Research Report on Development of analytical strategies to measure radioisotopes of tin in the environment Prepared by Mohammad Majibur Rahman Graduate Program (PhD) Supervisor: Dr. Ian Clark Co-supervisor: Dr. Liam Kieser Earth and Environmental Sciences: Specialization in Chemical and Environmental Toxicology Submitted to The Office of Graduate and Postdoctoral Studies Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth and Environmental Sciences: Specialization in Chemical and Environmental Toxicology DECEMBER 13, 2018 © Mohammad Majibur Rahman, Ottawa, Canada, 2018 This page has intentionally been left blank. Abstract Quantification of tin isotopes in environmental samples, particularly the radioactive 126Sn, is important for processes such as the biomonitoring of organotin species, long-term nuclear waste storage and treatment planning. The detection of 126Sn by mass spectrometric methods is, however, hampered by the presence of the stable 126Te isotope. Therefore, separation of tin from tellurium is crucial to minimize isobaric interferences that limit the quantification of 126Sn by Accelerator Mass Spectrometry (AMS) and other instrumental techniques. In the present study, three major accomplishments are discussed: i) development of an analytical strategy to separate tin from tellurium, ii) monitoring of anionic interferences in the separation of tin from tellurium, and iii) suppression of 126Te background to allow the detection of 126Sn by AMS. Section I (Chapter 2): In the first phase of the project, an analytical survey was carried out using four Eichrom resins (TRU, TEVA, UTEVA, and DGA) to identify a suitable solid phase chromatographic material to separate tin from tellurium. Standard metal solutions were spiked on batch tests in two acids (HCl and HNO3) at concentrations ranging from 0.20 to 6.0 mol L–1, and the spiked analytes in solution were measured by ICP-MS. The distribution coefficient, KD (solid phase/aqueous phase) of tin and tellurium was then calculated for each resin. Results, HCl treatment from 0.20 to 6.0 mol L–1, reveal that the -1 TEVA resin exhibited the highest KD (27198 mL g ) for the tin in HCl solution, followed by TRU (24239 mL g-1), DGA (10165 mL g-1), and UTEVA (3232 mL g-1) -1 resins. However, the TRU resin demonstrated the lowest KD (431 mL g ) for tellurium in similar acid conditions compared to other substrates (UTEVA 708 mL g-1, DGA 2230 mL -1 -1 g , and TEVA 3124 mL g ). All four resins produced relatively small KD values (≤ 100 -1 mL g ) for both tin and tellurium in aqueous HNO3 medium. A follow up of batch test, in ii which the TRU resin was charged on Bio-Rad columns, showed retention of 99.78 ± 0.39% tin and 59.31 ± 1.30% tellurium in the presence of dilute hydrochloric acid (~1.0 mol L–1). Through a study of tin and tellurium desorption from TRU resin with different eluents, it was observed that aqueous hydrofluoric acid (~ 0.50 mol L–1) could wash down up to 92% of loaded tin, while tellurium desorption can be kept as low as 5%. The first phase of our work suggests that the TRU resin offers itself a promising solid phase chromatographic material for the separation of tin from tellurium, while aqueous hydrofluoric acid is shown to be an excellent eluent to selectively wash out of tin from the solid phase. Section II (Chapter 3): In the second phase of the project, experimental work was carried out to evaluate the – 2– effect of Cl and SO4 interferences, the two major anions found in natural waters, in the separation of tin from tellurium. Following previous findings, powdered TRU (50–100 μm) resin was used as an adsorbent. Laboratory prepared solutions containing Cl– and 2– – 2– – 2– SO4 ions were spiked (single Cl , single SO4 , and Cl -SO4 -mixed spike) with standard solutions of tin and tellurium. Distribution coefficients for adsorbed tin and tellurium were then determined for each solution. An optimization of the reaction time producing the maximum metal-resin interaction was also evaluated. –1 Results reveal that the average KD values for tin and tellurium in 3.0 mol L hydrochloric acid are 5517 ± 406 and 1310 ± 50 mL g–1, respectively. In the case of tin, the Cl–-spike produced an increase in KD of 11% from that of the unspiked sample, whereas the mixed- spiked sample faced a reduction of KD by 7% compared to that of the unspiked sample. The distribution coefficients of tellurium in the presence of tested anion spikes remained unchanged. This observation demonstrates that the distribution coefficients of tin and – 2– tellurium onto the solid phase is barely affected by the presence of Cl and SO4 iii contaminants (each present at concentrations of 70.0 mg L–1). Moreover, the adsorption – 2– of metal at very low acidic conditions onto the resin in presence of Cl and SO4 spikes is favored at pH values from 4.0 to 5.0. In alkaline conditions, the resin was found to lose its stability. The TRU resin undergoes denaturation at 2.0 mol L–1 of NaOH, while a complete annihilation of resin structure occurred at 3.5 mol L–1 of base. The optimization of the reaction time producing the highest distribution coefficient of metals on the solid phase was carried out by observing batch tests up to 180 minutes of contact time. Results show that the optimum time for the best metal-resin interaction is around 90 minutes. More prolonged interaction time reduce the KD values for both tin and tellurium. A thorough adsorption-desorption study for tin and tellurium using TRU chromatographic resin with spiked field samples (surface and groundwaters) show that at least 99% tin is adsorbed in the presence of hydrochloric acid, while the adsorption of tellurium can be maintained at a level as low as 60%. Aqueous hydrofluoric acid can then selectively elute 85% of tin (with a single wash of 100 mg of TRU resin) with tellurium release of less than 10%. Our proposed methodology can be applied successfully for the selective separation of tin from tellurium from surface and groundwater samples containing Cl– 2– and SO4 ions. iv Section III (Chapter 4): In the third phase of our project, a rigorous study was carried out to suppress the 126Te background for the detection of 126Sn by AMS. Laboratory prepared and commercially available SnF2 along with SnI2 were used in the preparation of AMS targets (SnF2 + PbF2 – – and SnF2 + NaI + Ag). Beam-currents for SnF5 and SnF2I molecular ions were measured from these targets in the A. E. Lalonde AMS laboratory. Results reveal that: - tin does not form a stable molecular-beam with iodine, iodine makes the ion- source very unstable, no beam-current was detected with iodide species, even after mixing with silver powder, – - the formation of large SnI2F molecular ion was not confirmed, no detectable signal was observed for this compound, – – - no stable beam-current was observed for TeF3 and TeF5 species, – - the molecule SnF2 is a good ionic conductor, which produces stable SnF3 current, - the sputtering capacity of SnF2 is very good and immediate, and SnF2 + PbF2 – target composition yields a long-lasting SnF3 current, 126 120 - the Sn/ Sn ratio with laboratory prepared SnF2 was measured as ~4.0 × 10–9, a suppression of tellurium background to ppb-level, 126 118 –11 - the Sn/ Sn ratio with the SnF2 compound was found to be ~7.0 × 10 , a drop of background by 2-orders of magnitude, 126 118 - the Sn/ Sn ratio for the commercial SnF2 sample was measured as ~3.0 × 10–12, a drop of background to parts per trillion-level. The observed ~10–12 background is the lowest value ever measured for the AMS quantification of 126Sn, even large AMS techniques have not reported lower 126Sn/118Sn ratios. Therefore, the SnF2 + PbF2 target composition is an excellent choice to produce v stable molecular ion beams of tin and reducing interferences caused by the presence of 126Te isotope during the detection of 126Sn by AMS. Keywords Tin isotopes, distribution coefficient, solid phase extraction, extraction chromatographic materials, TRU resin, metal adsorption-desorption, ICP-MS, anionic interferences on distribution coefficient, groundwater contamination, AMS detection of 126Sn, 126Te interference, suppression of 126Te background, AMS beam-current. vi Statement of originality This is to certify that the content of this thesis is done by me and has not been submitted elsewhere for any academic degree or diploma. I also testify that this booklet is independently prepared by me and the assistances received from other sources have been acknowledged or cited as references. The chapter 4 (AMS detection of 126Sn) has been developed with the generous cooperation of Dr. Xiaolei Zhao, A. E. Lalonde AMS Laboratory, Advanced Research Complex, University of Ottawa. I am indebted to him for his time- consuming help in the analysis of AMS data. © Mohammad Majibur Rahman vii Acknowledgements I would like to express my deepest sense of gratitude to Prof. Ian Clark and Prof. Liam Kieser, for their kind consent to accept me as a graduate student after the sudden demise of Prof. Robert Jack Cornett. I can recall those critical days when a vibrant research group was facing a serious mentoring problem, fortunately, Ian and Liam came forward and took the burden on their shoulders. The strong moral support, caring guidance, and constant encouragement I have received from them, were amazing. In fact, without their escalating push, I could hardly have finished the time-sensitive project work well before the anticipated deadline. My thankful acknowledgement goes to them. I am grateful to Dr. Nimal De Silva, Smitarani Mohanty, and Cole MacDonald for their extended cooperation in instrumental troubleshooting during the ICP-MS sample run.