Options for 89Sr and 90Sr
Determination$1--

6XPPDU\   There are many methods (Table 1) available for the measurement of radiostrontium (Table 2) fromenvironmental, building materials, or biological samples. Typically, analysts are interested in the measurement of thefission products 89Sr (decays to stable 89Y) and 90Sr (decays to E- emitting 90Y). Stable strontium or 85Sr may also beused as a chemical yield tracer. Methods typically begin with a concentration or matrix removal step, followed by theseparation of strontium from interfering nuclides using Sr Resin (Figure 1A). Methods may also incorporate steps todiscriminate between 89Sr and 90Sr, including multiple counts, nuclide selective counting techniques and ingrowth andsecondary separations of 90Y (daughter of 90Sr). Measurement instrumentation includes low background gas flow
proportional counting (GFPC), liquid scintillation (LSC), Cerenkov counting, and inductively coupled plasma-mass
spectrometry (ICP-MS).
This application note will offer guidance in choosing an appropriate method for the determination ofradiostrontium, taking into account process knowledge, available measurement equipment and data quality objectives(required detection limits, urgency of measurement, age of sample, and need for 89/90Sr discrimination). The
measurement methods are meant be to used in concert with the appropriate sample preparation method for the matrix
being analyzed. For a more comprehensive treatment of sample preparation methods, see the application notes
available at http://www.eichrom.com/eichrom/appnotes/applications/index.aspx. A detailed discussion of interferences
for the various measurement techniques can also be found in references [2] and [5].
Table 1. Summary of 89/90Sr Method Options
PrimarySeparation

MethodICP-MS
Total 89/90Sr

1A1A90

1CY Direct89

90

Two Count Sr and Sr
89908990

Rapid Sr and Sr
90

Cerenkov Sr and Sr( Y)
Gas Flow Porportional

Primary
Measurement

SecondarySeparation

SecondaryMeasurement

Sr Yield
Monitor

Ref.

Sr by ICP-MS
Sr by GFPC/LSC

None
None

None
None

Stable Sr
Stable Sr

14,5

Y by GFPC/LSC/Cerenkov

None

None

Stable Sr

6

Sr by GFPC/LSC*

Stable Sr

289/90Stable Sr

585349089/9090

1A89/90

1A89

1A
1A89

Sr by GFPC/LSC

Sr by Cerenkov
Sr by Cerenkov
Sr by GFPC

89/90

None
None
1B or 1C
1B or 1C

89/90

Sr by LSC

90

Y by Cerenkov
90
Y by GFPC

Stable Sr/ Sr
Stable Sr/85Sr*89Sr/90Sr descrimination by solving equations for 89Sr decay and 90Y ingrowth during time between 2 measurements

NuclideStabel Sr
85

Sr

89

Sr90

Sr90

Y

Half-Life
84

Decay
Mode

Table 2. Properties of Selected Nuclides
Detector Suitable for Measurement
EnergyGFPCLSC
Cerenkov MS/AES Gamma

868788Sr (0.56%), Sr(9.86%), Sr (7.0%), Sr (82.58%)

64.849 days
50.563dayse/g

28.79 years

b-64 hours

b-b-g = 514 keV (96%)
b max = 1500 keV
b mean = 587 keV
b max = 546 keVb mean = 196 keV
b max = 2280 keV
b mean = 934 keV

No

No

No

Yes

No

No

Yes

No

No

Yes

Yes

Yes

Yes

No

No

Yes

Yes

No

Yes

No

Yes

Yes

Yes

No

No)LJXUH6WURQWLXP6HSDUDWLRQ2SWLRQV
A. Sr separation (Sr Resin)
Sr Resin
2-4 mL in cartridges(1) Precondition Sr Resin with
3 bed volumes 8M HNO3.
(2) Load sample at 1-2 mL/min.
(3) Rinse sample tube with 5 mL
8M HNO3.
(4) Add tube rinse to Sr Resin.
Elute at 1-2 mL/min.

B. Sr/90Y Separation (Sr Resin)
Sr Resin
2 mL cartridge(1) Dissolve Sr Residue from planchet
used for total 89/90Sr measurementwith 5 mL 8M HNO3.
(Or acidify Cerenkov sample to8M HNO3.)(2) Using transfer pipet, transfer
dissolved residue to 15mL c- tube.

(3) Rinse planchet with 5 mL(5) Rinse Sr Resin sequentially with*
8M HNO3. Add to 15 mL c-tube.
- 3 bed volumes 8M HNO3.
(4) Precondition 2 mL Sr Resin- 3 bed volumes 3M HNO3 - 0.05M
cartridge with 5 mL 8M HNO3.
oxalic acid.
(5) Load sample at 1-2 mL/min,- 3 bed volumes 8M HNO3.
collecting eluate (90Y-fraction).

(6) Dispose of (1) to (5) as waste.
(7) Strip Sr with 5 bed volumes
0.05M HNO3 at 1 mL/min.
*Rinse solutions and volumes listed aregeneral guidelines. See detailed app. notesfor recommended rinsing for each matrix.

(6) Rinse c-tube with 5 mL 8M HNO3.
(7) Add tube rinse to column. Elute,collecting eluate (90Y fraction).
Method appropriate for high 90Sr/89Sr ratios or
90Sr confirmation. Potential for 1-3% Sr breakthrough, limits application for high 89Sr/90Srratios.

C. Sr/90Y Separation (DGA Resin)
DGA Resin, Normal
2 mL cartridge(1) Dissolve Sr Residue from planchet
used for total 89/90Sr measurementwith 5 mL 8M HNO3. (Or acidifyCerenkov sample to 8M HNO3.)(2) Transfer dissolved residue to15mL c-tube.
(3) Rinse planchet with 5 mL
8M HNO3. Add to 15 mL c-tube.
(4) Precondition 2 mL DGA Resincartridge with 5 mL 8M HNO3.
(5) Load sample at 1-2 mL/min.
(6) Rinse c-tube with 5 mL 8M HNO3.
(7) Add tube rinse to cartridge.
(8) Rinse DGA with 15 mL 0.1M HNO3.
(9) Save (4) to (8) as Sr fraction.
(10) Strip 90Y with 10 mL 0.1M HCl.
Preferred method for high 89Sr/90Sr ratios.
Additional rinses may be required for directdetermination of 90Sr via 90Y, see AN-1414.

,&3-06 6URQO\ 90Sr may be determined by inductively coupled plasma-mass spectrometry (ICP-MS)
following separation on Sr Resin (Figure 1A). However, due to the relatively short half-life of 90Sr, application to lowlevel environmental analyses will be limited by the available mass spectrometry technology and concentration
chemistries. Recent publications suggest detection limits of ~1Bq/g are possible. However the achievable detection limit
will depend on several factors, including sample type, sample size, and the age and type of MS instrument available [1].
Radiometric techniques will allow lower detection limits for 90Sr and the ability to also determine 89Sr.
Accurate measurement of strontium chemical yield as 88Sr by ICP-MS has very little chance for impact by
isobaric interferences (87Rb-H+, which should be effectively removed by Sr Resin Separation). 90Zr is the only
significant isobaric interference for 90Sr measurement. Separation chemistries should be tailored to ensure complete
removal of zirconium (rinsing with 3M HNO3-0.05M oxalic acid for Sr Resin separations). Determination of 90Sr by ICPMS greatly simplifies the calculation of 90Sr activity, which can be complicated in radiometric detection techniquesby the ingrowth of 90Y and the decay of 89Sr.
ICP-MS and ICP-AES (atomic emission spectrometry) are also very effective tools for the determination ofstrontium chemical yield when using radiometric detection methods for 89Sr and 90Sr. ICP-MS and ICP-AES will often
give more precise chemical yield data than gravimetric techniques, while also allowing the use of less Sr carrier (<1 mgvs 4-10 mg stable Sr). Many environmental samples (soils, brines, sea water and some ground waters) may containsignificant levels of stable strontium. Pre-anlysis of these samples by ICP-MS or ICP-AES for native Sr content may benecessary to adjust the amount of stable Sr yield monitor added and to ensure accurate measurement of the Sr yieldthroughout the separation process.

7RWDO 6U    In instances where 90Sr is the only radiostrontium isotope likely to be present or where total 89Sr +90Sr determination is desired, radiostrontium may be determined by liquid scintillation counting or gas flow proportionalcounting following separation on Sr Resin (Figure 1A). Confirmation of 90Sr activity will require discrimination from89Sr through two count methods and calculations [2], ingrowth and separation of 90Y (Figure 1B or 1C) [4,5] or selective
89Sr/90Y measurement(s) using Cerenkov counting [3].
6U E\ 'LUHFW 5HFRYHU\ RI <    In the analysis of debris from decommissioning of older facilities or otherinstances where 90Sr is likely to be present in the absence of short-lived fission products (91Y, 89Sr, etc.) andwhere 90Y is in equilibrium with 90Sr, 90Sr may be determined by liquid scintillation, gas flow proportional counting, orCerenkov counting following the direct separation of 90Y on DGA Resin (Figure 1C) [6]. The very high retention of90Y on DGA resin allows recovery of 90Y from difficult matrices, large sample volumes, and/or samples with highnative Sr content that may prove problematic using the isolation of Sr on Sr Resin. However, the presence of freshfission products, such as 91Y and rare earth radionuclides, will cause significant positive bias in the 90Sr
determination performed using this method. Stable yttrium carrier yield can be measured by ICP-MS or ICP-AES.
7ZR &RXQW 0HWKRG    Total 89/90Sr can be measured in an initial count using GFPC or LSC following separation
on Sr Resin (Figure 1A). Following a period of ingrowth for 90Y, the samples can be counted again, and individual 89Srand 90Sr activities calculated by solving a series of equations related to the decay of 89Sr and the ingrowth of 90Y (twocount method) [2]. Ideally, the initial count is performed as quickly as possible following the separation on Sr Resinto minimize 90Y ingrowth. The second count is ideally performed after 1-2 weeks of 90Y ingrowth. Computational
methods for resolving the 89Sr and 90Sr activities are outlined in Appendix B of reference [2].
&HUHQNRY YV /6&     The beta emission of 90Sr is below the threshold for efficient measurement by Cerenkov
counting (LSC without addition of cocktail). 89Sr may be determined by Cerenkov counting immediately following
separation of radiostrontium on Sr Resin (Figure 1A). 90Y will also be efficiently measured by Cerenkov counting.
Counting of 89Sr by Cerenkov counting is less efficient than by liquid scintillation (LSC). However, the lower
counting efficiency is partially offset by the lower background observed in Cerenkov counting. Furthermore, Cerenkov
counting eliminates interferences from many low energy beta emitters that may cause bias in measurements made by
LSC or GFPC. Additionally, Cerenkov counting does not require the addition of cocktail, offering cost savings in waste
disposal and reagent costs. Cerenkov counting does not suffer from quenching which can occur in liquid scintillation.
Counting 89Sr by Cerenkov or total 89/90Sr by GFPC as a first measurement leaves open the option to separate 90Y
from the strontium fraction for further confirmation of 90Sr or discrimination of 89Sr/90Sr. Counting the strontium fraction by
LSC limits any further separation on the sample due to the addition of the LSC cocktail, leaving the two count method as
the only viable 89Sr/90Sr discrimination option after LSC measurements of 89/90Sr, unless the sample is split prior to LSC.
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6U E\ &HUHQNRY 6U E\ /6& &RXQWLQJ 5DSLG 6U     89Sr is determined by Cerenkov counting
immediately following separation of radiostrontium on Sr Resin (Figure 1A) [3]. After the addition of LSC cocktail, 90Sr
may then be determined by measuring total radiostrontium (89Sr + 90Sr) by standard liquid scintillation counting andcalculating the difference (total radiostrontium - 89Sr), taking into account ingrowth of 90Y and decay of 89Sr duringcounting.
This approach may not be appropriate for samples that require long count times to meet data quality
objectives or for samples with low ratios of 89Sr/90Sr, due to interference from 90Y ingrowth. However, this method can beused very effectively to rapidly determine 89Sr and 90Sr in samples containing relatively high amounts of radiostrontium
in the immediate aftermath of a release of fresh fission products.
When utilizing Cerenkov and/or liquid scintillation counting, chemical yield of Sr throughout the separation
process is most effectively measured via stable strontium carrier by taking a small aliquot of the separated strontium
fraction for analysis by ICP-MS or ICP-AES. Recovery by 85Sr gamma emission is not recommended, due tointerference with the measurement of total radiostrontium by liquid scintillation counting.

'*$ YV 6U 5HVLQ IRU < 6HSDUDWLRQ    For samples with expected high ratios of 89Sr/90Sr, using DGA toselectively retain 90Y (Figure 1C) is recommended, as the Sr can be effectively rinsed from the column, while 90Y
recovery remains strongly adsorbed (k’ Y on DGA >>1000). In high 89Sr/90Sr samples, small breakthrough of strontium
from separation on Sr Resin (Figure 1B) into the 90Y fraction (k’ Sr only ~100 on Sr Resin) can lead to high bias of the90Sr measurement and a corresponding low bias of the 89Sr.
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6U E\ &HUHQNRY < E\ &HUHQNRY )ROORZLQJ ,QJURZWK DQG 6HSDUDWLRQ    89Sr is measured byCerenkov counting following separation of strontium on Sr Resin (Figure 1A). 90Sr may then be determined by waiting
1-14 days for 90Y ingrowth, acidifying the Cerenkov counted sample with HNO3, separating the 90Y using Sr Resin(Figure 1B) or DGA Resin (Figure 1C), and measuring 90Y by Cerenkov counting.
This method is not as rapid as the Cerenkov/LSC rapid 89/90Sr method, due to the 90Y ingrowth period.
However, due to the separation of pure 90Y from strontium and other beta emitting nuclides with high decontamination
factors, this method may provide more accurate and sensitive measurements for samples with high 89Sr/90Sr or90Sr/89Sr ratios. The chemical yield of Sr may be measured via stable strontium carrier by taking a small aliquot of theseparated strontium fraction for analysis by ICP-MS or ICP-AES or by 85Sr gamma emission. Yttrium yields may also be
tracked using stable Y and measurement by ICP-MS or ICP-AES.
6U E\ *)3& < E\ *)3& )ROORZLQJ ,QJURZWKDQG 6HSDUDWLRQ Total 89/90Sr can be measured
effectively using low background gas flow proportional counting (GFPC) following separation of strontium on Sr Resin(Figure 1A) [4,5]. Prior to measurement by GFPC, purified strontium fractions are dried onto cupped planchets or
precipitated as carbonates or phosphates and collected on filter paper (and dried). Immediate counts of the purified
strontium fractions yield the total radiostrontium (89Sr + 90Sr). Following the initial count for total radiostrontium and aperiod of 90Y ingrowth, the dried sample can be dissolved from the planchet or filter using HNO3, and additional
separations performed to isolate 90Y from the strontium fraction using Sr Resin (Figure 1B) or DGA Resin (Figure 1C).
90Y can then be measured by GFPC after evaporation on a stainless steel planchet or collection of an YF3 precipitate ona filter. 90Sr activity can be calculated using the measured 90Y activity and the period of ingrowth from the initial
separation. 89Sr activity can be calculating by difference (total radiostrontium - 90Sr).
When using GFPC, strontium chemical yield may be determined via stable strontium using ICP-MS, ICP-AES orgravimetric methods. Additionally, multiple drawer GFPC systems allow for the simultaneous counting of multiplesamples, an option which is normally not available for Cerenkov or LSC.
5HIHUHQFHV
1) Ohno, T., Hirono, M., Sakata, S., “Determination of Strontium 90 in environmental samples by triple quadrapole ICPMS and its application to Fukashima soil samples.” J. Anal. At. Spectrom. 33, 1081-1085 (2018).
2) EPA 402-R-10-001d, “Rapid Radiochemical Method for Total Radiostrontium (Sr-90) In Water for Environmental
Remediation Following Homeland Security Events,” October 2011.
3) Banavali, A. D. et al. "Strontium-89, 90 Analysis by Eichrom Column Chemistry and Cerenkov Counting". 38th Annual
Conference on Bioassay Analytical and Environmental Radiochemistry. Santa Fe, NM. November 1992.
4) ASTM D5811-08, “Standard Test Method for Strontium-90 in Water.”5) IAEA Analytical Quality in Nuclear Applications Series No. 27. “Rapid Simultaneous Determination fo 89Sr and 90Srin Milk: A Procedure Using Cerenkov and Scintillation Counting,” IAEA/AQ/27 (2013). https://www-pub.iaea.org/MTCD/
Publications/PDF/IAEA-AQ-27_web.pdf
6) Maxwell, S.L.; Culligan, B.K.; Hutchinson, J.B.; Utsey, R.C.; McAlister, D.R.; “Rapid Determination of 90Sr in Seawater
Samples,” J. Radional. Nucl. Chem., 303, 709-717 (2015).

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