The Determination of 224Ra, 226Ra, & 228Ra in Water Samples
Michael Fern
Eichrom Technologies, Inc.
Background
• EPA monitoring of radium in water in US
• Ra-224 found in drinking water in New Jersey
• Need for faster method to measure Ra-224
• ASTM + US Geological Survey
1 2
Load sample in 0.095M HNO3
Rinse 0.095M HNO3
1
2
3 0.35M HNO3
3
3
Ln
Resin
1
20.5-2 L acidified sample
Ba-133
BaSO4 ppt
Conversion to BaCO3
{hold for ~30 hrs.}
0.095M HNO3
-ray measurement Ba-133
228Ra via 228Ac
{proportional or HPGe counter}
226Ra via Rn emanation
223,224Ra via -spectrometry
Original Method – Eichrom RAW01(Burnett, et al., 1995)
228Ra Results Burnett, et al. 1995
Sample Expected Result
Bq/L
Experimental Result
Bq/L
EMSL Ra/H2O
17 July, 19920.618 ± 0.122 0.651 ± 0.026
EMSL 228Ra Standard 2.19 ± 0.08 2.24 ± 0.05
Decontamination
Experiment1.10 ± 0.04 1.17 ± 0.02
EMSL Performance Eval. 19 April, 1994
0.744 ± 0.185 0.799 ± 0.044
Limitations of Original Method
• α-emitters determined by Rn emanation: too long
• Need fast method to measure 224Ra (t1/2 = 3.66 days)
• 30 hour ingrowth for 228Ac
• Conversion of SO42- to CO3
2- is tedious
New Approach - RAW03
Load sample in 0.095M HNO3
Rinse 0.095M HNO3
1
2
3 0.35M HNO3
Ln•
Resin
1
3 21
3
2
228Ra via 228Ac
{proportional or HPGe counter}
224, 226Ra via -spectrometry1
2
32
1
3
Cation
Resin
Ln
Resin
1
2
3
Load sample at pH 2 (0.5 – 1 L)
Rinse 50 mL 0.1M HNO3
50 mL 8M HNO3
Evaporate and re-dissolve in 0.095M HNO3
To waste
Advantages of New Method
• No need for 228Ac ingrowth
• Eliminate dangerous and inconsistent carbonate conversion
• Rapid measurement of α-emitting isotopes
• Same day measurement of 224Ra
226Ra % Recoveries-0.5L DI Water
0102030405060708090
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sample #
Eichrom data
226Ra Alpha Spectrum
226Ra, 224Ra, and Daughters
226 Ra222Rn
224Ra
218Po220Rn
226Ra % Recoveries in Tap water
0
20
40
60
80
100
120
1 2 3 4 5
Sample #
4 Tap Water (0.5L)5 Tap Water (1.0 L)
Eichrom data
226Ra in EPA SampleSept.18, 1998
Sample # Ba-133 % Yield
Eichrom mBq/L
1 89 57.7
2 100 45.5
3 98 53.6
Average 95.7 + 6 52.2 + 6.3
Expected EPA Value
62.9 + 18.5
Eichrom data
226Ra in NJ Sample
Sample # Ba-133 % Yield
Eichrom mBq/L
1 100 326 + 36
2 82 337 + 44
Average 91 320 + 37
Expected NJ Value
- 337 + 18
Eichrom data
226Ra in Georgia Inst. Of Tech. Sample# S8933
Sample # Ba-133 % Yield
Eichrom mBq/L
S8933
88
836 + 110
Expected Value
-
665 + 74
Eichrom data
226Ra in Georgia Inst. Of Tech. Sample# WS 14776
Sample # Ba-133 % Yield
Eichrom mBq/L
WS 14776
88
153 + 21
Expected Value
-
122 + 11
Eichrom data
226Ra Results Herbert, USEPA 2002
Sample Chemical recovery(Ba-133)
SpikedpCi/L
(mBq/L)
Found pCi/L
(mBq/L)
A 92.8% 1.16(42.9)
1.22(45.1)
B 87.1% 5.80(215)
5.73(212)
C 84.3% 11.6(429)
11.7(433)
228Ra ResultsHerbert, USEPA 2002
Sample Chemical recovery(Ba-133)
SpikedpCi/L
(mBq/L)
Found pCi/L
(mBq/L)
A 92.8% 32.8(1210)
32.0(1180)
B 87.1% 10.9(403)
11.9(440)
C 84.3% 4.37(162)
4.54(168)
Ca and Mg Interference in 500 mL Samples
Effect of Ca & Mg on Ra-226 Recoveries
75%61%
54%
0.00% 0.00%
87% 82%71% 70% 74%
0%
20%
40%
60%
80%
100%
0.00 100.00 200.00 600.00 1000.00
Ca & Mg ppm
% R
a-22
6 Ca PPM
Mg PPM
Eichrom data
Ca Interference in 100 mL of Sample
Effect of Ca on Ba-133 and Ra-226 Recoveries100 mL Sample
99% 99%97%
101%
90%
97%99%
95%
103%
87%
75%
80%
85%
90%
95%
100%
105%
100.00 200.00 300.00 400.00 500.00
Ca ppm
% B
a-13
3/R
a-22
6
Ba-133
Ra-226
Eichrom data
Detection Limits – 226RaUS EPA Requires: 37 mBq/L
Sample volume
Count Time
Detection. Limit
0.5 L 1000 min 3.3 mBq/L
0.5 L 240 min 11.1 mBq/L
0.2 L 240 min 33.3 mBq/L
0.1 L 480 min 33.3 mBq/L
Summary
• <37 mBq/L detection limits achievable
• Eliminates inconsistent carbonate conversion
• Faster measurement of 224Ra
• High amounts of Ca and Mg interferences handled well with 100 mL samples
• Acceptable 226Ra and 228Ra recoveries
Special thanks to:
Anil Thakkar, Eichrom Technologies David McCurdy & Ann Cleveland, ASTMDr. B. Parsa, New Jersey department of health, NJDr. B. Kahn, Georgia Institute of Technology, GA
References:
Burnett, W.C., Cable, P.H., & Moser, R.; Determination of Ra-228 in Natural Waters Using Extraction Chromatography, Radioactivity & Radiochemistry, vol. 6, no. 3 (1995)
Herbert, V., USEPA NAREL, Single Operator Test Report, ASTM Test Method: Ra in Water; presented at RRMC, Knoxville, TN 11/2002.