Analytical Procedure

IRON-55 IN WATER
1. SCOPE
1.1.

This is a method for the measurement of Iron-55 in water samples.

1.2.

This method does not address all aspects of safety, quality control,calibration or instrument set-up. However, enough detail is given
for a trained radiochemist to achieve accurate and precise results
for the analysis of the analyte(s) from the appropriate matrix, whenincorporating the appropriate agency or laboratory safety, quality
and laboratory control standards.

2. SUMMARY OF METHOD
2.1.

Iron-55 is preconcentrated from water samples using a ferrichydroxide precipitation and separated using Eichrom's TRU Resincolumn. Up to 2.5mg of stable iron carrier can be added to thesample, as a yield monitor. Once the iron fraction is separated,iron recovery can determined from a batch yield sample, fromchemical recovery of stable iron via atomic emission spectrometryor gravimetrically as an iron hydroxide precipitate. Fe-55 ismeasured by liquid scintillation counting.

3. SIGNIFICANCE OF USE
3.1.

This is a rapid, reliable method for measurement of Fe-55 in water
samples that is more cost-effective and efficient than traditional
techniques.

4. INTERFERENCES
4.1.

The maximum amount of iron to be loaded on a 2mL prepacked
TRU column is 2.5mg. Samples with high iron content must be
aliquotted appropriately, so that the 2.5mg of Fe/sample is notexceeded.

5. APPARATUS


Analytical balance, 0.0001 g sensitivity
Beakers, glass
Centrifuge, with rotor and carriers for 50mL and 250mL tubes
Centrifuge tubes, 50mL and 250mL

Eichrom Technologies, LLC
Analytical Procedure
May 1, 2014

Method No: FEW01
Revision: 1.1
Page 1 of 7Column rack, Eichrom Part: AC-103
Vacuum filter apparatus
Extension funnels, 25 mL, Eichrom Part: AC-120
Filter, 0.45micron
Fume hood
Liquid scintillation counter
Liquid scintillation vials
Tweezers

6. REAGENTS
Note: Analytical grade or ACS grade reagents are recommended. Evaluation of key reagents,
such as aluminum nitrate and ammonium hydrogen phosphate, for contribution to method
background levels from naturally occurring radioactive materials is recommended.
Sodium hydroxide, NaOH
Deionized water, All reagents are prepared using deionized water
Ferric nitrate, Fe(NO3)3·9H2O
Isopropyl alcohol, C3H7OH
Nitric acid (70%), concentrated HNO3Phenolphthalein pH Indicator
TRU® resin, 2mL prepacked column, 100-150µm, Eichrom Part TR-C50-A
6.1.

Iron carrier - (5mg/mL Fe) - Dissolve 3.6g of Fe(NO 3 ) 3 ·9H 2 O in
80mL of water. Dilute to 100mL with water.

6.2.

Phenolphthalein solution - dissolve 1g phenolphthalein in 100mL
95% isopropyl alcohol. Dilute with 100mL of water.

6.3.

Nitric acid (2M) - Add 125mL of concentrated HNO 3 to 700mL ofwater. Dilute to 1L with water.

6.4.

Nitric acid (8M) - Add 500mL of concentrated HNO 3 to 400mL ofwater. Dilute to 1L with water.

6.5.

Nitric acid (0.5M) - Add 31mL of concentrated HNO 3 to 400mL ofwater. Dilute to 1L with water.

6.6.

Sodium hydroxide (1M) - Add 20g of NaOH to 400mL of water. Mixto dissolve. Dilute to 500mL with water.

Eichrom Technologies, LLC
Analytical Procedure
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Method No: FEW01
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6.7.

Sodium hydroxide (4M) – Add 80g of NaOH to 400mL of water. Mixto dissolve. Dilute to 500mL with water.

7. PROCEDURE
7.1.

Preconcentration of Fe-55 by ferric hydroxide precipitation

7.1.1. If necessary, filter water sample using 0.45m filter to remove
particulates.
7.1.2. Acidify water samples of up to 1L to pH 2 using concentrated
HNO 3 .
7.1.3. To each water sample, add 0.75mL of phenolphthalein indicator,
and 0.5 mL of 5mg/mL Fe carrier.
Note: Fe is added as a yield monitor and to preconcentrate Fe‐55 using a ferric hydroxideprecipitation.
7.1.4. Mix samples thoroughly and heat to 60-80 o C for 15-20 minutes.
7.1.5. Allow samples to cool to room temperature.
7.1.6. While stirring, slowly add enough 1M NaOH to reach the pinkphenolphthalein indicator endpoint.
Note: NaOH should be used to adjust the pH. Adjusting the pH with NH4OH can lead to lower
recoveries of iron during the ferric hydroxide precipitation.
7.1.7. Allow precipitate to settle until supernate can be decanted orproceed to next step and centrifuge samples for quicker
separation.
7.1.8. Transfer samples, including precipitate to 250mL centrifuge
tubes. Centrifuge samples at 2000rpm for 10-20 minutes.
Decant supernate. Repeat until entire sample has beentransferred to centrifuge tube and centrifuged.
7.1.9. Rinse sample beaker with 10mL of deionized water. Transfer
rinse to the appropriate centrifuge tube. Centrifuge samples for
10 minutes at 2000rpm. Decant supernate.
7.1.10. Dissolve precipitate in 5mL of concentrated HNO 3 .
7.1.11. Transfer dissolved samples to 15mL centrifuge tubes.
7.1.12. Rinse 250mL centrifuge tubes with 5mL deionized water.
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7.1.13. Transfer rinses to the appropriate 15mL centrifuge tubes. Cap15mL centrifuge tubes and mix.
7.2.

Iron separation using Eichrom TRU Resin column

7.2.1. For each sample, place a TRU Resin column in the column rack.
Attach a column reservoir to each column.
7.2.2. Place a beaker or a waste tray below each column. Remove thebottom plug from each column and allow to drain.
7.2.3. Add 5mL of 8M HNO 3 into each column reservoir. Allow solution
to drain through columns.
7.2.4. Load sample in 8M HNO 3 on the column. Allow solution to passthrough column.
7.2.5. Rinse sample centrifuge tubes with 5mL 8M HNO 3 . Add tube
rinse to column reservoir. Allow solution to pass throughcolumn.
7.2.6. Rinse the column with 10mL of 8M HNO 3 . Allow solution to passthrough column.
7.2.7. Place a clean, labeled 50mL centrifuge tube below eachcolumn. Elute Fe with 15mL of 2M HNO 3 .
7.2.8. Slowly add 4M NaOH until ferric hydroxide precipitate forms (pH4-9).
7.2.9. Determine Fe yield using a batch recovery sample, atomicemission spectrometry (Steps in 7.3.) for stable iron or
gravimetric recovery of stable iron (Steps in 7.4.).
7.3.

Iron recovery by atomic emission spectrometry

7.3.1. Centrifuge at 2000rpm for 5-10 minutes.
7.3.2. Decant supernate.
7.3.3. Dissolve sample in 5mL of 0.5M HNO 3 .
7.3.4. Remove a 0.25mL aliquot of each sample from step to a 10mL
volumetric flask for stable iron yield analysis by atomicemission spectrometry.
7.3.5. Dilute yield sample aliquot to 10mL with 0.5M HNO 3 .
7.3.6. Analyze sample for iron using atomic emission spectrometry.
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7.3.7. Transfer remaining sample to a 20mL liquid scintillation vial.
7.3.8. Add 15mL of liquid scintillation cocktail.
7.3.9. Measure Fe-55 using liquid scintillation counting.
7.4.

Iron recovery by gravimetric determination of stable iron7.4.1. Filter the solution from 7.2.7 through a 25mm diameter glass
fiber filter using a filter apparatus.
7.4.2. Dry the filter under a heat lamp completely.
7.4.3. Weigh the filter and record the weight.
7.4.4. Place the glass fiber filter in a 20mL liquid scintillation vial.
7.4.5. Add 15mL of liquid scintillation cocktail and count Fe-55 using aliquid scintillation counter.
8. CALCULATIONS
Atomic Emission Spectrometry Recovery of Fe Carrier.

where:Cmeas=

7.5 ppm =concentration in ppm measured by atomic emission spectrometryTheoretical concentration in ppm for 3 mg stable Fe, 0.25mL
aliquot of 5.0mL total, diluted to 10mL.

Gravimetric: Fe carrier

Yield =( Rw  Tw  Bw )Cw

where:
Rw=

residue+filter, mg

Tw=tare weight of filter, mg

Bw=blank weight, mg (extractant loss from column)

Eichrom Technologies, LLC
Analytical Procedure
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Method No: FEW01
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Cw=

Expected FeOH, mg (This is the wt. of Fe carrier added and thenconverted to FeOH equivalent wt.)

Fe-55 activity.

where:A =S =B =
E =
V =
Y =
60 =

Fe-55 sample activity (Bq/L)
Fe-55 measured activity, cpm
blank activity, cpm
counting efficiency
sample volume, liters
Fe-carrier yield
Conversion from cpm to cps

9. REFERENCES

1)

E Philip Horwitz, Renato Chirizia, Mark L. Dietz, Herbert Diamond, andDonald M. Nelson. Separation and Preconcentration of Actinides fromAcidic Media be Extraction Chromatography. Analytica Chimica Acta, 281(1993) 361.

2)

Pacific Northwest Laboratory Method PNL-ALO-345, Iron-55 Analysis

3)

ASTM Method D49922-09, “Standard Test Method for the determination ofradioactive iron in water.”

Eichrom Technologies, LLC
Analytical Procedure
May 1, 2014

Method No: FEW01
Revision: 1.1
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Eichrom Technologies, LLC
Analytical Procedure
May 1, 2014

Method No: FEW01
Revision: 1.1
Page 7 of 7