The distribution of NMR relaxation times and diffusion coefficients has been employed for modeling the composition of typical crude oils both in bulk and in the reservoir rock. Although the relation of relaxation times and diffusion coefficients with viscosity and molecular size in a typical maltene composition has been established for bulk oils, it is known that the presence of asphaltene affects the relaxation times in a complex way not sufficiently understood so far. In particular, it is expected that the interaction of aromatic or aliphatic maltene molecules, respectively, with asphaltene aggregates leads to a different influence on the relaxation time. In this study, we have applied, for the first time, fluorine containing tracer molecules to natural oils of different asphaltene content and investigated the tracers’ relaxation time ratios T 1/T 2 and the magnetic field dependence of longitudinal relaxation times, T 1(ω). This strategy has the advantage of specifically determining the behavior of individual tracer molecules, where molecular weight and aromaticity have been considered as variables. One main finding of this study is the remarkably strong change of T 1/T 2 between perfluorinated alkanes and aromatics in the presence of asphaltenes, whereas this ratio remains nearly constant for asphaltene-free oils. The results are interpreted in terms of selective maltene–asphaltene interaction on the basis of frequency dependent relaxation results. The strong contrast of relaxation times allows for a simplified quantification of either asphaltene concentration or aromaticity of maltenes in natural oils.

The broad distribution of NMR proton relaxation times in crude oil is a consequence not only of the overlap of a multitude of different constituents, but also of interactions of different strength with asphaltene aggregates, which was found to be influenced by the maltenes’ aromaticity. The so-called dispersion, or frequency dependence, of the longitudinal relaxation time T 1(ω), and the ratio T 1/T 2 as a related parameter, becomes more pronounced for aromatic solvent molecules, in particular for fluorine-containing tracers, and is assumed to be a consequence of either or both the nuclear-electron interaction with the asphaltenes’ radical component or geometric trapping of maltenes within the asphaltene aggregates in crude oil. In this work, we seek proof for this assumption by investigating the concentration dependence of relaxation properties in solutions of asphaltenes, and by comparing the relaxation properties to a number of simplified model solutions possessing either similar geometry or radical concentration. The notion of an enhanced interaction strength is further supported by dynamic nuclear polarization experiments of native crude oil doped with selected tracer molecules.

A new detection technique called the fast Fourier transform square-wave voltammetry (FFT SWV) is based on measurements of electrode admittance as a function of potential. The response of the detector (microelectrode) is fast, which makes the method suitable for most applications involving flowing electrolytes. The carbon paste electrode was modified by nanostructures to improve better sensivity. The redox property of Diphenhydramin was used for determination of it in human serum and urine samples. Synthesized dysprosium nanowires make more effective surface like nanotubes [1-4] so they are good candidates for using as a modifier for electrochemical reactions. The drug presented one irreversible oxidation peaks at 1080mV vs. Ag/ AgCl by modified Nanowire carbon paste electrode which produced high current and reduced the oxidation potential about 300mV. Furthermore, signalto-noise ratio has significantly increased by application of discrete fast Fourier Transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. To obtain the much sensivity the effective parameters such as frequency, amplitude and pH was optimized. As a result, LOD of 4.0 ×10-11 mol l -1 and an LOQ of 8.0× 10 -11 mol l -1 were found for determination for Diphenhydramin. A good recovery was obtained for assay spiked urine samples and a good quantification of Diphenhydramin was achieved in a commercial formulation.

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