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.