Instrumentation & Methods:
Strontium 89, 90
Lynn West
Wisconsin State Lab of Hygiene
Method Review
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Strontium 89, 90
z
EPA 905.0, SM 7500-Sr B
Radiochemical Characteristics
Isotope T1/2
Decay
Mode
89Sr
50.55 days
Beta
MCL
pCi/L
80
90Sr
29.1 years
Beta
8
90Y
64.2 hours
Beta
N/A
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Strontium (EPA 905.0, SM 7500-Sr B)
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Prescribed Procedures for
Measurement of Radioactivity in
Drinking Water
EPA 600 4-80-032
August 1980
Standard Methods 17th, 18th, 19th &
20th
Strontium Chemistry
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Chemically similar to Ca
+2 oxidation state in solution
Insoluble salts include: CO3 & NO3
“Real Chemistry”
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Interferences
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Radioactive barium and radium
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Precipitated as carbonate
Removed using chromate precipitation
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Non-radioactive strontium
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Calcium
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Cause errors in recovery
Precipitated as carbonate
Removed by repeated nitrate
precipitations
905.0 Method Summary
Isolate Strontium
{ Measure total strontium
{ Allow strontium to decay
{ Isolate strontium 90 daughter –
yttrium 90
{ Measure yttrium 90
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905.0 Method Summary
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1 L acidified sample
Isolate Strontium
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Add stable Sr carrier
Precipitate alkaline and rare earths as
carbonate
Re-dissolve
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905.0 Method Summary
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Isolate Strontium(continued)
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Precipitate as nitrate
Re-dissolve
Precipitate as carbonate
Determine chemical yield
905.0 Method Summary
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Measure total strontium activity
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Determine
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90Sr
Yttrium in growth – 2 weeks
Isolate yttrium
Determine 90Y
905.0 Method Summary
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Determine 89Sr
z Calculated
z Total strontium minus
90Sr
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905.0 Method Summary
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Calculations include
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Recovery correction
In-growth correction – yttrium
{ Total
strontium
90
{ Strontium
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Decay correction – yttrium
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Isolation of Y to end of count time
Calculation total strontium
Total strontium activity (D)
D = C / 2.22*E*V*R
where:
C = net count rate, cpm
E = counter efficiency for 90Sr
V = sample volume, liters
R = fractional chemical yield
2.22 = conversion factor dpm/pCi
Calculations cont.
{ See
handout
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Calculations cont.
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Verify computer programs
Decay constants and time intervals
must be in the same units of time
Minimum background count time
should be equal to the minimum
sample count time
Instrumentation
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Low background gas flow
proportional counter
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P-10 counting gas (10% CH4 & 90%
Ar)
Due to in growth and short half-life
of 90Y, time is critical
Instrument Calibration
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Isotope specific calibration
z 89Sr
z 90Sr
z 90Y
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Use NIST traceable standards
Perform yearly or after repairs
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Quality Control
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Batch Precision:
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Sample duplicate OR
Matrix spike duplicate
Calculate relative percent difference
Calculate control limits
Should be < 20%
Frequency 1 per 20
Quality Control, continued
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Batch Accuracy
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Laboratory fortified blank
Matrix spike sample
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2 – 10 Xs detection limit
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Reagent background
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Instrument drift
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|reagent background|< detection limit
Quality Control, continued
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Daily control charts
Acceptance limits
Corrective action
Preventative maintenance
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