Hydrogen isotope type-curves of very hot crude oils

Several crude oil accumulations in the Pannonian Basin are trapped in uncommonly hot (>170°C) reservoirs. Their maturities range from mature to very mature on the basis of cracking parameters of their biological marker homologous series (ratio of products to reactants). A stable carbon isotopic study of these oils, poor in biological markers commonly used for correlation purposes, did not provide a reliable oil-to-oil correlation. As an alternative tool, the hydrogen isotope compositions of oil fractions separated on the basis of different polarities were measured, and hydrogen isotope type-curves were generated for a set of mature to very mature crude oil samples. This method of presenting hydrogen isotope composition of fractions as type-curves is novel. Nineteen samples (17 crude oils from SE-Hungary, 1 oil condensate and 1 artificial oil) were chosen for the present study. The aim was to examine the applicability of hydrogen isotope type-curves in oil-to-oil correlation and to test the simultaneous application of carbon and hydrogen isotope type-curves in the field of petroleum geochemistry. We have shown that, although the conventionally used co-variation plots proved to be inadequate for the correlation of these hot and mature oils, the simultaneous use of carbon and the newly introduced hydrogen isotope type-curves allows us to group and distinguish oils of different origins.     

Composition depth profile analysis of electrodeposited alloys and metal multilayers: the reverse approach

The reverse depth profile analysis is a recently developed method for the study of a deposit composition profile in the near-substrate zone. The sample preparation technique enables one to separate the deposit and a thin cover layer from its substrate, and the initial roughness of the sample is much smaller than in the conventional sputtering direction. This technique is particularly suitable to study the zones being formed in the early phase of the electrodeposition of alloys. It has been demonstrated with the reverse depth profile analysis that in many cases when one component of an alloy is preferentially deposited, an initial zone is formed that is rich in the preferentially deposited component. This phenomenon is demonstrated for Ni–Cd, Ni–Sn, Fe–Co–Ni, Co–Ni, and Co–Ni–Cu alloys. The composition change is confined to the initial 150-nm-thick deposit, and it is the result of the interplay of the deposition preference and the depletion of the electrolyte near the cathode with respect to the ion reduced preferentially. The reverse depth profile analysis made it possible to compare the measured and the calculated composition depth profile of electrodeposited multilayers. It has been shown that the decay in the composition oscillation intensity in Co/Cu multilayers with the increase of the sputtering depth can be derived from the roughness measured as a function of the deposit thickness.     

Method validation for the simultaneous determination of fecal sterols in surface waters by gas chromatography-mass spectrometry

Besides microbiological methods, fecal pollution of surface waters is estimated by gas chromatographic (GC) determination of sterols present in human and animal sewage effluents. The most frequently used biomarkers for the evaluation of contamination levels include coprostanol, cholesterol, dihydrocholesterol, stigmasterol, beta-sitosterol, and stigmastanol. Although several GC techniques are used to measure these compounds in aquatic systems, the analytical performance of GC-mass spectrometric (MS) determination of these sterols has not been systematically characterized. Therefore, the aim of this work is to validate a simple and rapid GC-MS method for the simultaneous analysis of six sterols, considering all parameters and requirements defined by Good Laboratory Practice. Following liquid-liquid extraction of spiked surface water samples, the extracts are silylated and analyzed by GC-MS. The method is evaluated for linearity and limits of detection and quantitation, as well as for precision, extraction efficiency, and stability. The assay is linear up to 160 ng; the limits of detection and quantitation are 5-10 ng and 20 ng, respectively. The within- and between-day precision ranged from 1% to 9% and 1% to 16%, respectively. The extraction efficiency was 65-80%. The stability studies indicate that the sterols in surface water samples begin to degrade after 24 h of refrigerated storage. However, three freeze/thaw cycles could be performed without their decomposition. The method is applied to the analysis of surface water and wastewater samples. The technical advantages make this GC-MS analysis suitable for routine environmental monitoring of fecal pollution in aquatic systems.     

Kinetics and mechanism of the oxidation of sulfite by chlorine dioxide in a slightly acidic medium

The sulfite-chlorine dioxide reaction was studied by stopped-flow method at I = 0.5 M and at 25.0 +/- 0.1 degrees C in a slightly acidic medium. The stoichiometry was found to be 2 SO(3)(2-) + 2.ClO(2) + H(2)O --> 2SO(4)(2) (-) + Cl(-) + ClO(3)(-) + 2H(+) in *ClO(2) excess and 6SO(3)(2-) + 2*ClO(2) --> S(2)O(6)(2-) + 4SO(4)(2-) + 2Cl(-) in total sulfite excess ([S(IV)] = [H(2)SO(3)] + [HSO(3)(-)] + [SO(3)(2-)]). A nine-step model with four fitted kinetic parameters is suggested in which the proposed adduct *SO(3)ClO(2)(2-) plays a significant role. The pH-dependence of the kinetic traces indicates that SO(3)(2-) reacts much faster with *ClO(2) than HSO(3)(-) does.     

A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: the importance of inverse trans influence.

During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (T(c)), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions.