The silicon reacts with the ionic liquid and is irreversibly damaged during the

The silicon reacts with the ionic liquid and is

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electrodes. The silicon reacts with the ionic liquid and is irreversibly damaged during the course of an eNMR experiment. There are at least two other options available, both of which have been evaluated. One alternative is to melt the ends of the capillaries and allow the glass to seal the electrode in. An issue with doing this is that palladium expands when heated and once it cools off the seal is no longer tight, resulting in leaks and contamination of future samples. If a low enough temperature were to be used this problem should be negligible; this has thus far been difficult to achieve in practice and some small leakage is generally always found with melted electrodes. The second alternative investigated was to use non-sealed electrode capillaries. The major concern with using open capillaries is the capillary rise of the sample and its af- fect on the NMR spectrum. By weighing a sample before of water, inserting electrodes into the sample and weighing the remaining water after removing the electrodes a sam- ple/capillary volume ratio of 30 was found and the effect have subsequently been ignored. Using open capillaries is more time consuming than using sealed capillaries as they re- quire thorough cleaning and drying between each experiment. Open capillaries however show the most reproducible results and, as long as they are cleaned thoroughly between each experiment, showed no cross-sample contamination which was the main concern with melted glass capillaries. Once the eNMR cell was built, the exact distance between the resulting two electrodes needed to be established. As previously described by Hallberg et al. [ 4 ], this was done by running eNMR experiments on 10 mM sample solutions with known electrophoretic mobility, in this case that of Tetramethylammonium Bromide, TMA Br. Three exper- iments were made on different samples of the same concentration and the difference in electrophoretic mobility from the eNMR experiment and literature data gives a length calibration factor that was used to normalize all eNMR results obtained with the eNMR cell. For the electrodes used in the measurements presented in this report, the length calibration provided an effective electrode-electrode distance of 40.0 mm.
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18 CHAPTER 2. SUMMARY OF RESEARCH 2.2 Problems encountered A significant amount of project time has been devoted to investigating different solutions to the problems that might occur when running eNMR experiments on ionic liquids. The difficulties lie with the low diffusion coefficient for ionic liquids, their relatively high conductivity and finding a non-charged reference for phasing. In the process of developing a method for determination of the degree of dissociation of an ionic liquid these problems have been addressed. The high conductivity of ionic liquids compared to the samples routinely investigated by eNMR presents a significant problem with Joule heating. Two significant problems can occur, the first is the introduction of convection in the sample due to temperature
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