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Petroleum analysis presents many unique challenges as a result of the chemical complexity of petroleum composition. In the present work a novel chromatographic material has been developed and utilized to separate crude oils. A total number of 13 fractions have been collected using different solvent mixtures with increasing proportions of chloroform. UV and IR spectroscopy has been employed to show that the size of the aromatic ring system increases and the extent of molecular branching decreases with elution gradient. This observation suggests that intermolecular non-covalent π-π interactions between the material and the sample molecules are critical to the separation. This novel method for sequencing petroleum molecules based on the size of the aromatic ring systems has been applied to the 2D off-line analysis of crude oil samples. The 2D on-line separation (NPLC × NPLC) has been simulated by 2D off-line separation. A total number of 38 fractions have been obtained with two SPE columns based on the molecular branching and the aromatic ring system size. The chemical information obtained in this study of North Sea crude oil is complementary to standard SARA analysis. The material supports a potential solution to overcome the challenges of tandem NPLC and has demonstrated a new approach to the separation of crude oils into discrete compound classes.

A systematic study of the rotation constants, vibration–rotation constants and quartic centrifugal distortion constants has been performed for furan, pyrrole, thiophene, both oxazoles and thiazoles, 1,2,4- and 1,2,5-oxa- and -thiadiazoles, 1,2,5-selenadiazole, and several 6-membered heterocycles (azines). The main study used cc-pVTZ basis sets. There is a very close correlation between the observed constants above and those calculated, especially using the cc-pVTZ + B3LYP procedures; some trends in these appear on substitution of HC by N in the azoles. This strong correlation between experimental values and this theoretical procedure is also apparent with vibrational differences in rotation constants, all over large numbers of measured values. However, a small number of calculated values do not correlate well with experiment; this may be a result of some of the experimental values being subject to resonance perturbations not included in the calculations. In general, a TZ2P basis set with B3LYP methodology, and cc-pVTZ results with MP2 methodology, lead to correlations of similar quality, but the latter require markedly more computing power. The present study draws attention to a tetrad in the IR spectrum of 1,2,5-oxadiazole, where further analysis is necessary.

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500 2900 cm(-1) spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H-Cl stretching vibration band upsilon(2) of the linear HCN-(HCl)-Cl-35 heterodimer. The rovibrational analysis of the band yield a band origin upsilon(0) of 2779.0968(12) cm(-1) together with a value for the upper-state rotational constant B' of 0.067722(2) cm(-1). The observed red shift of 107 cm(-1) for the upsilon(2) band of HCN- (HCl)-Cl-35 relative to the H-Cl stretching vibration band of monomer (HCl)-Cl-35 is in excellent agreement with results from the MP2/ 6-311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Angstrom upon intramolecular vibrational excitation of the upsilon(2) mode. (C) 2004 Elsevier B.V. All rights reserved. (Less)