2.6.9 - Ni-63 by Extraction Chromatography

Introduction

⁶³Ni (T_1/2 = 101.2 a) is formed by neutron activation of stable ⁶²Ni in the primary coolant circuit of a nuclear reactor as a pure low energy β-emitter. Therefore, it has to chemically be separated from the matrix and interfering radionuclides before its determination. One of the most useful methodologies makes use of its property to precipitate as Ni-dimethylglyoxime (DMG) either by applying the classical procedure or by extraction chromatography on a DMG coated solid support such as microethene.

Eichrom provides the material as "Ni resin". ⁶³Ni can directly be measured by LSC after its elution from the column without further treatment.

Materials and Equipment

• ⁶³Ni standard and 1 mg stable nickel as carrier (without HNO₃)

• Niresin (Eichrom, TrisKem)

• 0.2 M ammonium citrate solution (pH 8-9)

• Basic buffer solution (100 mL water + 1 mL 1 M ammonium citrate solution, adjusted to pH ≈ 9 with NH₄OH)

• 3 M HNO₃

• Gelating LS cocktail (e.g. Quicksafe A)

For Classical Procedure:

• Fe³⁺ salt

• 6 M NH₄OH

• Dimethylglyoxime

• 1 M HCl

Procedure

(according to NIW01 [Eichrom 2003], see also [Langer 2000])

1. Precondition the Ni column by draining with 5 mL of basic buffer solution

2. Transfer the sample onto the column and wash twice with 5 mL 0.2 M ammonium citrate solution; a red band will appear on the column

3. Elute Ni with a minimum amount of 3 M HNO₃ (red band should disappear)

4. Transfer an aliquot of the solution into a LSC vial and mix with gelating cocktail

5. A part of the eluate can be used for yield determination (e.g. by ICP-MS).

Classical Procedure ([Resl 1999] and others)

The classical procedure avoids the commercially available EICHROM resin by precipitating Ni directly as dimethylglyoxime (DMG). The whole procedure consists of

1. Separation of radioactive Ni and the added Ni carrier by Fe hydroxide precipitation

2. Further purification by several DMG precipitations

3. Heating the purified Ni to form black Ni oxide; this is weighed to measure the chemical yield of the process.

4. Dissolution of Ni oxide with 1 M HCl and LS counting after addition of a gelating cocktail 

Evaluation

The activity of ⁶³Ni is calculated according to the general procedure. Chemical quench correction and in case of colorization as well color quench correction should be employed. If Actinides are present, they should be separated before head e.g. by Iron / Nickel hydroxide precipitation at pH 7 to 8.

Details of the classical procedure can be found in [Resl 1999] or in a suitable handbook for analytical chemistry. This method is applicable for most aqueous samples including those containing organic complexing agents. When Nickel is complexed by organic compounds such as EDTA, these must be destroyed to obtain quantitative precipitation of Ni as dimethylglyoxime.

Lower Limit of Detection LLD: about 40 mBq per sample, but lower with preconcentration

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

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

RESL 1999: Technical Procedure CHEM-TP-Ni.1, Determination of ⁶³Ni in water