluminescence, quenching or phosphorescence under counting conditions.

This is achieved by the fact that the medium according to the invention is peculiar to the characterizing part of claim 1.

The thermodynamically stable micellar systems used according to the invention are made of several surfactants with substantially different properties, Tselling media produced therefrom provide high counting efficiency and exhibit little or no chemiluminescence, quenching or phosphorescence under counting conditions. These systems differ from the prior art solubilizers in that the known emulsion systems, by vapor phase and NMR examination, contain a substantial mass of liquid as the internal phase. The inner phase of the two-phase micellar systems and the composite counting media have less vapor pressure than the liquid mass. NMR studies also show the absence of any significant fluid mass as the dispersion phase. The micellar systems used according to the invention, which may also be single-phase, contain surfactants without amines having one or more hydrogen atoms, sulfonates, sulfonic acids with substantial conjugation, ketones or quaternary compounds.

Preferably, the medium according to the invention, as part of the basic combination or in addition, contains a so-called cooperative surfactant (cosurfactant) which stabilizes micelles, for example a surfactant with less molecular size or other molecular polarity which apparently fills the gaps between the surfactant molecules at the micelle interface, or a powder which stabilizes the micelles by electrostatic forces.

The degree of improvement achieved with the media of the invention in comparison with a medium based on a transparent emulsion containing a sulfonate is significant as shown in the specific examples.

Although the micellar system is often nothing more than a mixture of one or more surfactants and one or more interacting surfactants, the formulated medium contains, in addition to the micellar base system, one or more scintillation solvents, primary scintillators and optionally secondary scintillators. The micellar system and the formulated medium will solubilize a liquid or soluble radioactive sample to at least half and preferably at least as much volume as the original micellar system present without forming a transparent thermodynamically unstable dispersion containing dispersed free sample material. . Thermodynamically unstable dispersions are those which will not repeatedly restore a stable dispersion after breaking the dispersion by temperature change or which break with time.

The surfactants, the interacting surfactants, and all basic solvents, i.e. those required to solvate isotope assay, surfactant, etc., used in accordance with the invention are substantially inactive in chemical energy transfer resulting in chemiluminescence, fluorescence or phosphorescence. Furthermore, all medium components are liquid in the sample containing medium under counting conditions. Basic solvents which can be used to formulate the micellar systems can be both polar and non-polar. Water is the preferred polar base solvent, while low molecular weight alkanes, alkenes without significant conjugation, uncondensed aromatic compounds, etc., are preferred non-polar solvents. The use of non-polar base solvents is preferred where a solvent is used.

5 143373

The micellar systems used for composition of the media of the invention; recalls the mixtures of surfactants used in the composition of "soluble oils" and "microemulsions" in the art of chemical purification, cutting oils, etc. The methods which can be used for the composition of the micellar systems are those which are used for the composition of the known surfactant systems for use in the formation of emulsions, and include e.g. the technique known as the hydrophilic-lipophilic balancing method for the composition of emulsions.

Many surfactants can be used alone or in combination for the composition of the micellar systems and media of the invention. However, since the compositional technique common to the field of emulsions and soluble oils is used, the same problems encountered in the preparation of emulsions also arise, for example, cationic and anionic surfactants are not generally useful in combination. Careful empirical experiments are required to compile optimal micellar systems and media from given combinations of surfactants and interacting surfactants. Several surfactants are used in the composition, and most advantageously, one of the surfactants is oil-soluble and another water-soluble. The person skilled in the art will know the tests necessary to determine the utility of new materials, e.g. scintillation solvents, surfactants, etc.

Many surfactants find use in the media of the invention. Among these are fatty acid soaps and alcohols, polyethoxy ethanols, alkyl succinates, ethylene oxide propylene oxide condensates, etc. More particularly, within these groups include sodium umlinoleat, linoleic acid, stearic acid, potassium oleate, glycerolectopalmitat, lauryl alcohol, dodecyl alcohol, octadecyl stearate, glycerol monostearate, morpholine, sorbitan trioleate, polyoxyethylensorbitolhexastearat, propylene glycol monostearate, sorbitan sesquioleate, polyoxyethylene-tol-4,5-oleate, diethylenglycolmonooleat, polyoxyethylendioleat , polyoxypropylene mannitol dioleate, polyoxyethylene oxypropylene oleate, tetraethylene glycol monolaurate, polyoxyethylene lauryl ether, polyoxyethylene acetyl ether, isooctylphenol polyethoxyethanol, dihexylsulfosuccinate.

In general, surfactants containing amino groups having one or more hydrogen atoms, sulfonates, sulfonic acids, ketones and quaternary compounds (under basic or substantially neutral conditions) cannot be recommended for use in the media of the invention, as they often severely deplete the emissions. , which is analyzed. These phenomena are not fully understood, but definitely exist as shown in the specific examples of sulfonate surfactants.

Among co-surfactants used to form the micellar media are low molecular weight alcohols, ethers and esters. Again, amines, ketones, etc. not desirable.

The usual scintillators, both primary and secondary, can be used to make the micellar systems. 2,5-diphenyloxazole (PPO) is the preferred scintillator, while 2,2'-phenylene-bis- (5-phenyloxazole) (POPOP) is the preferred secondary scintillator. Other scintillators may also be used. These include, for example, p-terphenyl, 2,2'-phenylene-bis- [5- (methylphenyl) oxazole] (dimethyl-POPOP), diphenylhexatriene, 2- (a-naphthyl) -5-phenyloxazole (a -NPO) and 2,2'-phenylene-bis- [5- (a-naphthyl) oxazole] (a-NOPON). Scinillation solvents which may be used in accordance with the invention are well known in the art of liquid scintillation counting and include, for example, toluene, xylene, naphthalene, β-cymene and dioxane.

The following examples serve to illustrate the invention. EXAMPLE 1

A system containing by weight 25> 1% tall oil fatty acids, 24.2% n-hexanol, 15.8% isopropanol, 22.1% isooctylphenol polyethoxyethanol and 12.8% aqueous solution of HaOH (25%) is prepared. ). 10 ml of this micellar system is added to ten ml of toluene containing 7 g / l PPO and 0.36 g / l POPOP to prepare a medium.

This medium will tolerate moderate amounts of inorganic acids and limited amounts of alkali. Ted addition of the sample, the system usually becomes clear immediately. If the amount of aqueous solution is close to the maximum for the amount of micellar system used, the clarification takes place more slowly and additional micellar system must be added. If, by the addition of additional micellar system, a satisfactory counting system is not obtained, the sample is diluted where necessary or a smaller amount of aqueous solution is used to prepare a new counting solution. Strong acids can be neutralized with sodium hydroxide and bases with additional tall oil fatty acids or with the mixture of Example 2. Preferably, the pH of the sample-containing medium to be determined is approx. 7. If it is necessary to count samples containing dissolved CQg, add small amounts (0.5 ml) of distilled ethanolamine to the medium.

EXAMPLE 2

This medium is designed as an acidic solubilizer for alkaline tissue solutions or another highly alkaline sample. It contains by weight 28.7% tall oil fatty acids, 27.8% n-hexanol, 18.2% isopropanol and 25.3% isooethylphenol polyethoxyethanol. This millionaire system is added to the same amounts of the toluene fluoxescent used in Example 1. Materials to be tested, such as> 0 mg wet tissue, are placed in an oven at 80 ° C for 1 hour or until clear , and is thus dissolved in 2 ml of 2ET NaOH, which are all added to the medium to be counted. This system will not constitute a satisfactory counting system unless neutralized. Again, the maximum count pH is approx. 7 as determined with pH paper.

If the amount of organic matter is large, a clear solution may not form. The medium must then be supplemented with small amounts of the medium of Example 1 in the ratio of 2 ml of the medium of Example 1 to 10 ml of toluene.

EXAMPLE · 3

Go. Weigh 50 mg of hemoglobin in a liquid scintillation vial. 1 ml of 2 H NaOH is added to the hemoglobin and the sample is heated in an oven to ca. 80 ° C for 1 hour and cool, approx. 50 mg of la 2 O 2 is added to remove the color. The medium of Example 2 is added in a slight excess to neutralize the alkali from Ua2O2 on which is counted. Serious suppression can be encountered in the systems thus treated, although counting and% is possible.

The alkaline solution technique of this example followed by neutralization and solubilization with the medium of Example 2 is applicable to counting a wide variety of insoluble substances, e.g. old urine, which contains relatively large amounts of precipitated protein, can also be used to solubilize tendons, cellulose materials, dried and decomposed tissues, synthetic polymers, etc. 2 ml of the medium of Example 2 will normally solubilize approx. 25 mg of pure, dried protein.

EXAMPLE 4

A normal medium is prepared by weight 37.9% sodium dihexyl sulfosuccinate, 4 »8 ° isopropanol, 4» 7 # water and 52.6 $ isooctylphenol polyethoxyethanol. This micellar system forms a medium with a slightly higher tolerance to salts than the medium of Example 1 and also a lower natural radiation background. 2 times the volume of aqueous sample to be counted. This medium works well in counting uranyl salt solutions. The micellar system is added to the toluene fluorescent of Example 1 at a ratio of 1: 2: 10.

EXAMPLE 5 Label I shows typical results in several counting situations with tritium-labeled compounds. All counting vials contained 12 ml of the toluene fluorescent mixture and 3 ml of the micellar system of Examples 1 or 4. Unless otherwise indicated, the toluene fluorescent solution contained 7 g / l PPO and 0.36 g / ml. 1 POPOP. The efficiencies were determined by the international standard method using a Beckman liquid scintillation spectrometer with a ROA photomultiplier tube.

TABLE · I

Counting efficiency of some tritium-labeled compounds in media of the invention

Solubilized Substance_ Quantity_Effectivity

Tooth with added tritiated water 0.1 ml 42 ^ 0.2 ml 39 1.0 ml 37 2.0 ml 32

Toluene (3H) (alone) -— 55

Toluene (1 H) with water 1.0 ml (water) 49 9 143373

Solubilised substance_ Quantity _ Efficiency% -labelled urine 0.5 ml 41 1.0 ml 57

Ascorbic acid (¾) (aqueous solution) 1.0 ml 45

Blood plasma labeled with 1.0 ml of 30

Water added to tritiated water (o-xylene-PED as fluorescent) 0.2 ml 44 0.7 ml 39 1.0 ml 35 - ........ - - I .....'------ EXAMPLE &

Carbon-14 can be counted by approx. 80-90 $> efficiency using the media of Example 4. A counting solution added - 50-labeled toluene gave an efficiency of 89 when anhydrous or in cold 1 ml of added water, 87 efficiency was obtained in a medium formulated with the micellar system of Example 1 and containing 1 ml of aqueous fructose (for 1 $) solution. 87 # efficiency was obtained with the medium of Example 1 containing 1 ml of aqueous glycine 1Ζ | Ό in 1 # solution.

EXAMPLE 7 - Fe was counted by approx. 30 µm efficiency, 10 ml of a ^ Fe-labeled saline solution containing about 22,000 parts per million total dissolved solids was dispersed in a medium formulated with the micellar system of Example 4.

EXAMPLE 8 3 C1 was counted at approx. 100% efficiency when 1 ml of a - * ® C1-labeled isotonic physiological saline sample was dispersed in a medium formulated using the micellar system of Example 4.

EXAMPLE 9 Co was counted at 100 $ efficiency (β-irradiation was tested).

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trolled), about 1 ml of a Co-labeled aqueous solution of OoClg was solubilized in a medium formulated with the micellar system of Example 4. In general, efficiencies of approximately 100 f> can be expected for radioisotopes with maximum β-irradiation energies of a few hundred keY or above.

• RvsniMPEIi 10

A toluene fluorescent of 6 g of PPO was prepared in 1 liter of toluene, the loluene fluorescent (25 g) was then mixed with 25 g of each of the surfactant sulfonate agents A, B and C. A is "Petronate KH (a highly purified petroleum sulfonate). B is "Shell Sac" (a petroleum sulfonate from Shell Chemical Company which was vacuum evaporated to remove the oil medium; this material was approximately 100 fo active). C is "Shell" Db. 65413 Dot Bo. S-65-148 petroleum sulfonate with an analysis of about 62 fo active sulfonate. 15 ml of the toluene fluorescent was then added to 1, 2 and 3 ml samples of each of the three surfactant fluorescents described above. A control of 15 ml of toluene fluorescent was used in each case.

The samples were placed in a Beckman liquid scintillation system without the addition of radioactive sample to obtain background count values. The samples were then counted repeatedly until an approximately constant count rate was observed from all samples. Initial values of 24,609.0, 37,294.0 and 49,987.0 were observed for 1, -2, and 3 ml solutions of the surfactant A. respectively. At 60 minutes, count values were 2,093.0, 5,096r0 and 7,866.0. Initial values for surfactant B systems were 34 578.0, 40 687.0 and 48 686.0, respectively. 60 minutes were 3,239.0, 5,510, 0 and 7,259.0, respectively. The initial values for samples containing the surface active agent C were 32,305.0, 46,595.0 and 34,353.0, respectively, and after approx. 60 minutes 2,512.0, 4,399.0 and 4,471.0 respectively.

During this time, the controls ran by approx. 30-40 counts per per minute, sometimes with a high initial background count of 100-200 counts per minute. per minute, which almost instantly died down to less than 100.

EXAMPLE 11 11 U3373

Water was added to clay until all the controls were cloudy and contained a bottom layer of water.

The medium containing 1 ml of the surfactant A received 0.5 ml of water. Easily became unclear and thus remained, although some isopropanol was added in an attempt to clear the system. The addition of isopropanol up to a total amount of 0.0? ml of isopropanol increased the turbidity of the system. At this point, the system was a stable, opaque macr oemulsion .λ. All other samples received only 0.10 ml of water, with the exception of the sample containing 3 ml of the surfactant A, which received 0.12 ml of water. All of these samples are clear both before and after counting.

After addition of water, the three samples of the medium containing the surfactant A had an initial count rate of 1 666.0, 4 190.0 and 10 320.0, respectively, while a count rate of 1 319.0, 3 353.0 and 7 134.0 after 36 minutes of counting time. The media containing the surfactant B had an initial count rate of 2 563.0, 3 730.0 and 6 364.0, respectively. After 36 minutes, the count rates were 2,034.0, 3,139.0 and 4,746.0. The surfactant C samples had initial count rates of 1 594.0, 2 814.0 and 9 063.0, respectively. , the count rates after 36 minutes were 1,180.0, 2,373.0, and 4,312.0, respectively.

EXAMPLE 12

Tritiated water (0.05 ml) was added to all the samples mentioned in Example 11. 91 000 counts per minutes were expected at 100 # efficiency after correction for natural decay of the material from January 10, 1964.

Ease stability and appearance of the samples remained exactly the same as noted in the previous example. However, a small amount of water appeared at the bottom of the ampoule used to count the medium containing 1 ml of the surfactant 0. Initial counts for the three samples containing 1, 2 and 3 ml of the micellar systems containing the surfactants A, B and 0 are 2937.0, 6755.0, 4309.0, 3627.0, 1667.0, 1367.0, 4190.0, 12 143373, 1441.0 and 1049.0, respectively. After oa. At 390 minutes, the final counts for these various samples were 2876.0, 6214.0, 3400.0, 3316.0, 1143.5, 606.5, 4020.5, 963.5 and 484.5, respectively. With regard to the systems containing the surfactants A, B and C, the following can be noted. Chemiluminescence was observed in all samples containing surfactants. This chemiluminescence decayed rapidly at first, but then persisted for a long time. The background counts in the systems prepared with these surfactants after approx. 156 minutes ranged from 800.0 to 5500.0 counts per minute. with small amounts of added water as described above after 390 minutes from 480 to 6000 counts per minute. minute.

The background count rate increased with the amount of surfactant added to the system. Where tritiated water was added to the systems, the counting efficiencies reached, at best, approx. 3%. In some cases, the counts per per minute of sample lower after the addition of the radioactive material than they were before any radioactive tritium was added. Apparently, the small amount of water added to the system can suppress the chemiluminescence process. Apparently, the tooth also suppresses the chemiluminescence process.

The two-phase control tests spoke with approximately the same efficiency as the best manufactured systems containing petroleum sulfonates.

EXAMPLE 13

A medium containing 2.0 ml by weight of 25.1% tall fatty acids, 24.2% n-hexanol, 15.8% isopropanol, 22.1% isooctylphenol polyethoxyethanol and 12.8% of a aqueous solution containing 25% NaOH and 15 ml of the toluene fluorescent mixture of Examples 1 and 10 and 0.4 ml of water. The initial count rates were 74.0, 55.0 and 54.0 counts per second. minute. 0.05 ml of tritiated water was added to the samples and counting rates of 34 207.0, 34 266.0 and 34 311.0 counts per unit were obtained. minute. These speeds represent counting by approx. 37 1 »efficiency. 1 ml of a solution containing equal parts of surfactant A and toluene fluorescent from Example 10 is added to the first of the three samples thus spoken. The color of the final mixture is approximately the same intensity of yellow as the original color of the surfactant solution. After 1 minute, the count was 13 U3373 speed. 39,973.0 and after 11 minutes it was 15,805.0. The decay of the velocity of speed with time is remarkable. Another subset of 1.0 ml of the surfactant A solution was added and counted. After 1 minute, the count rate was 54 729.0, but after 6 minutes it had dropped to 22,910.

In both cases, after adding the solution of the surfactant A in the stick, the counting rates were higher than that observed in the absence of the surfactant, but it died rapidly. If given sufficient time, the added petroleum sulfonate almost completely destroys the counting ability of media prepared from the micellar systems of the invention.

EXAMPLE 14

A system was prepared containing 2.0 g of an O 2 -C 2 g mixture (28 $, 28 $, 28 14%>) of n-alkanesulfonates, 1.0 ml of water and ca. 2.0 ml of isopropanol. 10 ml of the usual toluene fluorescent solution was added. The background radiation for these surfactant systems is 38.0 and 42.0. Then tritiated water (0.05 ml of the material used previously) was added. Counting rates of 6,010.0 and 6-066.0 were obtained.

In another sample prepared similarly, but with approx. 2.5 ml of isopropanol were obtained counts of 4,468.0, 4,402.0, 4,362.0 after adding 0.05 ml of tritiated water. This sample contained enough water to saturate the counting solution in the vial. Disee systems count by approx. 4.9-6.6 # efficiency.

The background count on the above test shows that the sulfonate group alone is not responsible for the apparent chemiluminescence in the medium. Somehow, however, it may contribute to the suppression which is evident at the low counting rates obtained. This is particularly clear, as several hours were spent preparing the above formulation, which spoke best of any of the spoken alkanesulfonate systems.

-type Example · 15

The procedure of Example .10 was followed except that 0.05 ml of tritiated toluene was added to each sample. The specific activity of c 14 143373

C

the tritiated toluene was 2.14 x 10 PM / ml on July 10, 1965. Oa.

98,000.0 counts per minutes at 100% efficiency should be expected after correction for decay of the material, as standardized d.

July 10, 1965. Only media containing 1 and 2 ml of the surfactants A, B and C are counted here and show respectively 10 586.0 '17 716.0 - 10 525.0 - 5 914.0 -6 916, 0 - 7,841.0. After approx. At 440 minutes, the count rates were 7,677.0 -14,241.0 7,042.0 and 2,177.0 - 3,882.5 - 2,005.5, respectively.

The control samples were initially between 53,000 and 60,000 and thus remain at the end of the counting period.

Claims (2)

Patent claims: A liquid scintillation count micellar medium comprising a small amount of dissolved scintillator effective to provide a countable scintillation in the medium by adding a radioactive sample thereto, and a scintillation solvent in an amount effective to allow reciprocal interaction between the dissolved scintillator and radiation from a radioactive sample added to the medium, characterized in that the medium contains several surfactants selected from (a) a combination of at least two surfactants, preferably an oil-soluble and a water-soluble; (b) a combination of anionic and nonionic surfactant; (c) a combination of cationic and nonionic surfactant; and (d) a combination of surfactant acting as a dispersant and surfactant acting as a surface tension reducing agent, which surfactants are present in an amount greater than that required to render the mixture thermodynamically stable and reducing. the vapor pressure of the liquid in the dispersed phase and that the surfactants, the dissolved scintillator and the scintillation solvent are substantially inert in chemical reactivity or energy transfer resulting in chemiluminescence, fluorescence or phosphorescence. The medium according to claim 1, characterized in that it contains a co-surfactant (cosurfactant).