Polynuclear aromatic hydrocarbon materials

Silica gel, per se, is not so frequently used in LC as the reversed phases or the bonded phases, because silica separates substances largely by polar interactions with the silanol groups on the silica surface. In contrast, the reversed and bonded phases separate material largely by interactions with the dispersive components of the solute. As the dispersive character of substances, in general, vary more subtly than does their polar character, the reversed and bonded phases are usually preferred. In addition, silica has a significant solubility in many solvents, particularly aqueous solvents and, thus, silica columns can be less stable than those packed with bonded phases. The analytical procedure can be a little more complex and costly with silica gel columns as, in general, a wider variety of more expensive solvents are required. Reversed and bonded phases utilize blended solvents such as hexane/ethanol, methanol/water or acetonitrile/water mixtures as the mobile phase and, consequently, are considerably more economical. Nevertheless, silica gel has certain areas of application for which it is particularly useful and is very effective for separating polarizable substances such as the polynuclear aromatic hydrocarbons and substances... 

Standardization. Standardization in analytical chemistry, in which standards are used to relate the instrument signal to compound concentration, is the critical function for determining the relative concentrations of species In a wide variety of matrices. Environmental Standard Reference Materials (SRM s) have been developed for various polynuclear aromatic hydrocarbons (PAH s). Information on SRM s can be obtained from the Office of Standard Reference Materials, National Bureau of Standards, Gaithersburg, MD 20899. Summarized in Table VII, these SRM s range from "pure compounds" in aqueous and organic solvents to "natural" matrices such as shale oil and urban and diesel particulate materials. 

May, W.E., Brown, J.M., Chester, S.N., Guenther, F., Hilpert, L.R., Hertz, H.S., Wise, S.A. (1979) Development of an aqueous polynuclear aromatic hydrocarbon standard reference material. In Polynuclear Aromatic Hydrocarbons. Jones, P.W., Leber, P., Editors, pp. 411-418, Ann Arbor Science Publishers, Inc., Ann Arbor, Michigan. 

Shigenaka, G. and Henry, C.B. Jr. 1995, Use of Mussels and Semipermeable Membrane Devices To Assess Bioavailability of Residual Polynuclear Aromatic Hydrocarbons Three Years After the Exxon Valdez Oil Spill. In Exxon Valdez Oil Spill Fate and Effects in Alaskan Waters Wells, P.G., Butler, J.N., Hughes, J.S, Eds. American Society for Testing and Materials Philadelphia, PA. pp. 239-260. 

After a plate has been exposed to the mobile-phase solvent for the required time, the compounds present can be viewed by several methods. Polynuclear aromatic hydrocarbons, other compounds with conjugated systems, and compounds containing heteroatoms (nitrogen, oxygen, or sulfur) can be viewed with long-and short-wave ultraviolet light. The unaided eye can see other material, or the plates can be developed in iodine. Iodine has an affinity for most petroleum compounds, including the saturated hydrocarbons, and stains the compounds a reddish-brown color. 

Wershaw RL (1986) A new model for humic materials and their interactions with hydrophobic organic chemicals in soil-water or in sediment-water systems. J Contam Hydrol 1 29-45 Whitehouse BG (1984) The effect of temperature and salinity on the aqueous solubility of polynuclear aromatic hydrocarbons. Mar Chem 14 319-332 Wolters A, Linnemann V, Herbst M, Klein M, Schaffer A, Vereecken H (2003) Pesticide volatihzation from soil Lysimeter measurements versus predictions of European registration models. J Environ Qual 32 1183-1193... 

According to the developer, the TDU removes volatile organic compounds and volatile metals from soil. The technology is designed to treat material contaminated with polychlorinated biphenyls (RGBs), polynuclear aromatic hydrocarbons (PAHs), dioxins, and volatile heavy metals (mercury). 

The identifiable compounds in coke-oven and petroleum pitches are mainly polynuclear aromatic hydrocarbons. Proton magnetic resonance spectra of solvent-soluble fractions of these materials show that over 90 of the protons are attached to aromatic rings. Under the conditions of carbonization it would... 

In this paper, the supercritical fluid extraction (SFE) of organic compounds from sand spiked with 36 nitroaromatic compounds, 19 haloethers, and 42 organochlorine pesticides, and from a standard reference material certified for 13 polynuclear aromatic hydrocarbons (PAH), dibenzofuran, and pentachlorophenol was examined using a two- and a four-vessel extractor. Although the results achieved by SFE for the sand and the standard reference soil samples were very encouraging, previous data obtained in our laboratory on the standard reference soil and a few other standard reference marine sediments were less favorable. It was therefore decided that an investigation of seven variables for their influence on the analyte recoveries from the standard soil sample would be useful. Two tests were conducted in which these variables were investigated. In Test 1, the seven variables selected were pressure, temperature, moisture content, cell volume, sample size, extraction time, and modifier volume. In Test 2, the seven variables were pressure, temperature, volume of toluene added to the matrix, volume of solvent in the collection vessel,... 

Although the great majority of petroleum and coal-based pitch materials, as well as model compounds such as polyvinyl chloride, acenaphthylene, decacyclene and polynuclear aromatic hydrocarbons, form anisotropic graphitizable carbons, it is an almost impossible task to predict the type of optical texture of a coke from an elemental analysis of the pitch. The size, shape and reactivity of peri-condensed polynuclear aromatic molecules in the products of pyrolysis of a pitch play a more important role in determining optical texture. 

The black material in diesel exhaust consists of small particles that are rich in polynuclear aromatic hydrocarbons. 

When the heating is prolonged or carried out at higher temperatures, polynuclear aromatic hydrocarbons with up to 7 rings form (Fig. 4 Studier et al., 1965a, 1968 Oro and Han, 1966 Friedman et al, 1970). This reaction, using CH as the starting material, was discovered by Berthelot over a century ago. 

It may be taken on the basis of these results that modern combustion calorimetry can obtain results which are usually reproducible from laboratory to laboratory to within 0 02-0-05 per cent. To obtain this precision it is necessary to have the substances concerned very pure it is probable that differences between the results of different authors are due rather to differences in purity of the samples than to defects of calorimetric technique. This is illustrated by the results given in Table 7,L3 for some polynuclear aromatic hydrocarbons, where the agreement is much less satisfactory, presumably for this reason. Bender and Farber 2 attribute their high results to superior purity of sample, and point out that the most carefully purified materials used in previous work were those of Fries et with whom they are nearly in agreement. Magnus... 

Figure 2. Separation scheme for polynuclear aromatic hydrocarbon subfractions from fossil-derived materials...

Polynuclear Aromatic Hydrocarbons in Environmental Materials Extract Supercritical Fluid Extraction... 

As discussed in previous sections, there are numerous factors that can modify the toxicity of materials. The prediction of the toxicity of mixtures is also difficult. One of the best attempts at toxicity prediction has been formulated by Swartz et al. (1995) and predicts the sediment toxicity of polynuclear aromatic hydrocarbons. The model is based on the concentration of 13 PAHs in collected sediments, the predicted concentration in the sediment pore water, and the toxicity of these concentrations as determined by a large toxicity data set. 

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