Chromatography anomalies

Hydrocarbon Anomalies in Soils Soil samples were collected at 200 to 500 m intervals over the Lisbon and Lightning Draw fields and analyzed for thermally desorbed Ci to C12 alkanes by Flame Ionization Detection Gas Chromatography (GC-FID) and solvent-extractable Ce to C36 aromatics by UV-fluorescence spectrophotometry. 

Despite that chromatography is a relatively exact method, it has some drawbacks such as the presence of anomalies, just like any known analytical method. The anomalies that arise from chromatography are very difficult to classify. However, an attempt will be made in the following discussion to highlight the main types of anomalies in chromatographic analysis. 

Fig. 8-9. Solvent strength and the ether anomaly in dilute solutions of ethyl ether in pentane. Adsorption on 3.8% H2O-AI..O3. Reprinted from the Journal of Chromatography 12) by permission of Elsevier Publishing Company.

The coefficient of sell-diffusion does not appear to have an anomaly near the critical point. For the engineer, however, the mutual dift usion coefficient is the more important property. The binary dilfusion coefficient approaches zero at the mixture critical point ("critical slowing-down"). In dilute mixtures, however, the decrease of the binary dilfusion coefficient is not seen until the critical line is approached very closely. For many practical purposes, such as supercritical extraction and chromatography, the mixture is dilute, and it can be assumed that the coefficient of binary diffusion is intermediate between that in the vapor and that in the liquid. Since the diffusion coefficient decreases roughly inversely proportional to the density, dilfusion in supercritical solvents is much more rapid than in liquid solvents, thus increasing the speed of diffusion-controlled chemical processes. 

A few reports are available where TIMS has been used for cosmochemical analysis. The recent report of Yamakawa et al. (2009) deals with sequential chemical separation technique for Cr, Fe, Ni, Zn, and Cu in terrestrial and extraterrestrial silicate rocks for precise and accurate determination of elemental concentration. The chemical technique uses a combination of cation-anion exchange chromatography and Eichrom nickel specific resin. The developed method was tested to a variety of matrixes bulk meteorite (Allende), terrestrial peridotite (JP-1), and basalt (JB-lb). Concentrations of each element were determined by TIMS. The analytical procedure was further extended to obtain high-precision isotope data for Cr. The method is capable to determine the isotopic ratios of Cr/ Cr and Cr/ Cr with precision of 5 X 10 and 1 x 10, respectively. The method can be equally applicable in cosmochemical studies, like Mn-Cr chronology and investigation of nucleosynthetic isotopic anomalies in meteorites. The elemental concentrations measured by TIMS in Allende are, for example, Cr 3,600 0.007 ppm, Fe 233,400 0.009 ppm, Ni 14,020 0.006 ppm, Cu 107 0.013 ppm, and Zn 117.8 0.01 ppm. The detection of Al (0.7 Ma) in the Allende meteorite proves that nucleosynthesis is still active in the Milky Way as the half-life of A1 is much less than the timescale of galactic evolution (10 years). 

In order to clear up these anomalies the progress of the polymerization in dichloroethane with boron-trifluoride at different temperatures was investigated. Hereto the decrease of the monomer has been determined by gas chromatography (39). An example of a time-conversion curve is shown in Fig.3. The polymerization proceeds rather quickly the monomer concentration reaches a final state, which does not change over several hours. This concentration increases with increasing polymerization temperature (see Table 2). These facts lead us to conclude that it is an equilibrium polymerization. The plot of In (M) against 1/T for temperatures between QO and 60°C is shown in Fig.4. We calculated A Sss -18,9 J/Mol K and -aHss = -6,6 kJ/Mol. By extrapolation to a monomer concentration of (M) 1 Mol/1 in equilibrium, a formal ceiling temperature of 80°C results. In fact at 80°C and with a monomer concentration of 1 Mol/1 no polymerization takes place. 

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