Extraction Chromatography on columns was first introduced in the 1970th, but it has found now a broader application ever since materials as powder or in prepared columns are commercially available from EICHROM Ind. [Horwitz et al. 1992]. Among the various available products (table 7), the Strontium SPEC is probably the mostly applied column.
Due to their similar ionic radius, both Sr2+ and Pb2+ as 2-valentic cations in HNO3 solution are retained on SPEC columns (EICHROM, TrisKem). Thus, they can easily be concentrated and separated from all other cations and from each other by the complexing affinity of Pb2+ with citrate.
The extraction chromatographic method described below is selective and rapid. The sample preparation procedure as preliminary step has to be selected according to the material to be analysed. The procedure below was adapted from Langer [Langer 2000] and [Horwitz 2010].
Table 6: Commercially available EICHROM extraction chromatographic columns
Materials and Equipment
- Sr SPEC column (EICHROM, Triskem)
- Sr, and Pb carrier solutions
- HNO3 (8 M, 6 M, 0.05 M)
- 0.1 M ammonium citrate (pH 5)
- Gelating cocktail (long range for citrate e.g. OptiPhase HiSafe III)
- The Sr-SPEC-column is preconditioned with 5 mL 8 M HNO3.
- The preconcentrated water sample in 8 M HNO3 is added onto the column.
- The column is washed with 5 mL 8 M HNO3 (separation of interfering elements e.g. 210Bi and 90Y). Note time, as this is the initiation of ingrowth of 90Y!
- The column is washed with 5 mL 6 M HNO3 (separation of 210Po). This step can be omitted in absence of 210Po.
- Elution of 90Sr: Sr is finally eluted with 10 mL 0.05 M HNO3 and collected in a plastic vial (mix well!).
- For counting, 5 mL eluate are mixed with 15 mL gelating cocktail and measured immediately (only 90Sr).
- Another 5 mL eluate might be evaporated to dryness on a counting plate using an IR-lamp (weight before evaporation!) and measured with a proportional counter.
- Elution of 210Pb: 210Pb is eluted from the column with 10 mL 0.1 M ammonium citrate (pH 5) (mix well!)
- For counting, 4 mL eluate are mixed with 16 mL gelating cocktail.
The 90Sr content is calculated from the net counting rates RN, the measuring efficiency ε and the chemical yield η according to
The chemical yield can be controlled by comparing the amount of Sr carrier with the mass of Sr(NO3)2. The total emission probability of the β-decay of both 90Sr and 210Pb is 100 %.
The 210Pb content is calculated according to the general scheme by taking into account the ratio between sample and total volume. For all measurements quench correction must be applied.
Lower Limit of Detection LLD without considering any preconcentration
for 90Sr : 50 mBq per sample
for 210Pb: 70 mBq per sample
Horwitz E.P., Chiarizia R. and Dietz M.L. 1992: A novel strontium-selective extraction chromatographic resin; Solvent Extr. Ion Exch. 10(2) (1992) 313-36
Langer M. 2000: Training Material Exercise P0005 “Extraktionschromatographie”, Research Center Karlsruhe / FTU