Function Of Organic Content Research Articles

Probing selectivity of mixed-mode reversed-phase/weak-anion-exchange liquid chromatography to advance method development

The current study comprises a systematic investigation to assess retention properties and selectivity of a mixed-mode reversed-phase/weak-anion-exchange (RP/WAX) stationary phase to aid method development. Retention was investigated for different compound classes which vary in hydrophobicity, van der Waals surface area, and charge as function of organic content, pH, and ionic strength of the mobile phase. The linear-solvent-strength model was successfully applied for aromatic hydrocarbons to obtain retention-time predictions based on log P values and van der Waals surface area values. For phenols, predictions were based on log P values and data from a single scouting run performed in isocratic mode to estimate the S parameter; the deviations between experimental and predicted retention times were smaller than 6%. To describe the mixed-mode (RP/WAX) retention behavior of singly and doubly negatively-charged aromatic acids, a novel model combining the linear-solvent-strength and the empirical stoichiometric-displacement-net-charge models is proposed and validated. Using combinations of three scouting runs that are not linearly dependent, the maximum prediction error was 11% and changes in selectivity were correctly forecasted when altering the mobile-phase composition, i.e., either organic modifier content or ionic strength. When using nine scouting runs in combination with a least-squares regression approach to determine the model parameters, the maximum prediction error was 6%.

Evaluation of opto-mechanical properties of UV-cured and thermally-cured sol-gel hybrids monoliths as a function of organic content and curing process

We fabricated sol-gel monoliths using a fast sol-gel (FSG) technique with either UV-curing or thermal-curing, producing highly dense, stable monoliths in a short time. This paper focuses on the preparation and the characterization of different FSG compositions as a function of the inorganic-organic molar-ratio and curing-mechanism. The fabrication of the monoliths was based on three precursors, tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), and methacryloxypropyl-trimethoxysilane (MAPTMS). Three series of FSG monoliths with different material compositions were synthesized. The organic content in the final monoliths varied from 17 to 52weightpercent (wt%). We established the range of precursor's molar-ratios that permit formation of stable low-organic content optical monoliths by UV-curing. The physical properties of the monoliths formed under different curing conditions were examined. The refractive-index increased with increased thermal-curing temperature and for combined thermal and UV-curing. On the other hand, the coefficient of thermal expansion (CTE) increases with the organic content for thermally-cured samples and decreases for UV-cured samples, due to full crosslinking. Additional important physical properties for sol-gel applications such as weight-loss, porosity and adhesive strength are also presented. The results obtained give guidelines for fabricating useful optical monoliths with lower CTE using a UV-curing process for applications such as optical bonding and encapsulation.

From optics to upscaled thermal conductivity: Green River oil shale

A novel approach for high-resolution (∼1cm) spatial mapping of thermal conductivity from optical photographs of oil shale is developed and applied to the Mahogany Zone of the Green River Formation. A theoretically consistent constitutive equation for conductivity, parallel/perpendicular to the geologic bedding, as a function of organic content and temperature is proposed for unretorted Green River oil shale and shown to be in agreement with all published experimental measurements to date. Conductivity maps of a core spanning the full thickness of the Mahogany Zone are numerically upscaled, for intervals 10–80cm long, and analytical equations capable of approximating the upscaled values to within ±5% error are presented. These obviate computationally costly numerical upscaling in the future. Upper bounds for upscaled anisotropy ratios (=parallel/perpendicular conductivity) were found to lie within 1.5 (typical case) and 2 (extreme case); with highest anisotropies occurring in the least conductive regions. The results of this work should benefit numerical models of in-situ retorting of oil shale resources at the core and field scales.

Interfacial Tensions of Aged Organic Aerosol Particle Mimics Using a Biphasic Microfluidic Platform.

Secondary organic aerosol (SOA) particles are a major component of atmospheric particulate matter, yet their formation processes and ambient properties are not well understood. These complex particles often contain multiple interfaces due to internal aqueous- and organic-phase partitioning. Aerosol interfaces can profoundly affect the fate of condensable organic compounds emitted into the atmosphere by altering the way in which ambient organic vapors interact with suspended particles. To accurately predict the evolution of SOA in the atmosphere, we must improve our understanding of aerosol interfaces. In this work, biphasic microscale flows are used to measure interfacial tension of reacting methylglyoxal, formaldehyde, and ammonium sulfate aqueous mixtures with a surrounding oil phase. Our experiments show a suppression of interfacial tension as a function of organic content that remains constant with reaction time for methylglyoxal-ammonium sulfate systems. We also reveal an unexpected time dependence of interfacial tension over a period of 48 h for ternary solutions of both methylglyoxal and formaldehyde in aqueous ammonium sulfate, indicating a more complicated behavior of surface activity where there is competition among dissolved organics. From these interfacial tension measurements, the morphology of aged atmospheric aerosols with internal liquid-liquid phase separation is inferred.

Two-dimensional liquid chromatography with mixed mode stationary phases

Mixed mode stationary phases with ion-pairing reagent (acidic or basic) as integral part of hydrophobic chain offers unique selectivity, and hence, are ideal for multidimensional separations. The retention of hydrophobic components is a function of organic content, whereas that of charged species is a function of organic content, ionogenic modifier and its level in the mobile phase. Hence, by controlling the parameters influencing component retention (stationary phase and mobile phase), the selectivity of chemical components in the two-dimensional plane can be manipulated to improve the separation. A two-dimensional liquid chromatograph has been developed by coupling similar and dissimilar mixed mode stationary phases in the two dimensions. This technique has immense potential in resolving co-eluting components as the retention mechanism in the two-dimensions are complementary. However, with only part of the primary column eluent sampled into the secondary column, the technique is limited to qualitative analysis.

Biogeochemistry of the MAximum TURbidity Zone of Estuaries (MATURE): some conclusions

In this paper, we give a short overview of the activities and main results of the MAximum TURbidity Zone of Estuaries (MATURE) project. Three estuaries (Elbe, Schelde and Gironde) have been sampled intensively during a joint 1-week campaign in both 1993 and 1994. We introduce the publicly available database, and compare trends and patterns in suspended matter, nutrients and organic matter in the three estuaries. Despite the large differences in suspended particulate matter concentrations between the estuaries, some general relationships can be deduced. Organic matter dynamics is shown to be determined by sorption onto the particulate matter. This in turn induces a predictable change in bacterial degradability. Floc size, determined by an in situ camera, is a function of organic content, suspended matter concentration and (in a highly non-linear way) salinity. Higher trophic levels in the biological system are negatively affected by the dilution of their food with indigestible particles.