2.6.7 - Fe-55 by Extraction Chromatography

Introduction

⁵⁵Fe (T_1/2 = 2.75 a) is formed by neutron activation of stable ⁵⁴Fe and decays by electron capture to ⁵⁵Mn emitting low energy X-rays and Auger electrons. Due to the low energy X-rays, ⁵⁵Fe cannot be directly determined by non-destructive γ-ray spectrometry. Therefore, radiochemical sample separation and/or purification steps are required before counting. One of the most efficient methodology to separate the ⁵⁵Fe is chromatographic extraction by using prepared Eichrom TRU resins, in which the CMPO (octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide) is dissolved in TBP (tri-n-butyl phosphate) and then employed to extract the Fe(NO₃)₃ [Warwick and Croudace 2006].

Materials and Equipment

• Stable Fe carrier (< 3 mg per sample)

• Standard solution of ⁵⁵Fe and ⁵⁹Fe as tracer

• TRU resin column (prepacked 100-150μm particle size, EICHROM)

• 8 M HNO₃; 2 M HNO₃

• Conc. HF

• Gelating cocktail

Procedure

(according to FEW01 [Eichrom 2003], see also [Langer 2000] and [Horwitz 1993])

1. Add 5 mL of 8 M HNO₃ into the TRU resin column for conditioning and allow draining

2. Add the aqueous sample in 8 M HNO₃ onto the TRU resin column

3. Rinse the column with 15 mL of 8 M HNO₃

4. Add 1 mL of 0.2 M HCl; allow draining and discard this fraction

5. Elute Iron with 15 mL of 2 M HNO₃ and homogenize the eluate

6. Transfer 5 mL of eluate into a measurement vial; carefully add 200 µL of conc. HF to decolorize and add 15 mL of gelating LSC cocktail for measurement

Evaluation

The activity of ⁵⁵Fe is calculated according to the general procedure. Chemical quench correction and in case of colorization as well color quench correction should be employed. The chemical yield is determined gravimetrically through the Fe carrier after precipitation as Fe(OH)_3, drying and weighing or, alternatively, radiometrically through ⁵⁹Fe activity added and recovered.

Lower Limit of Detection LLD: 100 mBq per sample, and lower with preconcentration

Eichrom Technologies 2003: NIW01 Rev 1.2, and FEW01 Rev. 1.0

Horwitz E.P., Chiarizia R., Dietz M.L., Diamond H. and Nelson D.M. 1993: Separation and preconcentration of Actinides from acidic media by extraction chromatography; Anal. Chim. Acta 281 (1993) pp 361

Langer M. 2000: Training Material Exercise P0005 “Extraktionschromatographie”, Research Center Karlsruhe / FTU

Warwick P.E and Croudace I.W. 2006: Isolation and quantification of ⁵⁵Fe and ⁶³Ni in reactor effluents using extraction chromatography and liquid scintillation analysis; Anal. Chem. Acta 567 (2006) 277–285