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 and 90Sr. Stable strontium or 85Sr may also be used as a chemical yield tracer. Methods typicallybegin with a concentration or matrix removal step, followed by the separation of strontium from interfering nuclides(Figure 1). Methods may also incorporate steps to discriminate between 89Sr and 90Sr, including multiple counts, nuclide
selective counting techniques and ingrowth and secondary 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, taking into account process
knowledge, available measurement equipment and data quality objectives (required detection limits, urgency ofmeasurement, age of sample, and need for 89/90Sr discrimination). The measurement methods are meant be to used inconcert 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 can also be found in references [2] and [5].
Table 1. Summary of 89/90Sr Method Options
Primary
Separation

MethodICP-MS
Total 89/90Sr

1A1A901CY Direct8990

Two Count Sr and Sr
8990

89

90

Rapid Sr and Sr
90Cerenkov Sr and Sr( Y)
Gas Flow Porportional

PrimaryCount

SecondarySeparation

SecondaryCountSr 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

3,585

3,54,590
89/90
90

1A

89/90

1A

89

1A
1A

89

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 counts

NuclideHalf-Life

Decay
Mode8564.849 days

e/g

Sr

88

Sr89

Sr90

Sr90

Y

Stable50.563
bdays
28.79 years

b-64 hours

b-Table 2. Properties of Selected Nuclides
Detector Suitable for Measurement
EnergyGFPCLSC
Cerenkov MS/AES Gammag = 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

NoYes

NoNoYes

NoNo

NoYes

NoYes

Yes

Yes

NoNoYes

Yes

NoYes

NoYes

Yes

Yes

NoNo

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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.
(5) Rinse Sr Resin sequentially with*- 3 bed volumes 8M HNO3.
- 3 bed volumes 3M HNO3 - 0.05Moxalic acid.
- 3 bed volumes 8M HNO3.
(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. notes
for recommended rinsing for each matrix.

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Sr Resin
2 mL cartridge

DGA Resin, Normal
2 mL cartridge(1) Dissolve Sr Residue from planchet
used for total 89/90Sr measurementwith 5 mL 8M HNO3.
(Or acidify Cerenkov sample to
8M HNO3.)(1) Dissolve Sr Residue from planchet
used for total 89/90Sr measurementwith 5 mL 8M HNO3.
(Or acidify Cerenkov sample to
8M HNO3.)(2) Using transfer pipet, transfer
dissolved residue to 15mL ctube.
(3) Rinse planchet with 5 mL
8M HNO3. Add to 15 mL c-tube.

(2) Using transfer pipet, transfer
dissolved residue to 15mL c- tube.
(3) Rinse planchet with 5 mL
8M HNO3. Add to 15 mL c-tube.
(4) Precondition 2 mL DGA Resin
cartridge with 5 mL 8M HNO3.
(5) Load sample at 1-2 mL/min.

(4) Precondition 2 mL Sr Resin
cartridge with 5 mL 8M HNO3.
(5) Load sample at 1-2 mL/min,collecting eluate (90Y-fraction).
(6) Rinse c-tube with 5 mL 8M HNO3.

(7) Add tube rinse to column.
Elute 1-2 mL/min, collectingeluate (90Y fraction)(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.

,&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 limitwill 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 (<1mgvs 4-6 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 from
89Sr 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 fresh
fission products, such as 91Y and rare earth radionuclides, will cause significant positive bias in the 90Sr
determination performed using this method. Stable yttrium yield can be measured by ICP-MS or ICP-AES.
7ZR &RXQW 0HWKRG    90Sr and/or 89Sr 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, andindividual 89Sr and 90Sr activities calculated by solving a series of equations related to the decay of 89Sr and theingrowth of 90Y (two count method) [2]. Ideally, the initial count is performed as quickly as possible following theseparation on Sr Resin to minimize 90Y ingrowth. The second count is ideally performed after 1-2 weeks of 90Yingrowth. 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 Cerenkovcounting (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 byLSC 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 byLSC 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.
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 is recommended, as the Sr can be effectively rinsed from the column, while 90Y recovery remains
essentially 100% (k’ Y on DGA >>1000). In high 89Sr/90Sr samples, small breakthrough of strontium from separation onSr Resin into the 90Y fraction (k’ Sr only ~100 on Sr Resin) can lead to high bias of the 90Sr measurement and acorresponding low bias of the 89Sr.
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    90Sr and/or 89Sr can bemeasured 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 planchetsor 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. GFPC offers relatively high detection efficiency and very low instrument background and,
therefore, normally the lowest detection limits of the available counting techniques. Additionally, multiple drawer
GFPC systems allow for the simultaneous counting of multiple samples, an option which is normally not available for
Cerenkov or LSC.
5HIHUHQFHV1) Feuerstein J, Boulyga S.F., Galler P., Stingeder G., Prohaska T., “Determination of 90Sr in soil samples using
inductively coupled plasma mass spectrometry equipped with dynamic reaction cell (ICP-DRC-MS).” J. Environ.
Radioact. 11, 1764-9 (2008).
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) Eichrom Method SRW01VBS, “Strontium-89/90 in Water,” http://www.eichrom.com/eichrom/radiochem/methods/eichrom/index.aspx.
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).
1955 University Lane Lisle, IL 60532, USA+1 (630)963-0320

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