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Precise and accurate isotope ratio measurements are an important task in many applications such as isotope-dilution mass spectrometry, bioavailability studies, or the determination of isotope variations in geological or nuclear samples. The technique of MC-ICP-MS has attracted much attention because it permits the precise measurement of isotope compositions for a wide range of elements combined with excellent detection limits due to high ionisation efficiencies. However, the results are based mainly on measurements using continuous sample introduction. In the present study the determination of isotope ratios on various transient signals with a time duration of 30 to 60 s has been achieved by coupling high-performance liquid chromatography to a multicollector inductively coupled plasma mass spectrometer. In order to investigate the origin of ratio drifts across the transient signals for this hyphenated technique, measurements with the same standard solutions were also carried out using a flow-injection device for sample introduction. As a result of this application it could be concluded that the main source of the bias in the measured isotope ratios is within the ICP-MS instead of fractionation effects on the chromatographic column material. Preliminary studies on short transient signals of gaseous samples (dry plasma) showed a reverse fractionation effect compared with wet plasma conditions (flow injection and HPLC).

The influence of the radiolytic degradation products of bitumen on the speciation of radionuclides was studied under conditions which reflect those in the near field of a cementitious rad waste repository. The potential complexation capacity of the degradation products was studied and complexation experiments with Cu 2+ , Ni 2+ and UO| + were performed. In general 1:1 complexes with log Κ values of between 5.7 and 6.0 for Cu 2+ , 4.2 for Ni 2+ and 6.1 for UC>2 + were produced at an ionic strength of μ=0.1. The values are in good agreement with those found in the literature for oxalate complexes and suggest that oxalate determines the speciation of Cu 2 + , Ni 2+ and U0 2 + in the bitumen water at pH<7. However, under the high pH conditions typical of the near field of a cementitious repository, competition with OH-ligands will be large and oxalate, therefore, will not play a significant role in the speciation of radionuclides. The main conclusion of the study is that the degradation products of bitumen will have no influence on radionuclide speciation in a cementitious near-field and, as such, should not be considered in appropriate safety assessment models.

The adsorption of "Sr^"^ on bitumen emulsions with well characterized surfaces was studied as Function of pH and ionic strength of the equilibrium Solution. The bitumen/solution Interface is negatively charged due to the deprotonation of weakly acidic carboxyl groups present at the surface. The surface group density is calculated to be 1.37 • 10'® groups/m^ and the deprotonation behaviour can be fairly well desribed by the lonizable Surface Group Model with a pKH=6.6.Sr^'^ adsorbs on the bitumen by an outer sphere complexation reaction in which one surface carboxyl group is involved in the adsorption of one Sr^'^-ion. The adsorption depends on the ionic strength and pH of the contact Solution. The higher the ionic strength, the lower the adsorption. Sorption increases with increasing pH due to the deprotonation of carboxyl groups.In a cementitious environment, Sr^ adsorption on bitumen is negUgible due to the strong competition of Na , K and Ca^ present in the cement pore water. NaOH (pH = 11) were added and the mixture heated to 80-90°C and then stirred vigorously at 24000 rpm for 5 minutes by a high speed mixer (Ultra-Turrax, T-25; Janke and Kunkel, IKA). After cooling to room temperature, the emulsion was poured in an Erlenmeyer flask and left Standing overnight.A 50 ml aliquot of the emulsion was placed in a dialysis bag (Dialysis Tubing-Visking, Medicell London) and equilibrated with 10"^ M NaOH containing different NaC104 concentrations. The solutions were replaced 4 times at intervals of about 2 hours. After the fourth replacement, the conditioned bitumen emulsion was filtered through a 40 um nominal pore size nylon membrane (Nytal, nylon monofilament). The filtered Solution was used for adsorption experiments, dry weight determination, particle size analysis and surface group density measurements.