JP5950411B2 - Method and apparatus for analyzing strontium 90 - Google Patents

Description

  The present invention relates to an analysis method and an analysis apparatus for strontium 90, which is the longest-lived radionuclide among strontium radionuclides. It relates to a method and a device that can be used.

  The radioactive material emits radiation such as α rays, β rays, and γ rays, and undergoes destruction to become more stable nuclei. At that time, the radionuclide emitting gamma rays can be identified by measuring with a germanium semiconductor detector having high energy resolution and excellent nuclide analysis. However, strontium 90 does not emit γ-rays, only β-rays are emitted, and strontium 90's daughter nuclide yttrium 90 is also β-disrupted, so that it cannot be identified and quantified by a germanium semiconductor detector. . In particular, β-rays emitted by strontium 90 and the like show a continuous spectrum. Therefore, in general, gas flow counters and liquid scintillation counters that measure β-rays overlap in a wide energy range and separate from other β-ray nuclides. Have difficulty. Therefore, it is common to chemically separate and purify only strontium and quantify strontium 90 with a gas flow counter. In the analysis of strontium 90, the energy of yttrium 90, the daughter nuclide, is greater in energy and easier to measure. The calculation method is generally performed.

  For example, when analyzing strontium 90 in seawater, 1) adsorb an appropriate amount of seawater through a large ion exchange resin column to adsorb strontium and the like, elute magnesium and calcium through the eluent through the same column adsorbing strontium, Hydrochloric acid is passed through the same column to elute strontium. (Preliminary concentration by a large ion exchange resin column); 2) Next, sodium hydroxide and sodium carbonate are added to the strontium-eluting hydrochloric acid to form a carbonate precipitate, and the precipitate is centrifuged. (Concentration of strontium by carbonate precipitation operation); 3) Next, the precipitate dissolved in hydrochloric acid is passed through an ion exchange resin to adsorb strontium and the like, and the eluent A is passed through the ion exchange resin to obtain calcium or the like. And eluent B is passed through the ion exchange resin to elute strontium (purification of strontium by ion exchange method); 4) the radioactivity of yttrium 90 produced from strontium 90 is measured. In order to improve the measurement accuracy, yttrium 90 is removed from the strontium eluate containing yttrium 90 together with the precipitate by scavenging operation, and yttrium 90 is newly generated from strontium 90 in the strontium eluate. Wait for it. (Removal of yttrium 90 by scavenging operation); 5) Finally, yttrium 90 newly generated from strontium 90 is collected together with the precipitate to obtain a radioactivity measurement sample, and the radioactivity is measured with an appropriate radioactivity measuring instrument. . (Preparation of Radioactivity Measurement Sample by Milking Operation and Radioactivity Measurement) Such a method for analyzing radioactive strontium is described in Non-Patent Document 1, for example.

Strontium 90 is a very troublesome radionuclide that accumulates in the bone when it enters the human body and keeps the hematopoietic organs for a long time, but cannot be measured with a handy dosimeter. Therefore, although it is measured by the method as described above, it takes a long time of 2 weeks (a period until the radiation equilibrium is reached) until new yttrium 90 is generated from strontium 90, and it is a complicated chemistry. Since it involves separation work, it cannot respond to a quick analysis request in an emergency. Furthermore, skilled skills are required for strontium concentration, purification, yttrium 90 removal operation, and the like.
Further, according to a generally known high frequency inductively coupled plasma mass spectrometer, although strontium 90 can be measured in a short time, it cannot be said that the measurement accuracy is sufficient.

Radioactive strontium analysis method Ministry of Education, Culture, Sports, Science and Technology, Science and Technology Policy Bureau, Nuclear Safety Division, Disaster Prevention and Environment Office, November 10, 2003 Published by Japan Analysis Center

  As described above, the conventional analysis method of strontium 90 requires a long time and complicated chemical separation work. Therefore, it cannot respond to a quick analysis request in an emergency and requires skilled skills. There's a problem. On the other hand, a known high frequency inductively coupled plasma mass spectrometer can measure strontium 90 in a short time, but it cannot be said that the measurement accuracy is sufficient.

  The present invention has been made in view of the above-described problems of the prior art, and provides a method and an apparatus capable of analyzing strontium 90 with high accuracy in a short time without the need for advanced measurement skills. The purpose is to do.

  In order to achieve the above object, the present inventor has a high-frequency inductively coupled plasma mass spectrometer (ICP-MS) possessed by many analysis institutions, which does not require special skills and can perform measurement in a short time. ) Was intensively studied on means for improving the measurement accuracy by ICP-MS. This ICP-MS is an elemental analysis device that realizes multi-element analysis in a short time, and includes a sample introduction unit, a plasma ion source, an interface cone (which may include a sampling cone, a skimmer cone, and a hyper skimmer cone), ion The lens, collision reaction cell, quadrupole mass filter and detector are the basic components.

<< High-frequency inductively coupled plasma mass spectrometer: ICP-MS >>
In general, a liquid sample is introduced into a nebulizer of a sample introduction portion and is aerosolized. The aerosol is introduced into the plasma ion source. In the plasma ion source, argon gas is introduced into the center of a high-frequency coil to which high-frequency energy is applied, and a strong high-frequency wave causes argon atoms to collide with each other to generate high-energy argon plasma. The aerosolized sample is instantly decomposed in plasma (temperature of 6000 to 10000 K), and the element to be measured is atomized and ionized. The ions are introduced into the ion lens portion through a pore of about 1 mm in a pair of orifices called a sampling cone and a skimmer cone (some devices have a hyper skimmer cone). The ion lens part serves to converge ions to separate ions and neutral substances and to block photons entering from the plasma. The collision / reaction cell introduces a non-reactive gas (He) into the cell, collides with interference ions, and uses the kinetic energy difference from the analysis target element to eliminate interference (collision mode) or reaction. A highly reactive gas (methane, ammonia, etc.) is introduced into the cell and reacted with interference ions to remove interference (reaction mode). A quadrupole mass filter consists of four parallel rod-shaped electrodes, and forms a quadrupole electric field by applying a voltage in which the DC electrodes and the high-frequency AC voltage are superimposed with the same polarity of the opposing electrodes. It is. When ions are introduced into a quadrupole electric field along a rod-shaped electrode with a low acceleration voltage, the ions move while oscillating vertically and horizontally, but if the voltage is changed while the ratio of DC voltage / AC voltage is kept constant. At a certain moment, only ions with a specific mass number oscillate stably and pass through the quadrupole, reaching a detector equipped with a secondary electron multiplier. On the other hand, ions having other mass numbers have a large amplitude, diverge, collide with the electrode, and disappear. The secondary electron multiplier is a detector that can detect a weak ion flow with high accuracy, and utilizes the property that secondary electrons are emitted when ions collide with the metal surface or specially processed ceramic surface. The emitted secondary electrons are accelerated by the electric field, and further amplified exponentially by repeating the collision. Eventually, secondary electrons are amplified from several hundred thousand times to ten million times or more, so that they can be taken out as a large signal current for each mass.

  ICP-MS is capable of 1) miniaturization, 2) high-speed scanning, 3) relatively inexpensive due to widespread use, 4) no need to obtain national qualifications for handling radiation, and 5) operation. Has many advantages such as easy. However, ICP-MS has a limit in mass resolution and can separate ions with different masses, but has the disadvantage that it cannot separate isobaric ions, and the analytical sensitivity of radioactive strontium. There is a disadvantage that it is not enough.

<< Important features of the present invention >>
Therefore, in order to eliminate the above-mentioned disadvantages, the present invention is characterized by “crude separation of isobaric matter by concentration of strontium” and “precise separation of isobaric matter by oxidation reaction”.
(1) Isobaric rough separation by concentration of strontium Nitric acid is added to a sample solution containing strontium (20-50% nitric acid solution), and the sample solution is a strontium molecular recognition resin (having the same ionic radius as strontium) For example, Eichrom Technologies' product name “Sr Resin” or 3M product name “Emporrad Disc Strontium” etc.) is introduced into the resin. Adsorb strontium. A washing liquid (20-50% nitric acid solution) is passed through the column on which strontium has been adsorbed to wash away substances other than strontium. Thereafter, the strontium adsorbed on the resin is eluted with an eluent (water or a 1% or less nitric acid solution), whereby a strontium-concentrated eluate can be obtained.
(2) Precise separation of isobaric bodies by oxygen reaction High purity oxygen is introduced into the collision reaction cell of ICP-MS, and the element that is highly reactive with oxygen is converted into another mass, thereby interfering with the interference. Can be removed. For example, if high-purity oxygen is introduced into ions containing ⁹⁰ Sr, ⁹⁰ Zr, and ⁹⁰ Y, ⁹⁰ Zr and ⁹⁰ Y are oxidized, and ⁹⁰ Zr ¹⁶ O (total mass number 106) and ⁹⁰ Y ¹⁶ O (total), respectively. By mass conversion to mass number 106), it can be discharged out of the system.

<< Strontium Analysis Method of the Present Invention >>
The method for analyzing strontium 90 according to the present invention having the above-mentioned important features includes introducing a sample solution into a strontium concentration separation column equipped with a strontium recognition resin that selectively recognizes strontium, and strontium recognition of the strontium concentration separation column. Adsorb strontium contained in the sample solution on the resin, elute the strontium adsorbed on the strontium recognition resin into the eluent, atomize the eluent containing strontium, introduce it into the plasma ion source, ionize it, The mass of ions other than ⁹⁰ Sr is converted in the quadrupole mass filter by introducing high-purity oxygen into the ion group mainly containing and oxidizing the element having high reactivity with oxygen to convert the ion mass of the element. Remove ions and pass through quadrupole mass filter The specific signal of ⁹⁰ Sr is measured. Such an analysis method can be automatically controlled by using appropriate software. In addition, the sample solution before being introduced into the strontium concentration separation column can be concentrated in advance to an appropriate concentration.

<< Strontium Analyzer of the Present Invention >>
The strontium 90 analyzer of the present invention includes a sample introduction unit having a nebulizer, a plasma ion source, an interface cone, an ion lens unit, a collision reaction cell, a quadrupole mass filter, a detector, In the high-frequency inductively coupled plasma mass spectrometer, the sample introduction unit has a strontium concentration separation column having a strontium recognition resin that selectively recognizes strontium, and the collision reaction cell has a high-purity oxygen supply means. It is characterized by having. Further, as an aid to increase the sensitivity, a high-sensitivity sample introduction device by desolvation such as an ultrasonic nebulizer can be used for the nebulizer. The high-sensitivity sample introduction device atomizes the sample solution with a coaxial nebulizer or ultrasonic transducer, and introduces elements in the sample solution into the plasma ion source with high efficiency by dehydration by passing through the heating and cooling units. To do.

The strontium 90 analyzer of the present invention is a strontium concentration separation column equipped with a strontium recognition resin that selectively recognizes strontium in front of a nebulizer of a sample introduction unit by applying a known high frequency inductively coupled plasma mass spectrometer. It is only necessary to add high-purity oxygen supply means to the collision / reaction cell, and it does not require advanced measurement skills, and automatic analysis of strontium 90 can be performed in a short time (15 to 20 minutes). it can. Moreover, the strontium 90 can be analyzed with high accuracy by including a strontium concentration separation column and a collision reaction cell capable of an oxidation reaction. According to the strontium 90 analysis method of the present invention using the strontium 90 analyzer, the strontium 90 can be quickly analyzed in an emergency without contact of the measurer with the sample to be measured and without individual differences between the measurers. Is possible.
According to the present invention, by using a high-sensitivity sample introduction device such as strontium concentration separation column and ultrasonic nebulizer, the analytical sensitivity of strontium 90 can be improved, and other than strontium concentration by the strontium concentration separation column. The separation accuracy of strontium 90 can be improved by separation of substances, precise separation of isobaric bodies by a collision reaction cell, and separation of ions other than a specific mass number by a quadrupole mass filter.

FIG. 1 is a diagram showing a schematic configuration of an apparatus suitable for carrying out the method for analyzing strontium 90 of the present invention. FIG. 2 is a diagram for explaining a method of adsorbing strontium on a strontium recognition resin that selectively recognizes strontium contained in a sample solution in a strontium concentration separation column. FIG. 3 is a diagram for explaining a method of eluting strontium adsorbed on a strontium recognition resin in a strontium concentration separation column and introducing it into a high frequency inductively coupled plasma mass spectrometer. FIG. 4 is a diagram showing an example in which concentration separation of a mixed standard solution containing 65 elements is performed using a strontium concentration separation column. FIG. 5 is a diagram for explaining the concept of isobaric interference removal by the collision reaction cell. FIG. 6 is a diagram showing changes in Sr, Zr, and Y ion counts (counts per second: cps) due to an oxidation reaction in the collision reaction cell. FIG. 7 is a diagram showing calibration curves of stable isotopes strontium and radioactive strontium.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. It goes without saying that the present invention is not limited to the following embodiments, and various variations and modifications are possible.

<< Strontium 90 analyzer >>
FIG. 1 is a diagram showing a schematic configuration of an apparatus suitable for carrying out the method for analyzing strontium 90 of the present invention. In FIG. 1, 1 is an autosampler (automatic preparatory device) storing a sample container filled with a sample solution obtained by eluting a sample to be analyzed into an appropriate lysis solution, and 2 is a strontium concentration separation column or filter 3, a nebulizer (coaxial nebulizer or ultrasonic nebulizer) 4, a plasma ion source 5, an interface cone 6, an ion lens 7, a collision / reaction cell 8 having a high-purity oxygen supply means 8 a, 1 shows a high-frequency inductively coupled plasma mass spectrometer equipped with a quadrupole mass filter 9 and a detector 10.

<Strontium concentration separation column>
In FIG. 1, a sample solution filled in a sample container stored in an autosampler (automatic sorting device) 1 is supplied to a strontium concentration separation column 2. FIG. 2 is a diagram for explaining a method of adsorbing strontium 90 to a strontium recognition resin that selectively recognizes strontium contained in a sample solution in a strontium concentration separation column.

《Strontium 90 adsorption process》
In FIG. 2, a sample solution containing strontium filled in a specific sample container set on an autosampler (automatic sorting device) 11 is sucked up and supplied by a pump 12. This sample solution is fed to the mixer 13 by the pump 12. On the other hand, the pump 14 has two flow paths and is supplied with a cleaning liquid (20 to 50% by volume nitric acid) or an eluent (ultra pure water). In the step of adsorbing strontium to the strontium recognition resin, the cleaning liquid is supplied to the pump 14 from the flow path on the cleaning liquid side. This cleaning liquid is fed to the mixer 13 by the pump 14. In the mixer 13, a sample solution containing strontium and a cleaning solution are mixed, and this mixed solution is applied to a strontium concentration separation column 15 or a filter provided with a strontium recognition resin that selectively recognizes strontium from the V4 valve through the port 4. Be sent. In the strontium concentration separation column 15, the liquid after adsorbing strontium on the strontium recognition resin is discarded from the port 2 through the valve V <b> 2 and the mixer 13. After feeding a certain amount of sample solution to the strontium concentration separation column 15, the probe of the autosampler 11 moves to the washing position containing the washing solution, and the washing solution is fed by the pump 12, and the inside of the strontium concentration separation column 15 is moved. Wash.

《Strontium elution process》
FIG. 3 is a diagram for explaining a method of eluting strontium adsorbed on a strontium recognition resin in a strontium concentration separation column and introducing it into a high frequency inductively coupled plasma mass spectrometer. In FIG. 3, in the step of eluting strontium adsorbed on the strontium recognition resin, the eluent is supplied from the pump 14. This eluent is fed from the V1 valve through the port 2 to the strontium concentration separation column 15 by the pump 14. In the strontium concentration / separation column 15, strontium adsorbed on the strontium recognition resin elutes into the eluent and is introduced from the port 4 to the high frequency inductively coupled plasma mass spectrometer (ICP-MS) via the V3 valve. A coaxial nebulizer, an ultrasonic nebulizer (USN), or the like is used as a nebulizer for introduction.
On the other hand, in preparation for the next analysis of strontium, in order to wash the pipe 16 from the pump 12 to the mixer 13, the adjustment liquid (20 to 50 vol% nitric acid) is sent to the mixer 13 through the pipe 16 by the pump 12. And discarded from the V4 valve via port 5.

<Concentrated separation of strontium>
FIG. 4 shows an example of carrying out concentration separation of a mixed standard solution containing 65 elements using the strontium concentration separation column configured as described above. The composition of this mixed standard solution is a 10 ml solution of 20% by volume nitric acid containing 2.5 μg of metal ions. The strontium recognition resin weighs 50 mg. In FIG. 4, the horizontal axis represents the element, and the vertical axis represents the adsorption rate (%) of the element adsorbed on the strontium recognition resin. As shown in FIG. 4, by using a strontium recognition resin, it is possible to almost completely remove zirconium, yttrium or the like having an ionic radius different from that of strontium. That is, 98% of the strontium contained in the mixed standard solution was captured, 99.77% of zirconium was removed, and 99.9% of yttrium was removed. In the strontium recognition resin, 98% of barium was captured, 85% of lead was captured, and tantalum and potassium were also captured. However, elements other than strontium, such as barium, lead, tantalum, and potassium, can be excluded by a quadrupole mass filter of a high-frequency inductively coupled plasma mass spectrometer. ^{Since 210} Pb, ²¹² Pb, and the like undergo β-decay in the same manner as ⁹⁰ Sr, ²¹⁰ Pb, ²¹² Pb, and the like may be erroneously recognized as ⁹⁰ Sr in the radiation analysis. However, by combining strontium concentration separation using a strontium recognition resin and a quadrupole mass filter, elements with a mass number different from strontium, such as ²¹⁰ Pb and ²¹² Pb, can be eliminated, and the analysis accuracy of strontium is improved. be able to.

《Removing isobaric interference with collision reaction cell》
As shown in FIG. 4, according to the concentration separation of strontium using a strontium recognition resin, 99.77% of zirconium and 99.9% of yttrium are removed. However, 0.23% of zirconium and 0.01% of yttrium are not removed and separated but remain contained in the solution. If a solution containing these small amounts of zirconium and yttrium is introduced into a high frequency inductively coupled plasma mass spectrometer, ⁹⁰ Sr, ⁹⁰ Zr and ⁹⁰ Y having the same mass number cannot be separated.
Therefore, in FIG. 1, by supplying the high purity oxygen in the collision reaction cell 8 from a high-purity oxygen supply means 8a, ⁹⁰ Zr and ⁹⁰ Y high reactivity with oxygen and oxidized, ^{respectively,} 90 ^{Zr 16} Mass converted to O and ⁹⁰ Y ¹⁶ O. These ⁹⁰ Zr ¹⁶ O and ⁹⁰ Y ¹⁶ O can be eliminated by a quadrupole mass filter. FIG. 5 is a diagram for explaining the concept of isobaric interference removal by the collision reaction cell.

  FIG. 6 is a graph showing changes in the ion counts of Sr, Zr, and Y due to the oxidation reaction in the collision reaction cell, the horizontal axis shows the oxygen flow rate (mL / min), and the vertical axis shows the ion count (count per second: cps). In the case of Sr, the ion count hardly changes even when the oxygen flow rate is changed. However, it can be seen that Zr and Y are clearly reduced by increasing the oxygen flow rate, and Zr and Y are effectively eliminated by the oxidation reaction in the collision reaction cell.

  As described above, the present invention can be applied to other than strontium by skillfully combining a strontium concentration separation column equipped with a strontium recognition resin, a collision reaction cell equipped with a high-purity oxygen supply means, and a quadrupole mass filter. Can be removed from the sample solution with a strontium concentration separation column, then the isobaric body can be removed with a collision reaction cell, and finally the non-target element can be completely removed with a quadrupole mass filter.

That is, for example, when ⁷⁴ Ge and ⁵⁴ Fe are included in the sample solution, ⁷⁴ Ge is converted into ⁷⁴ Ge ¹⁶ O ⁺ by an oxidation reaction in the collision reaction cell only in the collision reaction cell equipped with the high purity oxygen supply means. On the other hand, ⁵⁴ Fe reacts with the Ar plasma of the plasma ion source to become ⁵⁴ Fe ³⁶ Ar ⁺ , so these elements cannot be excluded. Even in the plasma ion source, ⁷⁴ Ge ¹⁶ O and ⁵⁴ Fe ³⁶ Ar are partially generated. However, since the present invention has a strontium concentration separation column equipped with a strontium recognition resin, ⁷⁴ Ge and ⁵⁴ Fe can be eliminated before being introduced into the plasma ion source by passing through this strontium concentration separation column. Yes (see FIG. 4).

<Calibration curve for stable isotopes strontium and radioactive strontium>
FIG. 7 is a diagram showing calibration curves of stable isotopes strontium and radioactive strontium, the horizontal axis indicates the concentration (ng / L), and the vertical axis indicates the ion count (count per second: cps). As shown in FIG. 7, it can be seen that radioactive strontium ⁹⁰ Sr has a measured intensity ratio approximately 1.25 times that of the stable isotope strontium ⁸⁸ Sr. Therefore, since the measurement intensity of radioactive strontium can be known from the measurement intensity of stable isotope strontium, even if there is no radioactive strontium standard solution or an analytical establishment that does not have a radiation control area, this calibration curve can be used to Analysis of ⁹⁰ Sr is possible, and environmental analysis can be carried out at many analysis institutions / analysis offices. On the other hand, if it is an organization that can handle radioactive strontium standard solution, the analytical accuracy can be further improved by creating a calibration curve with the radioactive strontium standard solution.

<Lower detection limit>
Table 1 below compares the detection lower limit value of the present invention with the detection lower limit value of another method.

  As shown in Table 1, it can be seen that the lower limit of detection of the strontium analysis method according to the present invention is sufficiently lower than other methods.

<< Comparison between the method of the present invention and the official method >>
Soil in a region with a high radiation dose rate within 20 km from TEPCO's Fukushima Daiichi Nuclear Power Station was collected, and the radiation dose measured by the method of the present invention and the official method (Milking method) were compared. Table 2 below shows an example.

As shown in Table 2, it was found that there was 95% reliability and no significant difference between the measured value of ⁹⁰ Sr by the method of the present invention and the official method.

  Since the method of the present invention can analyze strontium 90 with high accuracy in a short time and without requiring high measurement skills, it can be applied to various environmental analysis institutions and business establishments.

1 Autosampler (automatic sorting equipment)
2 Strontium enrichment separation column or filter 3 High frequency inductively coupled plasma mass spectrometer 4 Coaxial nebulizer or ultrasonic nebulizer 5 Plasma ion source 6 Interface cone 7 Ion lens 8a High purity oxygen supply means 8 Collision reaction cell 9 Quadrupole mass filter DESCRIPTION OF SYMBOLS 10 Detector 11 Sample solution filling container and autosampler 12 Pump 13 Mixer 14 Pump 15 Strontium concentration separation column or filter 16 Piping

Claims (1)

A sample solution is introduced into a strontium concentration separation column equipped with a strontium recognition resin that selectively recognizes strontium, and strontium contained in the sample solution is adsorbed on the strontium recognition resin of the strontium concentration separation column, and adsorbed on the strontium recognition resin. The strontium was dissolved in the eluent, the eluent containing strontium was atomized and introduced into the plasma ion source for ionization, and high purity oxygen was introduced into the group of ions mainly containing strontium ions to react with oxygen. Converting the mass of ions of the element by oxidizing a high element, then removing ions having a mass number other than ⁹⁰ Sr in the quadrupole mass filter, and identifying ⁹⁰ Sr that has passed through the quadrupole mass filter signal, trial in the strontium concentration and separation column The analysis method of 90Sr, characterized by measuring at from 15 since the solution was introduced 20 minutes.