NMR relaxation studies of multicomponent emulsion systems
Nuclear magnetic resonance relaxation studies of multicomponent systems and fat tissues have been carried out on a home built spectrometer operating at 2.5 MHz. Throughout the entire work, the IR and CPMG pulse sequences were respectively utilised for the spin-lattice and spin-spin relaxation measurements. In IR experiments, the signals were collected at either equally or exponentially spaced time intervals depending on the average relaxation time T1 of the sample. In CPMG experiments, data were collected and averaged at 100 point intervals. An automatic temperature control unit has been constructed to monitor and maitain the sample temperature. In the present work, the temperature was held at 24.5 °C unless otherwise stated. The unit, which consists of an amplifier, a heating coil and a copper-constantan thermocouple, is linear and fast in response to the ambient temperature change with a sensitivity of 10.2 mV/ C. The unit does not introduce any interference on the NMR signal. Factors affecting the accuracy and the resolution of a two- component system have been investigated using two copper sulphate solutions contained in two concentric tubes. A curve-fitting procedure was used to determine the relaxation parameters. It is found that each component must be at least 10 % of the total in order to be detected. The ratio of the time constants also influences the accuracy and the resolution of the decay curves. Emulsions were prepared using n-hexadecane/water, paraffin oil/water and olive oil/water systems. Analysing the data according to one- and two-exponential models reveals that n- hexadecane and paraffin oil emulsions behave more like a two- component non-exchange system. Olive oil emulsion however appears to be more complex than expected. The complexity is attributable to the existence of at least three populations of spins. Studies with fat tissues indicate that the relaxation times may differ from species to species. In a particular species, however, the times appear to be constant irrespective of the region from where the tissues are extracted. Studies also reveal that water alone cannot account for the non-linearity of the decay curve. Relaxation behaviour of the olive oil emulsion differs somewhat from that of the fat tissues. Suggestions to prepare an emulsion having similar relaxation properties are discussed.