Acta Chim. Slov. 2005, 52, 297–302 297 Scientific Paper Tracer Studies on Sr Resin and Determination of 90Sr in Environmental Samples Rožle Jakopič and Ljudmila Benedik Department of Environmental Sciences, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, E-mail: rozle.jakopic@ijs.si Received 31-01-2005 Abstract In this work various tracer experiments were perf ormed to investigate the elution behaviour of some radionuclides on Sr resin, matrix effects of calcium and potassium and the resin capacity for strontium. None of the studied radionuclides interfered with the separation of strontium since ali were washed out with 3M HN03 before the elution step with water, except barium. Barium and strontium were separated using 8M HN03. The maximum resin capacity for strontium was 8.1 mg of Sr/g of Sr resin. Up to 2 g of calcium and 200 mg of potassium can be loaded on the Sr column (3 g Sr.spec) vvithout decrease in strontium recovery. The separation procedure using Sr resin was tested on soil samples spiked with 90Sr standard solutions and on reference materials. Ali results obtained by this method gave good agreement. Counting sources were prepared by vveighing SrC204 on a planchet. The 90Sr content was measured with a proportional gas flow beta counter after secular equilibrium betvveen 90Sr and 90Y was reached. The chemical recovery was determined gravimetricalh/ and was always higher than 80%. Key words: Sr resin, extraction chromatography, 90Sr, beta counting Introduction 90Sr is created in nuclear fission processes and it has been released to the environment with global fallout following atmospheric nuclear explosions, by nuclear waste discharges and by the Chernobyl nuclear power plant accident in 1986. 90Sr is radiotoxic because of its relatively long physical (28.6 y) and biological (49.3 y) half-life and because of chemical similarities with calcium. It accumulates mainly in bone tissues where its daughter 90Y radiates beta particles of relatively high end-point energy (Emax = 2.27 MeV).1 Both radionuclides 90Sr and 90Y are pure beta emitters with maximum energies of 546 keV and 2.27 MeV respectively, and they cannot be identified by direct measurements via gamma spectrometry. Procedures for determination of 90Sr are complicated and involve an extensive radiochemical separation before measurement to eliminate inactive and radioactive elements present in the sample that would interfere with subsequent beta counting. Among inactive interferences calcium is the most significant since it is similar to strontium and is present in environmental samples in large amounts.2'3 After separation and purification 90Sr is quantified by beta counting of the total activity of 90Sr and 90Y, after secular equilibrium is reached, with a proportional gas flow counter or by liquid scintillation. Different methods have been described in the literature for the determination of 90Sr. The oldest is the fuming nitric acid method, which relies on the better solubility of calcium nitrate in strong nitric acid compared to strontium nitrate. However, it involves numerous precipitation and filtration steps and is thus time consuming. Many other methods have been proposed that offer less aggressive conditions.4 These include liquid-liquid extraction3'5'6 and ion exchange.79 Recently, solvent extraction based on the macro-cyclic polyether 18-crown-6 for the selective extraction of strontium has been proposed, with different derivative compounds.1012 The resolution of strontium from other elements, particularly barium and calcium, was not satisfactory using liquid-liquid extraction as the only step for separation because of the low stability of crown ether complexes. Honvitz et al.1314 overcame this problem by development of a Sr resin (Sr.spec resin, Eichrom® Industries). The Sr resin consists of the crown ether 4,4'(5 ')-bis(tert-butylcyclohexano)-18-crown-6 dissolved in 1-octanol and sorbed on an inert polymeric support. It possesses the selectivity of solvent extraction and the ease of column chromatography. Many authors have reported methods using Sr resin for strontium separation in various environmental samples.1'21520 Procedures using Sr resin are simpler, shorter, result in higher recoveries and more reproducible results. Jakopič and Benedik Determination of 90Sr in Environmetal Samples 298 Acta Chim. Slov. 2005, 52, 297-302 The aim of this study was to study the behaviour of some radionuclides on Sr resin and to test the suitability of Sr resin for separation of strontium from solutions containing different amounts of potassium and calcium. Further, 90Sr in some reference materials was determined by the procedure developed by Vajda et al.20 which we slightly modified. Before the elution of strontium with deionised water a wash with 8M HN03 was added in order to separate strontium from barium completely and for the measurement a proportional gas flow beta counter was used instead of liquid scintillation. Experimental a) Materials and instrumentation Reagents: AH the reagents used were of analytical grade. Tracers: 85Sr 435.9 kBq g-1, (reference date: 30.11.2001), 133Ba 124.9 kBq g-1, (reference date: 30.4.1999) obtained from the Czech Metrological Institute, Czech Republic, 88Y 59.1 Bq g-1 (reference date: 9.12 2002) and 137Cs 58.7 Bq g-1 (reference date: 9.12.2002) obtained from LEA, France. 212Pb tracer was prepared from Th(N03)4-4H20 solution by extraction with dithizone in chloroform. A 90Sr/90Y standard solution of 48.2 Bq g-1 from LEA, France was used for spiking experiments. Samples: The reference materials IAEA 152 (milk powder), IAEA 154 (whey powder), IAEA 156 (clover), IAEA 375 (radionuclides in soil) and Soil-6 were analysed. Detectors: For gamma measurements an HP Ge Low Energy Photon Detector connected to a Canberra MCA by a Genie-2000 Softvvare multi-channel analyser system was used. For beta counting of 90Sr and 90Y a Berthold MULTI-LOGGER LB 5310 proportional gas flow beta counter was used. b) Sr column preparation The Sr columns were prepared by soaking approximately 3 g of Sr.spec (100-150 /jlui) chromatographic material in deionised water for 1 h and then packing it into a 20 cm long and 1 cm in diameter glass chromatographic column (Bio-Rad Laboratories). The column was washed with 100 mL of deionised water and pre-conditioned with 70 mL of 3M HNOj. For column regeneration 100 mL of deionised water and then 60 mL of 0.1M EDTA solution were passed through the column. c) Elution behaviour of Sr, Cs, Y, Ba and Pb 85Sr, 137Cs, 88Y, 133Ba and 212Pb tracers were added to a solution of 3M HN03. The solution was first measured on a gamma detector to determine the initial activity of each tracer and then loaded onto the top of the Sr column. The column was washed with nitric acid of different concentrations and with deionised water. Fractions were collected and measured on the gamma detector. The percentage of tracer in each fraction was determined relatively by comparison with the initial activity of each tracer. d) Calcium and potassium matrbc effects Solutions of 3M HN03 containing 85Sr tracer, 10 mg of Sr2+ carrier as Sr(N03)2 and different amounts of Ca2+ or K+ were prepared. The initial activity of 85Sr was measured on the gamma detector at 514 keV. The solution was loaded onto the Sr column, washed with 3M HN03 and the strontium was eluted with deionised water. Fractions were collected and measured on the gamma detector. The percentage of 85Sr in each fraction was determined relatively by comparison with the initial activity. e) Column capacity for Sr Solutions containing 85Sr tracer and 100 mg of Sr2+ carrier (in excess) in 20 mL of 3M HN03 were prepared. The solution was loaded onto the column (3 g of Sr.spec) and washed with 3M HN03. Fractions were collected and measured on the gamma detector. The percentage of 85Sr found in the water fraction was used for the determination of the column capacity for strontium. In each experiment the same Sr column was used. f) The stoichiometry of SrC204 Solutions containing 85Sr tracer, 10 mg of Sr2+ carrier and 10 mg of Ca2+ carrier in 3M HN03 were passed through the Sr column. The strontium in the water fraction was precipitated as strontium oxalate (see section h) below), filtered on a weighed filter paper and dried. g) Sample preparation Soil and biological samples were dried at 105 °C and then ashed in a furnace at 550 °C. About 1-3 g of ash was then used for the analysis. To each sample, 10 mg of Sr2+ carrier as strontium nitrate was added for chemical recovery determination. Biological samples (1-3 g) were leached with up to 100 mL of 8M HN03 in a covered beaker on a hot plate with magnetic stirring. The leachant and the residue were separated by filtration through a 0.45 |am filter. For soil samples (1 g) total dissolution was used. The soil samples in Teflon® beakers were treated by repeated addition of 63% HN03, 40% HF and 37% HC1. First 5 mL of 63% HN03 were added and the solution was heated and evaporated to dryness. Next 5 mL of 63% HN03 and 5 mL of 40% HF were added. Again the solution was heated and evaporated to dryness. In the last step 5 mL of 63% HN03, 5 mL of 40% HF and 5 mL of Jakopič and Benedik Determination of 90Sr in Environmetal Samples Acta Chim. Slov. 2005, 52, 297–302 299 37% HC1 were added. After evaporation of the final solution to near dryness, 0.3 g of H3B03 was added and evaporated to dryness. The heating and the evaporation of the solutions were performed in an aluminium block at 220 °C. The final residue was converted to nitrate form by evaporating it twice with 3 mL of 63% HN03 dissolved in 100 mL of 1M HN03 and filtered through a 0.45 |am filter. h) Separation and determination of strontium20 The filtrate was then heated to boiling and approximately 5 g of oxalic acid were added. The pH of the solution was adjusted to 5.5-6 with addition of sodium hydroxide. Depending on the matrix composition, additional Ca2+ was sometimes added (up to 300 mg) in order to obtain the oxalate precipitate. The suspension was centrifuged in a 100 mL centrifuge tube for 10 min at 3000 rpm (Tehtnica Železniki). The oxalate precipitate was washed three times with 70 mL of deionised water. The oxalate was then destroved by evaporating it twice with 5 mL of 63% HN03. The residue was dissolved in 30 mL of 3M HN03 and loaded onto the Sr resin. After washing the column with 100 mL of 3M HN03 and 60 mL of 8M HN03, strontium was stripped from the column with 100 mL of deionised water and the time was noted. The water fraction was evaporated to about 20 mL and 200 mg of oxalic acid was added. Then the pH of the solution was adjusted to 9-10 with 25% NH3. The solution was boiled for 10 minutes and SrC202 began to form. After cooling the solution, the precipitate was centrifuged on a measuring planchet (19 mm in diameter), dried, weighed for recovery determination and stored for 90Sr/90Y equilibrium for at least 14 days. The beta activity was measured with a gas flow proportional beta counter. Results and discussion a) Elution behaviour of Sr, Cs, Y, Ba and Pb The determination of 90Sr in environmental samples requires its chemical isolation from ali interfering elements, especially alkaline and alkaline-earth elements. Among them calcium is extremely difficult to separate due to its similar chemical behaviour with strontium. These can cause three types of interference: firsth/ with determination of the chemical yield by gravimetry (Ca, Ba), secondly by mass absorption effects in the final precipitate during beta counting (Ca, Ba) and thirdly by radioactive interference in counting (40K, 137134Cs,140Ba). Figure 1 shows three elugrams describing the behaviour of 88Y, 137Cs, 133Ba, 212Pb and 85Sr on a Sr column, filled with 3 g of Sr.spec chromatographic material. The gravity flow rate was 1-2 mL min-1. Figure la shows the elution curves obtained when 88Y, 137Cs, 133Ba and 85Sr were loaded on the column in 3M HN03. Both caesium and yttrium were washed from the column in the first 60 mL of 3M HN03. This behaviour is due to the low distribution coefficient for caesium in 3M HN03 (KD ~ 101).13 Most of the barium, however, is retained by the column during the loading and initial rinsing, and eluted as a broad peak. It started to elute at 120 mL and was washed from the column after approximately 220 mL of 3M HN03, but some fraction of the barium appeared in the water eluate. Strontium eluted rapidh/ in the first 20 mL of deionised water. We further investigated the behaviour of strontium and barium, because they could not be separated completeh/ with a) 3M HN03 H20 60 - 20 40 60 80 100 120 140 160 180 200 220 240 260 volume (mL) b) 60 20 40 60 80 100 120 volume (mL) c) 20 40 60 70 80 90 110 130 150 170 190 210 230 volume (mL) Figure 1. a) Elution curves of 85Sr, 133Ba, 88Y and 137Cs on Sr resin column in 3M HNO3 as loading solution (3 g Sr.spec material in column ? = 1 cm, l = 20 cm, flow rate = 1–2 mL min–1). b) Elution curves of 85Sr and 133Ba on Sr resin column in 8M HNO3 as loading solution (3 g Sr.spec material in column ? = 1 cm, l = 20 cm, flow rate = 1–2 mL min–1). c) Elution curves of 85Sr and 212Pb on Sr resin column in 3 M HNO3 as loading solution. (3 g Sr.spec material in column ? = 1 cm, l = 20 cm, flow rate = 1–2 mL min–1). 80 40 0 80 20 0 3 M HNO HO 60 - 50 - 40 30 20 10 - 0 Jakopič and Benedik Determination of 90Sr in Environmetal Samples 300 Acta Chim. Slov. 2005, 52, 297–302 3M HN03 solution. This time strontium and barium were loaded on the column in 8M HN03 where the distribution coefficient for barium is minimal (KD ~ 6) and for strontium maximal (KD ~ 200).13 Elution curves are presented in Figure lb. Barium started to elute quickly, after the first 20 mL of 8M HN03 and was completeh/ removed after 80 mL of 8M HN03. Lhe barium peak was narrower compared to the peak in the elugram in Figure la and no barium was detected in the strontium fraction. Finally, strontium was eluted with deionised water. Lead showed a very high retention on the Sr column, even more than strontium. It has a high distribution coefficient in the whole interval of nitric acid concentrations (KD ~ 102-103).13 Figure le shows the elution curves of strontium and lead in 3M HN03. Lhe stripping solution was changed to deionised water and strontium and lead were sequentially eluted from the column. Lhe Sr column has sueh a strong affinity for lead that it was eluted after strontium and the interference of lead on strontium was minimal. b) Column capacity for strontium Lhe purpose of this experiment was first to find the maximum amount of strontium that can be loaded on the column and used for determination of the recovery of the radiochemical procedure, and to see if the column capacity changes when the column is used repeatedh/. Repeated sorptions and elutions of 85Sr tracer and Sr2+ carrier were made on the same column. Lhe results are presented in Figure 2. number of repetitions Figure 2. Dependence of the column capacity for strontium on the number of repetitions (3 g Sr.spec material in column O = 1 cm, l = 20 cm, flow rate = 1-2 mL minJ, average uncertainty = 8%). From the graph it can be seen that the column capacity decreased with use, but not linearh/. Lhe maximum capacity of the column for strontium was estimated to about 8.1 ± 0.5 mg of Sr per g of Sr resin. After the fourth repetition the capacity was only 3.2 ± 0.3 mg, which is 40% of the initial one. Lhis value is three times less than the value stated by the producer. Lhis feature could not be explained. A similar result (8.8 mg/g of Sr resin) was obtained by Lorres et al.18 Some authors believe that reason for the decrease is probabh/ due to decomposition and removal of the stationary phase from the column, as well as possible destruetion of the crown ether by the strong nitric acids used in the separation step.21 In praetice we used each column three times. c) Matrix effect Calcium has a small distribution coefficient in 3M HN03 (KD ~ 10~2)13 but can be present in large amounts in some samples. Lo test the effect of calcium on retention and recovery of strontium, solutions with varying amounts of calcium were loaded on the column in 3M HN03. Figure 3 shows the elution curves obtained in this experiment. In Figure 3a the amount of calcium ranged from 100-1200 mg. After approximately 100 mL of 3M HN03, the column was eluted with deionised water. Ali the strontium was found in water fraction and none was detected in 3M HN03 fraction. Lhen a higher concentration of calcium was again loaded in 3M HN03. Lhis is shown in Figure 3b. Lhis time the washing with 3M HN03 was prolonged (200 mL) in order to see if any strontium appeared in that fraction. In fact about 20% of strontium was found in 3M HN03 when the amount of calcium was 2500 mg. a) ? 102 ? 314 ? 505 D 745 D 901 ¦ 1196 b) 60 80 100 volume (mL) m 1517 D 1818 «2481 volume (mL) Figure 3. a) Elution curves of 85Sr with 10 mg of Sr2+ carrier and different amounts of Ca2+ carrier (100-1200 mg) in 3M HN03 solution (3 g Sr.spec material in column O = 1 cm, l = 20 cm, flow rate = 1-2 mL minJ, average uncertainty = 8%). b) Elution curves of 85Sr with 10 mg of Sr2+ carrier and different amounts of Ca2+ carrier (1500-2500 mg) in 3M HN03 solution (3 g Sr.spec material in column O = 1 cm, l = 20 cm, flow rate = 1-2 mL minJ, average uncertainty = 8%). 80 10 40 8 0 6 20 40 120 140 4 2 00 0 2 3 4 80 60 40 20 0 50 00 150 200 250 300 350 Jakopič and Benedik Determination of 90Sr in Environmetal Samples Acta Chim. Slov. 2005, 52, 297–302 301 In Figure 4 the effect of calcium matrix on strontium recovery is presented. Practically no change in recovery up to 2000 mg is observed. The recoveries ranged from 93-100%. When the calcium content was above 2000 mg, the recovery for strontium started to decrease and dropped to 40% for 2800 mg of calcium. 120 100 80 60 40 20 0 iMti l r ž 0 500 2500 3000 1000 1500 2000 mass of Ca2+ carrier (mg) Figure 4. Calcium matrix effect on strontium chemical recovery (average uncertainty = 8%). The same experiment was performed with potassium. Potassium, however, has a greater influence on strontium retention, as can be seen from elution curves in Figure 5. For up to 200 mg of potassium, strontium is detected only in the water fraction. Some strontium is detected in 3M HN03 but this is due to experimental error. The recoveries for strontium were 96-100%. When higher amounts of potassium were loaded on the column, some losses of strontium occured during the washing with 3M HN03. The recoverv was 88% for 240 mg of potassium and 40% for 940 mg of potassium. D 11 ¦ 114 «237 B665 ? 941 60 40 20 0 20 40 60 80 100 120 140 volume (mL) Figure 5. Elution curves of 85Sr with 10 mg of Sr2+ carrier and different amounts of K+ carrier (10-1000 mg) in 3M HN03 solu-tion (3 g Sr.spec material in column O = 1 cm, l = 20 cm, flow rate = 1-2 mL minJ, average uncertaintv = 13%). When determining strontium in environmental samples losses of strontium can be expected due to matrix elements present, but this is accounted for by measuring the chemical recovery at the end of the radiochemical analysis. Separation from potassium is accomplished by oxalate precipitation, where potassium remains in solution. d) Recovery determination and the stoichiometry of SrC204 Chemical recovery in 90Sr determination was determined by weighing of SrC204 precipitate. We need to be sure that the precipitate has a stoichiometric composition to avoid errors in calculating the recovery and consequently the final result. The stoichiometry of the precipitate was checked by comparison of the gravimetric and radiochemical tracer recovery. The results are shown in Table 1. Table 1. Comparison between gravimetric and radiochemical recoverv of Sr on the same Sr column. Gravimetric recoverv SrC204 (%) Radiochemical recoverv (%) 85Sr 1 81.4 ± 0.9 79.9 ± 2.6 2 77.5 ± 0.8 76.3 ± 2.5 3 54.9 ± 0.6 54.1 ± 2.0 4 36.7 ± 0.4 36.3 ± 1.3 A good match between the gravimetric and radiochemical recoveries was found. The quotient of the gravimetric and radiochemical recovery was calculated and the average was found to be 1.015 ± 0.037. This result confirms the stoichiometry of the SrC204 precipitate. The decrease in recovery was due to the sequential decrease in the column capacity. e) 90Sr in some soil and biological samples Before analysing reference materials, we spiked six soil samples by addition of a 90Sr standard solution of a known activity. The solutions were left to stand overnight and analysed according to the analytical procedure described. The aim of this experiment was to study the effect of matrix elements on strontium determination. The activities of the added 90Sr ranged from 1-12 Bq and the masses of soil from 2-3 g. A good linear correlation betvveen the measured activity and the activity of the added 90Sr was obtained. The quotient was 1.0189 ± 0.01147. The R2 of linear regression analysis based on the method of least squares was 0.9988. Table 2. Comparison of 90Sr results obtained in reference materials with certified values. Sample This workc (Bq kg-1dry) Chem. recovery (%) Certified value (Bq kg-1dry) IAEA-152a 7.4±0.5 (2) 83.9±1.0 7.7±0.6 IAEA-154a 6.8±0.8 (3) 95.4±1.0 6.9±1.0 IAEA-156a 14.8±0.9 (3) 79.9±0.9 14.8±1.5 IAEA-375b 113±5 (4) 82.4±0.9 108±4 Soil-6b 28±4 (3) 80.9±0.9 30.3±6.5 a leaching. b total dissolution. c average ± lo standard deviation (number of determinations). The method was then tested by analysing several reference materials. The results obtained are compared to the reference values in Table 2. The activity of 90Sr in the sample was calculated by Equation (1). 120 Jakopič and Benedik Determination of 90Sr in Environmetal Samples 302 Acta Chim. Slov. 2005, 52, 297–302 ASr __________(R-Rb) 60-t-Tj-m-[eSr+er- [l-e-^ T ,( 1) where t is the counting time (min); r\ is the overall chemical recovery; m is the mass taken for the analysis (kg); eSr and eY are the counting efficiencies for strontium and yttrium, respectivelly; td is the time allowed for 90Y ingrowth (min); X is the decay constant of 90Y (min1); R is the count rate of the sample and Rb is the count rate of the background (min1). The background of the proportional gas flow counter was about 0.25 counts min-1. The uncertainty was given by Equation (2). ASr ¦ jtf + aj + al , a« (2) where a^ is the uncertainty of the chemical recovery; aL is the uncertainty of detector efficiency and aR is the uncertainty of the count rate of the sample. Good agreement was found in ali cases. The recoveries were always higher than 80%. Conclusions Our tracer studies showed that Sr resin can be successfulh/ used for separation of strontium from matrix elements and from interfering radionuclides. Among tested elements, only barium and lead were retained on the column. Barium was removed by washing the column with 8M HN03 while lead eluted after strontium due to its higher affinity. The main disadvantage is the low column capacity for strontium which is 8.1 mg/g Sr resin and decreases with use. This limits the reuse of the column. It was also shown that calcium and potassium had negative effects on strontium retention if the amounts were above 2 g for calcium and 200 mg for potassium for a column containing 3 g of Sr.spec chromatographic material. The results for 90Sr in reference samples were in good agreement with their certified values. Recoveries ranged from 80-95%. Acknowledgements This work was financially supported by Ministry of Education, Science and Šport of Slovenia (Project group Pl-0143, Cycling of nutrients and contaminants in the environment, mass balances and modelling of the environmental processes and risk analysis). References 1. F. Goutelard, R. Nazard, C. Bocquet, N. Coquenlorge, P. Letessier, D. Calmet, Appl. Radiat. Isot. 2000, 53, 145–151. 2. S. Brun, S. Bessac, D. Uridat, B. Boursier, J. Radioanal. Nucl. Chem. 2002, 253, 191–197. 3. I. Friberg, J. Radioanal. Nucl. Chem. 1997, 226, 55–60. 4. R. Bojanowski, D. Knapinska-Skiba, J. Radioanal. Nucl. Chem. Art. 1990, 138, 207–218. 5. H. Bem, Y. Y. Bakir, S. M. Shukerb, J. Radioanal. Nucl. Chem. 1991, 147, 263–268. 6. E. I. Shabana, K. A. Al-Hussan, Q. K. Al-Jassem, J. Radioanal. Nucl. Chem. 1995, 212, 229–240. 7. Z. Grahek, S. Lulić, K. Kosutić, I. Eskinja, S. Cerjan, K. Kvastek, J. Radioanal. Nucl. Chem. Art. 1995, 189, 141–146. 8. R. Stella, M. T. Ganzerli Valentini, L. Maggi, Appl. Radiat. Isot. 1990, 41, 905–908. 9. H. Amano, Y. Nobuyuki, Talanta 1990, 37, 585–590. 10. E. P. Horwitz, M. L. Dietz, D. E. Fisher, Solvent Extr. Ion Exch. 1990, 8, 199–208. 11. E. P. Horwitz, M. L. Dietz, D. E. Fisher, Solvent Extr. Ion Exch. 1990, 8, 557–572. 12. M. Pimpl, J. Radioanal. Nucl. Chem. Art. 1995, 194, 311–318. 13. E. P. Horwitz, R. Chiaritzia, M. L. Dietz, Solvent Extr. Ion Exch. 1992, 10, 313–336. 14. M. L. Dietz, E. P. Horwitz, R. D. Rogers, Solvent Extr. Ion Exch. 1995, 13, 1. 15. Ž. Grahek, N. Zečević, S. Lulić, Anal. Chim. Acta 1999, 399, 237–247. 16. A. Alvarez, N. Navarro, S. Salvador, J. Radioanal. Nucl. Chem. 1995, 191, 315–322. 17. C. Tieh-Chi, W. Jeng-Jong, L. Yu-Ming, Appl. Radiat. Isot. 1998, 49, 1671–1675. 18. J. M. Torres, M. Llaurado, G. Rauret, M. Bickel, T. Altzitzglou, R. Pilvio, Anal. Chim. Acta 2000, 414, 101–111. 19. M. Rodriguez, J. A. Suarez, A. G. Espartero, Nucl. Instr. And Meth. in Phys. Res 1996, 369, 348–352. 20. N. Vajda, A. Ghods-Esphahani, E. Cooper, P. R. Danesi, J. Radioanal. Nucl. Chem. Art. 1992, 162, 307–323. 21. P. Vreček, L. Benedik, B. Pihlar, Appl. Radiat. Isot. 2004, 60, 717–723. Povzetek Izvedli smo različne elucijske teste s sledilci, da bi raziskali obnašanje nekaterih radionuklidov na Sr koloni, določili kapaciteto Sr kolone za stroncij in matrični vpliv kalcija ter kalija na vezavo stroncija. Noben od proučevanih radionuklidov ni motil separacije stroncija, saj so se vsi razen barija sprali s kolone s 3 M HNO3. Barij in stroncij smo ločili z 8 M HNO3. Sr kolona prenese do 2 g kalcija in do 200 mg kalija, večje količine pa zmanjšajo izkoristek za vezavo stroncija. Metodo smo testirali z analizo prsti z dodatkom 90Sr in z analizo referenčnih materialov. Vsi rezultati so se dobro ujemali s certificiranimi vrednostmi. Izvor za merjenje smo pripravili s tehtanjem SrC2O4 na ploščico. Vsebnost 90Sr smo določili z merjenjem s pretočnim beta števcem po vzpostavitvi sekularnega ravnotežja med 90Sr in 90Y. Izkoristek postopka smo določili gravimetrično in je bil vedno večji od 80 %. Jakopič and Benedik Determination of 90Sr in Environmetal Samples