Extraction polyaromatic hydrocarbon from soil

Reindt and Hoffler [50] optimized parameters in the supercritical fluid extraction of polyaromatic hydrocarbons from soil. These workers used carbon dioxide -8% methanol for extraction and obtained 88-101% recovery of polyaromatic hydrocarbons in the final high-performance liquid chromatography. 

Barnabas et al. [51] have discussed an experimental design approach for the extraction of polyaromatic hydrocarbons from soil using supercritical carbon dioxide. They studied 16 different polyaromatic hydrocarbons using pure carbon dioxide and methanol modified carbon dioxide. The technique is capable of determining down to lOOmg kgy1 polyaromatic hydrocarbons in soils. 

Lopez-Avila et al. [59] used microwave assisted extraction to assist the extraction of polyaromatic hydrocarbons from soils. Another extraction method was described by Hartmann [60] for the recovery of polyaromatic hydrocarbons in forest soils. The method included saponification of samples in an ultrasonic bath, partitioning of polyaromatic hydrocarbons into hexane, extract cleanup by using solid-phase extraction, and gas chromatography-mass spectrometric analysis using deuterated internal standards. Polyaromatic hydrocarbons were thermally desorbed from soils and sediments without pretreatment in another investigation [61]. 

Hawthorne et al. [53] compared supercritical extraction with chlorodifluoromethane, nitrous oxide and carbon dioxide for the extraction of polychlorobiphenyls and polyaromatic hydrocarbons from soil. Chlorodifluoromethane provided the highest recoveries while methanol modified carbon dioxide gave a 90% recovery of polychlorobiphenyls from soil. 

Lagenfeld et al. [116] studied the effect of temperature and pressure on the supercritical fluid extraction of polychlorobiphenyls and polyaromatic hydrocarbons from soil. At 50°C raising the pressure from 356 to 650atm had no effect on recovery of polychlorobiphenyls. A temperature of 200°C was necessary for effective extraction. 

The extraction of polyaromatic hydrocarbons from soil and urban particulates by superheated water was reported in 1994 [17]. Extraction of compounds up to ben-zo[a]pyrene was virtually complete in 15 min at 250°C, with a flow rate of 1 ml mim and a sample of 0.5 g. Good but less complete results were obtained when extracting urban air particulates. The pressure did not influence the extraction behavior, provided it was sufficient to maintain water as a Hquid. The extraction of polychlorinated biphenyls from soil and a river sediment was also found to be complete in 15 min at 250°C [18]. Work with a wider range of compounds showed that extraction was class selective [6, 19], with phenols and Hghter aromatics being extracted at 50 to 150°C, polyaromatic hydrocarbons and lighter ahphatics at 250 to 300°C, but the heavier ahphatics only removed by steam at 250 to 300°C. This selectivity has been compared to other extraction methods [20]. The extraction of agrochemicals from soil has also been studied [6]. 

Fowlie and Bulman [43] have carried out a detailed study of the extraction of anthracene and benzo[tf]pyrene from soil. They carried out a replicated [24] factorial experiment using Soxhlet extraction and Polytron techniques. Soxhlet extraction followed by thin layer chromatography gave higher recoveries of the two polyaromatic hydrocarbons. 

Lopez-Avila et al. [25] studied the microwave assisted extraction of polyaromatic hydrocarbons, phenols and organochlorine insecticides from standard reference soils and sediments. 

The Basic Extractive Sludge Treatment (B.E.S.T. ) process is an ex situ solvent extraction technology. The B.E.S.T. process uses one or more secondary or tertiary amines, such as diisopropylamine, to separate contaminants from soil, sediment, and sludge. This technology is applicable to most organics or oily contaminants, including polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pesticides, herbicides, dioxins, furans, and other organic compounds. 

Supercritical C02 has also been tested as a solvent for the removal of organic contaminants from soil. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlorinated biphenyls (PCBs), may be removed from soil samples (77). Supercritical C02 can also extract from soil the following hydrocarbons, polyaromatic hydrocarbons, chlorinated hydrocarbons, phenols, chlorinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

These compounds are another example of nonionic, nonpolar compounds. They are found in trace levels in water and result from combustion processes and hydrocarbon spills. They are trace enriched from water by sorption onto CN, C-8, or C-18 and elution with ethyl acetate/toluene. Toluene is added to the ethyl acetate eluent to increase solubility of the polyaromatic hydrocarbons (PAHs) and to enhance elution from the solid phase. The more hydrophobic PAHs, such as pyrene (Fig. 7.11), will recover more efficiently from a more polar reversed phase, such as CN or C-8 due to less strong van der Waals interactions between the analyte and the sorbent. The PAHs may be analyzed by either GC/MS or by HPLC. Soil samples may be processed as in Section 7.10.2 with 90% methanol extraction, followed by dilution with... 

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