Polyaromatic hydrocarbons reference materials

Carbon black is produced industrially in the form of different products (e.g., furnace black, thermal black, channel black, lampblack, acetylene black) with specific properties. In addition to the relevance of carbon black for basic research on adsorption, or as a reference sohd, appUcations of this material in fields such as elastomer reinforcement, as modifier of certain properties of plastics (UV protection, electrical conductance, color), or as xerographic toners make its surface and interfacial properties extremely important. Soot is a randomly formed particulate material similar in nature to carbon black. The main (pragmatic, rather than conceptual) difference between these two carbon forms is that soot is generally formed as an unwanted by-product of incomplete combustion of pyrolysis, whereas carbon black is produced under strictly controlled conditions. Bansal and Donnet [78] have reviewed various possible mechanisms for the formation of soot and carbon black. Soot can retain a number of tars and resins on its surface. There is therefore some interest in studying the adsorption of polyaromatic hydrocarbons in soots, especially those of environmental significance such as diesel soot. 

Determinations of polyaromatic hydrocarbons (PAHs) in freeze-dried sediments (sample mass of the order 10-20 g) has been carried out where hexa-methylbenzene added as a standard to the sediment prior to extraction. The sediments were extracted sequentially with methanol followed by methylene chloride and substituted and unsubstituted were determined by GC-MS. The accuracy of the method was verified using the marine reference material HS6 (NRCC). The technique allowed the determination of 17 unsubstituted and 33 substituted PAHs with detection limits in the range 50-200ngperg. An example of the results from the sediment core from a Canadian fjord contaminated with PAHs derived from an almnimun smelter is shown in Figure 3. The PAH concentration illustrates the wide concentration range available to this analytical method and also show the variation of PAH concentrations with depth. Each PAH has an increase in concentrations... 

Since in the simplified procedure only the hydrocarbon fraction from silica is reseparated on alumina, while in the extended procedure all the material remaining after removal of the saturates is rechromatographed on alumina, the contents of polyaromatics from the former is necessarily lower (9.4% ) than from the latter (28.6% ) procedure. The balance of material is represented in the simplified procedure by fraction Polar 1 (see also References 2, 3, and below). 

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