Rapid determination of radiostrontium in seawater samples
- 598 Downloads
- 19 Citations
Abstract
A new method for the determination of radiostrontium in seawater samples has been developed at the Savannah River National Laboratory (SRNL) that allows rapid pre-concentration and separation of strontium and yttrium isotopes in seawater samples for measurement. The new SRNL method employs a novel and effective pre-concentration step that utilizes a blend of calcium phosphate with iron hydroxide to collect both strontium and yttrium rapidly from the seawater matrix with enhanced chemical yields. The pre-concentration steps, in combination with rapid Sr Resin and DGA Resin cartridge separation options using vacuum box technology, allow seawater samples up to 10 L to be analyzed. The total 89Sr + 90Sr activity may be determined by gas flow proportional counting and recounted after ingrowth of 90Y to differentiate 89Sr from 90Sr. Gas flow proportional counting provides a lower method detection limit than liquid scintillation or Cerenkov counting and allows simultaneous counting of samples. Simultaneous counting allows for longer count times and lower method detection limits without handling very large aliquots of seawater. Seawater samples up to 6 L may be analyzed using Sr Resin for 89Sr and 90Sr with a minimum detectable activity (MDA) of 1–10 mBq/L, depending on count times. Seawater samples up to 10 L may be analyzed for 90Sr using a DGA Resin method via collection and purification of 90Y only. If 89Sr and other fission products are present, then 91Y (beta energy 1.55 MeV, 58.5 day half-life) is also likely to be present. 91Y interferes with attempts to collect 90Y directly from the seawater sample without initial purification of Sr isotopes first and 90Y ingrowth. The DGA Resin option can be used to determine 90Sr, and if 91Y is also present, an ingrowth option with using DGA Resin again to collect 90Y can be performed. An MDA for 90Sr of <1 mBq/L for an 8 h count may be obtained using 10 L seawater sample aliquots.
Keywords
Strontium 90Sr 89Sr 90Y Seawater Rapid FukushimaIntroduction
There is an increasing need to develop faster analytical methods for emergency response, including emergency environmental samples [1, 2]. In light of the nuclear accident at Fukushima Nuclear Power Plant in March, 2011, there is a need for a rapid method for seawater samples which can be applied quickly with high chemical yields and effective removal of interferences. There are a number of analytical methods reported that use ion exchange/extraction chromatography to determine radiostrontium in seawater. Vajda and Kim provide a very thorough overview of recent radiostrontium separation and analytical measurement techniques for a wide range of sample matrices. Only a limited number of seawater methods, however, seem to be available. Many methods seem to use older, more tedious sample preparation steps or need improvements in chemical yield. Older methods which use very large cation exchange columns and multiple precipitations, for example, have a very low sample throughput [3].
This review also included more classical methods for water samples using fuming nitric precipitation as reported by Bojanowski and Knapinska-Skiba [4]. Fuming nitric acid presents safety and handling difficulties and can be very tedious and time-consuming. An additional precipitation step to remove barium as barium chromate is also required and chemical yields for Sr can be ~50–60 %.
Butkalyuk [5] reported an approach in which 90Y was collected from 1 L seawater samples using rare earth fluoride columns, with lead sulfide column being used to remove 210Bi, followed by Cerenkov counting. The method seemed to be limited to a 1 L sample aliquot and the presence of 91Y using this approach would interfere with 90Y measurements.
Grahek and Macefat [6] reported a newer method using Sr Resin (Eichrom Technologies, Inc. Lisle, IL). For 1 L seawater samples, an average Sr chemical yield of ~60 % was obtained, using a carbonate precipitation and Sr Resin separation. Cerenkov counting was used to avoid problems the method had from residual calcium. The counting efficiency, however, for Cerenkov counting of 89Sr is only about 38 %, adversely affecting the minimum detectable activity (MDA). An anion exchange method using alcohol was utilized to separate 90Y with a ~70 % chemical yield.
Based on this survey of the literature, a more rapid method to determine radiostrontium in seawater samples is needed. The method would need simple, effective pre-concentration steps and good chemical yields. By also utilizing simultaneous gas flow proportional counters (instead of sequential counters) and extended count times, smaller seawater aliquots (≪50 L) can be used with much easier handling and faster sample preparation throughput for analyses. This is particularly important in a radiological emergency, but also important to reduce labor costs and analysis times for routine operations.
The recent nuclear accident at Fukushima Nuclear Power Plant in March, 2011 highlights the need to have rapid analyses for radionuclides in environmental samples in the event of a nuclear accident, or even from a terrorist such as a radiological dispersive device (RDD) or improvised nuclear device (IND).
Rapid radiostrontium methods for water and air filter samples have been reported by the SRNL Laboratory in the past, applicable for emergency response samples containing high levels of beta interferences, as demonstrated by good performance on National Institute of Standards and Technology (NIST) NRIP samples containing high levels of gamma isotopes to simulate emergency response samples [7, 8]. These rapid methods employ calcium phosphate precipitation for water samples and accelerated digestion for air filter samples. Sr Resin cartridges with vacuum-assisted flow rates are used for rapid separations. Radiostrontium results were reported on water and air filter samples within ~3 h. When very high levels of interferences are present (where decontamination >1,000 is needed), a second Sr Resin purification step can be applied by adjusting the purified Sr eluent solution from the first column to ~5–6 M HNO3 and passing the solution through a second Sr Resin cartridge, followed by 8 M HNO3 rinsing, and final Sr elution using 0.05 M HNO3.
This two column approach using Sr Resin cartridges was applied to air samples received from the U. S. Embassy and other sites in Japan following the Fukushima Daiichi event in March, 2011. Gross alpha beta measurements on the filters showed the presence of high levels of beta activity for some air filter samples. It is also important to use 8 M HNO3 rinsing with Sr Resin to effectively remove 140Ba, since the k′ of Ba is reduced to <8 free column volumes in 8 M HNO3. Calcium phosphate precipitation, unlike time-consuming water evaporation methods, also reduces the levels of some potential sample interferences such as 137Cs, 134Cs and 131I [9]. It is important to note that Pb isotopes, which may be present in environmental samples, are retained on Sr Resin and remain on the resin when 0.05 M HNO3 is used to elute Sr [10].
When relatively high levels of Pb are present (higher uranium samples), it is possible for short-lived Bi isotopes to grow-in during the short elution step for Sr while Pb isotopes are retained on the resin. In that case, waiting 2–6 h after elution to allow unsupported Bi isotopes to decay may be warranted.
A new method for the determination of radiostrontium in seawater samples has been developed at the Savannah River National Laboratory (SRNL, Aiken, SC, USA) that allows rapid pre-concentration and separation of strontium and yttrium in seawater samples for the measurement of strontium and yttrium isotopes by gas flow proportional counting. While the method can be adapted for use with liquid scintillation or Cerenkov counting, gas flow proportional counting was selected to enable lower MDA and simultaneous counting of samples.
While radiostrontium in fresh water samples can be separated quickly and easily using calcium phosphate precipitation and a single 2 mL Sr Resin cartridge (Eichrom Technologies, Lisle, IL, USA), seawater samples can be much more difficult. The seawater matrix offers significant sample matrix challenges due to the high salt content, in particular, the stable strontium (~8 mg L−1), calcium (~400 mg L−1) and magnesium (~1,300 mg L−1) ion content. The stable strontium, in particular, limits the size of the seawater aliquot, depending on the amount of Sr Resin used.
The new SRNL method employs a rapid pre-concentration step that utilizes a calcium phosphate precipitation (enhanced with iron hydroxide) to collect both strontium and yttrium from the seawater matrix. The iron hydroxide appears to enhance the precipitation of strontium in particular, possibly due to the difficulties associated with achieving excess phosphate ions given the large amounts of calcium and magnesium ions present. The pre-concentration steps, in combination with a rapid Sr Resin separation using vacuum box technology, allow seawater samples up to 10 L to be analyzed for 89,90Sr using gas flow proportional counters. The pre-concentration steps can be performed quickly using 500 mL centrifuges tubes with no waiting on settling. Since iron has no adverse impact on Sr Resin or DGA Resin in nitric acid, this enhanced precipitation approach works very well. By using simultaneous gas flow proportional counting and long count times, low detection limits can still be achieved with sample aliquot volumes ≪50 L.
Several method approaches were investigated. The total 89Sr + 90Sr activity may be determined by gas flow proportional counting and recounted after ingrowth of 90Y to differentiate 89Sr from 90Sr. Soon after a nuclear accident, the total 89Sr + 90Sr detected from a release will be primarily 89Sr. It should be noted that a radiological event, such as a RDD containing 90Sr nuclear waste, for example, would be a predominantly 90Sr. In either case, once the source is identified through early measurements, the total 89Sr + 90Sr assay, which can be performed very quickly, has rapid screening value.
A second option was investigated. 90Y can be collected immediately using Sr Resin +DGA Resin (stacked) and counted to determine if the Sr isotope activity results from 90Sr (90Y) by comparison with the 89Sr + 90Sr results, however, 91Y is a problem for this approach. If 89Sr and other fission products are present, then 91Y (beta energy 1.55 MeV, 58.5 day half-life) will also typically be present. 91Y interferes with the collection of 90Y directly from the seawater sample without initial purification of Sr isotopes. Therefore, this stacked approach can simply be used as a confirmatory method, and the presence of 91Y is a problem. Since 91Y interferes, this is not recommended.
A better option seems to rapidly determine the total 89Sr + 90Sr, wait 1–10 days for 90Y ingrowth, and collect and purify 90Y using DGA Resin or Sr Resin to determine 90Y, and thus 89Sr and 90Sr, respectively. Sr Resin has been used to collect and separate 90Y from the Sr isotopes after ingrowth, but in that approach it is very important that no 89Sr or 90Sr bleeds through the Sr Resin and is collected with the 90Y. Under circumstances where 89Sr is very high and 90Sr is very low, the slightest bleed through of 89Sr through Sr Resin can change the 90Sr results significantly. This risk can be eliminated by using DGA Resin to purify 90Y. In addition, the DGA Resin separation offers additional removal of high levels of beta emitters that could affect relatively low levels of 90Y using this approach. While Y chemical yield may need to be determined, this may outweigh the risk of any 89Sr or 90Sr bleeding through the Sr Resin into the 90Y fraction.
The assay of 90Sr in seawater is of interest for oceanographic reasons due to its’ relatively long half-life (28.8 years). A 90Sr only method option was also developed using DGA Resin alone. DGA Resin has a very high retention of yttrium, and it can be easily purified using this resin. In addition, since strontium is not retained under strong nitric acid conditions, the amount of stable Sr in seawater is not a limiting factor.
Seawater samples up to 10 L may be analyzed for 90Sr using a DGA Resin method via collection and purification of 90Y only. If 89Sr and other fission products are present, then 91Y (beta energy 1.55 MeV, 58.5 day half-life) is also likely to be present. 91Y interferes with attempts to collect 90Y directly from the seawater sample without initial purification of Sr isotopes first and 90Y ingrowth. The DGA Resin option can be used to determine 90Sr with excellent removal of interferences, but if 91Y is present, an ingrowth option using DGA Resin again to collect 90Y can be performed.
The sample preparation steps to obtain purified 89Sr + 90Sr and/or 90Y (present initially in the sample) take <8 h to complete, and sample aliquots count times and may be adjusted based on MDA requirements. While two count methods after 90Y ingrowth can be applied, this counting method can lead to large uncertainties for the smaller radiostrontium isotope when ratios of 89Sr/90Sr are very large or very small. While the two count method can provide valuable information, there are times where purification of 90Y after ingrowth to differentiate 89Sr from 90Sr offers significant advantages.
Experimental
Reagents
Sr Resin (4, 4′, (5′) di-t-butylcyclohexane-18-crown-6) and DGA Resin (N,N,N′,N′ tetraoctyldiglycolamide) cartridges were obtained from Eichrom Technologies, Inc., (Lyle, Illinois, USA). Nitric, hydrochloric and hydrofluoric acids were prepared from reagent-grade acids (Fisher Scientific, Inc., Pittsburgh, PA, USA). All water was obtained from a Milli-Q2™ water purification system. All other materials were ACS reagent grade and were used as received. Radiochemical isotopes 90Sr were obtained from Eckert & Ziegler Analytics, Inc. (Atlanta, GA, USA) and diluted to the appropriate level.
Procedures
Column preparation
Sr Resin and DGA Resin was obtained as cartridges containing 2 mL of each resin from Eichrom Technologies, Inc. Sr Resin columns were stacked to achieve the desired resin volume (4 mL Sr Resin or 6 mL Sr Resin). Small particle size (50–100 μm) resin was employed, along with a vacuum extraction system (Eichrom Technologies).
Sample preparation
Operating Conditions for Perkin-Elmer DRC-e
| Plasma conditions | |
| RF power (W) | 1,400 |
| Torch depth (mm) | 5.5 |
| Plasma gas (L/min) | 15 |
| Carrier gas (L/min) | 1 |
| Nebulizer gas (L/min) | 0.98 |
| Sample pump (rps) | 5 |
| Ion lens/quadrupole | |
| E1 lens voltage (V) | 6.25 |
| E1 lens slope | 0.0165 |
| E1 lens intercept | 4.413 |
| Cell path voltage (CPV) | −12 |
| Cell rod offset (V) | −17 |
| Q-pole rod offset (V) | −4 |
| Detector | |
| Discriminator (V) | 17 |
| Analog HV (V) | −1,550 |
| Pulse HV (V) | 900 |
| Typical tune | |
| Counts | >300,000 cps In-115 at 10 μg/L |
| RSD% | <5 % |
| Oxide 156/140 | <5 % |
| Background | <10 cps at mass 220; <10 cps at mass 8.5 (vacant mass for noise detection only) |
| Resolution | 0.60–0.80 amu at 10 % peak height |
| Data acquisition | |
| Integration | 1,000 ms dwell time 50 ms |
| Replicates | 3 with 20 sweeps/reading |
Rapid sample preparation method for 89Sr + 90Sr in seawater
For a 2 L seawater aliquot, 200 mg of Fe3+ as iron nitrate, 1 mg stable yttrium (if 90Y was determined immediately using DGA Resin) and 25 mL 3.2 M ammonium hydrogen phosphate were added. The pH was adjusted to ~10 by adding 30 mL 14.5 M ammonium hydroxide and stirring to mix well.
The samples were centrifuged using 500 mL centrifuge tubes, splitting the samples between two 500 mL tubes and centrifuging for ~6 min @3,400 rpm. The supernatant was discarded. The rest of the 2 L seawater aliquot was centrifuged using the same two 500 mL tubes. The calcium phosphate/iron hydroxide mixed precipitate was redissolved in a total of 25 mL 15.8 M HNO3 (15 mL, then 10 mL volumes), transferring dissolved solids from one of the replicate tubes to the next tube and then into a 600 mL glass beaker. The tubes were rinsed with a total of 8 mL 2 M aluminum nitrate and ~5 mL 3 M HNO3, which was used to rinse the replicate centrifuge tubes and then transferred into the 600 mL glass beaker. Each dissolved sample precipitate was evaporated to a volume of ~25 mL on a hot plate and transferred to a 50 mL centrifuge tube. The glass beaker was rinsed with two 5 mL volumes of 1 M HNO3, which were added to the 50 mL tube. Each sample tube was warmed slightly in a hot block and centrifuged ~5 min to remove any residual solids. If any residual solids remained, these were rinsed with ~3–5 mL 8 M HNO3, centrifuged to remove the solids and this rinse was added to the load solution.
It should be noted that smaller volume seawater aliquots (200, 500 mL, etc.) can be processed in the same way even more quickly, if a higher MDA is still sufficient to meet measurement quality objectives.
Column separation
Rapid separation method for 89Sr + 90Sr in seawater (90Y in growth option)
This solution was transferred to preweighed planchets and evaporated on a hot plate with medium heat to dryness. Two milliliters 0.05 M HNO3 were used to rinse each tube and then was transferred to each planchet, and evaporated to dryness on a hot plate. The dried planchets were allowed to cool and then were weighed to determine gravimetric carrier recovery. The planchets were counted by simultaneous gas flow proportional counting (Tennelec LB 4100) for 120 min. Longer count times to significantly lower MDA can be performed. The detectors were calibrated using NIST Traceable 90Sr/90Y sources matching the sample geometry. Detector backgrounds are determined and subtracted from the sample counts. A mass attenuation correction factor was determined experimentally using prepared mounts containing 90Sr/90Y (>167 Bq) and a nominal amount of Sr carrier.
Rapid separation method for 90Sr in seawater (DGA Resin only)
Apparatus
Polycarbonate vacuum boxes with 24 positions and a rack to hold 50 mL plastic tubes were used. Two boxes were connected to a single vacuum source by using a T-connector and individual valves on the tubing to each box.
Planchets were annealed for ~4 h in a furnace at 550 °C prior to use. This provides chemical resistance to the planchets so that iron oxide does not form during evaporation of the nitric acid, which would cause error in the gravimetric weights.
Results and discussion
Table 1 shows the measured values for 90Sr in a set of eleven 1 L seawater samples spiked at the 148 mBq/L level. The average 90Sr result was 149.8 ± 11 mBq/L (1SD, standard deviation) with an average bias of 1.2 %. The average stable Sr carrier recovery was 88.8 % (1 SD = 5.3 %), indicating very good chemical yield. The stable Sr level in the seawater used was determined by ICP-MS to be 7.66 mg Sr L−1. The uncertainty in this ICP-MS assay is ~1.5 % at 1 SD.
90Sr in seawater results using Sr Resin (1 L samples)
| Sample ID | Sr carrier (%) | 90Sr reference value (pCi/L) | 90Sr reference value (mBq/L) | 90Sr measured value (mBq/L) | Difference (%) |
|---|---|---|---|---|---|
| 1 | 94.1 | 4.0 | 148.0 | 150.6 | 1.8 |
| 2 | 91.4 | 4.0 | 148.0 | 138.5 | −6.4 |
| 3 | 86.5 | 4.0 | 148.0 | 146.4 | −1.1 |
| 4 | 96.2 | 4.0 | 148.0 | 127.0 | −14.2 |
| 5 | 83.3 | 4.0 | 148.0 | 146.4 | −1.1 |
| 6 | 86.2 | 4.0 | 148.0 | 153.7 | 3.9 |
| 7 | 82.9 | 4.0 | 148.0 | 161.1 | 8.9 |
| 8 | 90.5 | 4.0 | 148.0 | 159.9 | 8.0 |
| 9 | 89.4 | 4.0 | 148.0 | 134.2 | −9.3 |
| 10 | 87.3 | 4.0 | 148.0 | 170.5 | 15.2 |
| 11 | 88.9 | 4.0 | 148.0 | 159.8 | 8.0 |
| Avg | 88.8 | 149.8 | 1.2 | ||
| SD | 5.3 | 11.0 | |||
| % RSD | 5.9 | 7.3 | |||
| Seawater assay by ICP-MS (mg Sr/L) | 7.66 | ||||
| 1 L sample aliquot | |||||
| 2 h count time | |||||
90Sr in seawater results using DGA Resin (90Y-1 L samples)
| Sample ID | Y carrier (%) | 90Sr reference value (pCi/L) | 90Sr reference value (mBq/L) | 90Sr measured value (mBq/L) | Difference (%) |
|---|---|---|---|---|---|
| 1 | 93.8 | 4.0 | 148 | 160.0 | 8.1 |
| 2 | 95.9 | 4.0 | 148 | 166.4 | 12.4 |
| 3 | 94.0 | 4.0 | 148 | 153.9 | 4.0 |
| 4 | 96.5 | 4.0 | 148 | 155.1 | 4.8 |
| 5 | 92.1 | 4.0 | 148 | 149.4 | 0.9 |
| 6 | 96.0 | 4.0 | 148 | 157.7 | 6.6 |
| 7 | 96.0 | 4.0 | 148 | 142.5 | −3.7 |
| 8 | 95.2 | 4.0 | 148 | 150.0 | 1.4 |
| 9 | 95.0 | 4.0 | 148 | 153.2 | 3.5 |
| 10 | 96.3 | 4.0 | 148 | 139.5 | −5.7 |
| 11 | 94.1 | 4.0 | 148 | 151.1 | 2.1 |
| Avg | 95.0 | 152.6 | 3.1 | ||
| SD | 1.6 | 7.6 | |||
| % RSD | 1.7 | 5.0 | |||
| Y carrier by ICP-MS | |||||
| 1 L sample aliqout | |||||
| 2 h count time | |||||
The average stable Sr carrier recovery was 81.9 % (1 SD = 4.1 %), indicating very good chemical yield, despite increasing the sample aliquot to 2 L.
90Sr in seawater results using Sr Resin (2 L samples)
| Sample ID | Sr carrier (%) | 90Sr reference value (pCi/L) | 90Sr reference value (mBq/L) | 90Sr measured value (mBq/L) | Difference (%) |
|---|---|---|---|---|---|
| 1 | 80.6 | 4.0 | 148 | 154.8 | 4.6 |
| 2 | 84.9 | 4.0 | 148 | 151.1 | 2.1 |
| 3 | 85.5 | 4.0 | 148 | 150.0 | 1.4 |
| 4 | 76.7 | 4.0 | 148 | 160.7 | 8.6 |
| Avg | 81.9 | 154.2 | 4.16 | ||
| SD | 4.1 | 4.8 | |||
| % RSD | 5.0 | 3.1 | |||
| Seawater assay by ICP-MS (mg Sr/L) | 7.70 | ||||
| 2 L sample aliquot | |||||
| 2 h count time | |||||
90Sr in seawater results using DGA Resin (90Y-2 L samples)
| Sample ID | Y carrier (%) | 90Sr reference value (pCi/L) | 90Sr reference value (mBq/L) | 90Sr measured value (mBq/L) | Difference (%) |
|---|---|---|---|---|---|
| 1 | 87.0 | 4.0 | 148 | 148.1 | 0.1 |
| 2 | 93.2 | 4.0 | 148 | 157.9 | 6.7 |
| 3 | 88.0 | 4.0 | 148 | 163.8 | 10.7 |
| 4 | 88.0 | 4.0 | 148 | 161.5 | 9.1 |
| Avg | 89.1 | 157.8 | 6.6 | ||
| SD | 2.8 | 6.9 | |||
| % RSD | 3.2 | 4.4 | |||
| Y carrier by ICP-MS | |||||
| 2 L sample aliquot | |||||
| 2 h count time |
90Sr in seawater results using DGA Resin only (90Y)
| Sample ID | Smp. vol. (L) | Y carrier (%) | 90Sr reference value (pCi/L) | 90Sr reference value (mBq/L) | 90Sr measured value (mBq/L) | Difference (%) |
|---|---|---|---|---|---|---|
| 1 | 4 | 91.6 | 20.0 | 740 | 725 | −2.0 |
| 2 | 4 | 88.7 | 2.0 | 74 | 74 | 0.0 |
| 3 | 10 | 94.3 | 2.0 | 74 | 74 | 0.0 |
| 4 | 10 | 94.5 | 2.0 | 74 | 66 | −10.8 |
| 5 | 10 | 90.2 | 2.0 | 74 | 76 | 2.7 |
| Avg | 91.9 | −2.0 | ||||
| SD | 2.5 | |||||
| % RSD | 2.8 | |||||
| Y carrier by ICP-MS | ||||||
| 2 h count time | ||||||
The tests indicate that radiostrontium can be measured very well using Sr Resin, and that 90Sr can be analyzed using DGA Resin only (a single 2 mL cartridge per 2 L sample replicate). The sample pre-concentration steps to remove the seawater matrix worked very well. Chemical yields were very good and no column flow issues were observed. The use of iron hydroxide along with calcium phosphate to enhance the precipitation was effective, and tests demonstrate that up to 10 L of seawater can be analyzed by combining purified replicates, working with 2 L aliquots. When calcium phosphate alone was tested Sr yields were only 60–70 %.
Due to the Sr capacity limitations of Sr Resin and the large amounts of stable Sr in seawater, the 2 L samples required 6 mL of Sr Resin to separate 89Sr and 90Sr. Three 2 L aliquots of seawater can be processed using 6 mL of Sr Resin be combining purified replicates. Larger aliquots would require and inordinate amount of Sr Resin to perform the separation.
In low-level counting, where a zero background count is quite common, the constant 3 is used to prevent an excessively high false positive rate.
The MDA for the results can be adjusted as needed, depending on the sample aliquot and count time. For a 2 L sample aliquot, the method MDA for 89Sr and/or 90Sr with a 120 min count time is 9.1 mBq/L. For a 6 L sample aliquot, the method MDA for 89Sr and/or 90Sr with a 1,000 min count time is 1 mBq/L. For a 10 L sample aliquot (DGA only option), the method MDA for 90Sr with a 1,000 min count time is 0.61 mBq/L.
The method can be applied to smaller seawater sample aliquots (even more rapidly) if slightly higher MDA levels are adequate for emergency response measurements, depending on the measurement quality objectives following an incident. The option to perform a second Sr Resin separation when a decontamination factor of greater than ~1,000 is needed to ensure sufficient removal of high levels of beta interferences is also a recommended.
The combination of Sr Resin to assay total 89Sr + 90Sr, followed by DGA Resin to collect and purify 90Y is a powerful combination and avoids any breakthrough of high levels of 89Sr into the 90Y fraction when high levels of 89Sr are present. The ingrowth time for 90Y may only need to be a 3–5 days, depending on levels present and MDA needs to facilitate more rapid results.
Conclusions
A new method to determine 89Sr and 90Sr has been developed that allows the rapid separation of radiostrontium in seawater samples with high chemical yields and effective removal of interferences. The simple matrix removal steps and rapid column separation steps resulted in reliable measurements of radiostrontium isotopes at very low levels from 1 to 10 L sample aliquots. Simultaneous gas flow proportional counters with longer count times can be used to reduce the amount of seawater samples processed.
Notes
Acknowledgments
This work was performed under the auspices of the Department of Energy, DOE Contract No. DE-AC09-96SR18500.
References
- 1.Larivière D, Cumming T, Kiser S, Li C, Cornett R (2008) Automated flow injection system using extraction chromatography for the determination of plutonium in urine by inductively coupled plasma mass spectrometry. J Anal At Spectrom 23:352CrossRefGoogle Scholar
- 2.Stricklin DL, Tjarnhage A, Nygren U (2002) Application of low energy gamma-spectrometry in rapid actinide analysis for emergency preparedness. J Radioanal Nucl Chem 251(1):69CrossRefGoogle Scholar
- 3.Vajda N, Kim CK (2010) Determination of radiostrontium isotopes: a review of analytical methodology. Appl Radiat Isot 67:2306CrossRefGoogle Scholar
- 4.Bojanowski R, Knapinska-Skiba D (1990) Determination of low-level 90Sr in environmental samples: a novel approach to the classical method. J Radioanal Nucl Chem 138(2):207CrossRefGoogle Scholar
- 5.Butkalyuk PS (2009) Rapid determination of 90Sr in seawater. Moscow Univ Chem Bull 64:165CrossRefGoogle Scholar
- 6.Grahek Z, Macefat M (2005) Determination of radioactive strontium in seawater. Anal Chim Acta 534:271CrossRefGoogle Scholar
- 7.Maxwell S, Culligan B (2009) Rapid separation method for emergency water and urine samples. J Radioanal Nucl Chem 279(3):901CrossRefGoogle Scholar
- 8.Maxwell S, Culligan B, Noyes G (2010) Rapid separation method for actinides in emergency air filter samples. Appl Radiat Isot 68(12):2125CrossRefGoogle Scholar
- 9.Rapid radiochemical methods in support of Fukushima presentation at radiobioassay and radiochemical measurements conference Eichrom user’s group meeting, 2nd November 2011. http://www.eichrom.com/radiochem/meetings/2011/rrmc/pdf/4-Maxwell-Eichromworkshop2011.pdf
- 10.Horwitz EP, Chiarizia R, Dietz M (1992) A novel strontium-selective extraction chromatographic Resin. Solvent Extr Ion Exch 10:313CrossRefGoogle Scholar
- 11.Maxwell SL, Culligan BK, Utsey RC, McAlister DR, Horwitz EP (2012) Rapid method for determination of 228Ra in water samples. J Radioanal Nucl Chem, Online firstGoogle Scholar
- 12.Currie LA (1968) Limits for qualitative and quantitative determination. Anal Chem 40:586CrossRefGoogle Scholar