Design for on-line coupling of supercritical fluid extraction with liquid chromatography: quantitative analysis of polynuclear aromatic hydrocarbons in a solid matrix

Supercritical fluid extraction (SFE) was directly coupled with high-performance liquid chromatography (LC) via the simplest interface--only one six-port injection valve. By using water to eliminate decompressed CO2 gas in the solid-phase octadecylsilica trap, high extraction recovery (> or = 95%) of polynuclear aromatic hydrocarbons (PAHs) from a sand matrix was achieved under optimized conditions. The volume of rinse water had little influence on the recovery, due to the very low solubility of PAHs in water and the sorption properties of the C-18 trap. Different amounts of sand matrix with a fixed mass of analytes have also been tested. No decrease in recovery was found when the matrix (sand) increased from 1 to 10 g. Methanol and acetone were used as a CO2 modifier to enhance the extraction efficiency. Finally, PAHs in naturally contaminated soil were successfully extracted and quantitatively determined by this hyphenated system. Compared to the EPA method (Soxhlet extraction following by GC/MS), on-line SFE-LC gave precise results in a much shorter time.     

Microwave-assisted extraction of polycyclic aromatic hydrocarbons from marine sediments using nonionic surfactant solutions

Microwave-assisted micellar extraction (MAME) has been tested for the recovery of polycyclic aromatic hydrocarbons (PAHs) present in samples of marine sediments. An aqueous solution of the nonionic surfactant polyoxyethylene(23)dodecyl ether (Brij 35) was employed as the extracting medium. The proposed approach showed recovery efficiencies comparable to those afforded by the Soxhlet technique with organic solvents, but a neat reduction of the extraction times and a better reproducibility were observed. A MAME-based protocol was successfully applied for the analysis of a certified sample.     

Approach for independent-matrix removal of polycyclic aromatic hydrocarbons from solid samples based on microwave-assisted Soxhlet extraction with on-line fluorescence monitoring

A flow injection interface for fluorometric monitoring of focused microwave-assisted Soxhlet extraction (FMASE) is presented. This assembly allows real-time on-line monitoring of the PAHs extracted from solid samples in each Soxhlet cycle and provides qualitative and semi-quantitative information from natural and spiked samples. Hence, the extraction kinetics can be followed and the end of the leaching step determined independently of the sample matrix, thus avoiding excessive extraction times. The research also involves the study of the multivariate effects of the FMASE parameters by a central composite design. The method was applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation. The total content of each analyte was determined by HPLC-fluorometric detection, and the results obtained demonstrated that FMASE is a technique as efficient as conventional Soxhlet to extract PAHs from soils but with a drastic reduction of both extraction time and organic solvent disposal.     

Fluorescence line narrowing spectroscopy of polycyclic aromatic hydrocarbons on solid-liquid extraction membranes

The potential of solid-liquid extraction fluorescence line narrowing spectroscopy is evaluated for screening polycyclic aromatic hydrocarbons in aqueous samples. Octadecyl silica membranes are used with the dual purpose of sample preconcentration and solid substrate for spectroscopic measurements. 4.2 K fluorescence line narrowed spectra are directly recorded from the membrane with the aid of a fiber-optic probe. The experimental procedure is free from organic solvents and takes less than 5 min per sample. With 10 mL of water sample, the limits of detection are at the parts-per-billion level. Qualitative analysis is based on wavelength time matrices, which provide a unique format for compound identification based on spectral and lifetime data. The selectivity of this approach is demonstrated with the unambiguous determination of naphthalene in a heavily contaminated water sample.     

Pressurized hot water extraction with on-line fluorescence monitoring: a comparison of the static,dynamic, and static-dynamic modes for the removal of polycyclic aromatic hydrocarbons from environmental solid samples

A comparison of the feasibility of the three operational modes of pressurized hot solvent extraction (PHSE) (namely, static, where a fixed extractant volume is used; dynamic, where the extractant continually flows through the sample; and static-dynamic mode, which consists of a combination of the two previous modes) for the extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental solid samples (such as soil, sediment, trout, and sardine) has been performed. In all cases, a sodium dodecyl sulfate (SDS) aqueous solution was used as leaching agent. The use of a flow injection manifold between the extractor and a molecular fluorescence detector allowed real-time on-line fluorescence monitoring of the PAHs extracted from the samples, thus working as a screening system and providing qualitative and semiquantitative information on the target analytes extracted from both natural and spiked samples. The on-line monitoring option allowed the extraction kinetics to be monitored and the end of the leaching step to be determined independently of the sample matrix, thereby reducing extraction times. Efficiencies close to 100% have been provided by the three modes, which differ in the extraction time required for total removal of the target compounds. The time needed for the dynamic mode was shorter than that for the static mode. However, the establishment of a static extraction step prior to dynamic extraction was the key to shorten the time required for complete extraction. The method has been applied to a certified reference material (CRM 524, BCR, industrial soil/organics) for quality assurance/validation.     

Application of solid-phase extraction to determination of polycyclic aromatic hydrocarbons in sewage sludge extracts

The study presents the efficiency of sewage sludge sample clean-up with the application of SPE columns with various types of adsorbents. Six columns were tested: C8-octyl, C18 PolarPlus, C18-octadecyl, silicagel (SG), phenyl, cyano. The highest efficiency of recovery was observed for C18-octadecyl. Then, using C18, the method was optimised by changing the following parameters: eluent type and volume, column drying and effect of washing of cartridge.     

Emission of polycyclic aromatic hydrocarbons from the pyrolysis of liquid crystal wastes

A liquid crystal display can be described as a panel consisting of two plates of glass with liquid crystals in the space between. Generally, the liquid crystal wastes are extracted and separated into various fractions. Some recyclable materials, i.e., metals, glass, plastics, etc., are recycled, but the liquid crystals are incinerated. The emission factors for 16 U.S. EPA priority polycyclic aromatic hydrocarbons (PAHs) from the combustion of liquid crystal are approximately 390 and 1520 times higher than that of waste terephthalic acid and biological sludge combustion, respectively. In this study, we determined the emission of PAHs from the liquid crystals pyrolysis. We also investigated the fragments and gas compositions using on-line thermogravimetry–mass spectrometry (TG–MS). A temperature series of 14 fragments was analyzed in nitrogen, and was found to include m/z: 30, 32, 42, 44, 55, 57, 67, 81, 95, 109, 128, 166, 178, and 202. The fragments at m/z 32 represents formaldehyde and the fragment at m/z 44 is carbon dioxide. The fragments at m/z 55, 57, 67, 81, 95, and 109 represent hydrocarbon components, all of which may be liquid crystal by products. The TG–MS as analyzed above can offer a better understanding of the mechanisms of byproduct formation in liquid crystal waste pyrolysis.Experimentally, not detected (n.d.) −5.98 and n.d. −20.2 μg/g of 16 PAHs, in the particulate and gas phases, respectively, are determined from the emission of liquid crystal waste pyrolysis. The PAH profiles showed a predominance of naphthalene (42.6%) and phenanthrene (13.5%). The total PAH emissions for the 16 species were 7.75 and 44.05 μg/g in the particulate and gas phases, respectively, significantly lower than the values associated with liquid crystal combustion. From the viewpoint of PAH emission control, our results suggest that the pyrolysis is a better option for the disposal of liquid crystal wastes than that of combustion.     

Determination of polycyclic aromatic hydrocarbons in drinking water samples by solid-phase nanoextraction and high-performance liquid chromatography

A novel alternative is presented for the extraction and preconcentration of polycyclic aromatic hydrocarbons (PAH) from water samples. The new approachwhich we have named solid-phase nanoextraction (SPNE)takes advantage of the strong affinity that exists between PAH and gold nanoparticles. Carefully optimization of experimental parameters has led to a high-performance liquid chromatography method with excellent analytical figures of merit. Its most striking feature correlates to the small volume of water sample (500 microL) for complete PAH analyses. The limits of detection ranged from 0.9 (anthracene) to 58 ng.L (-1) (fluorene). The relative standard deviations at medium calibration concentrations vary from 3.2 (acenaphthene) to 9.1% (naphthalene). The analytical recoveries from tap water samples of the six regulated PAH varied from 83.3 +/- 2.4 (benzo[ k]fluoranthene) to 95.7 +/- 4.1% (benzo[ g,h,i]perylene). The entire extraction procedure consumes less than 100 microL of organic solvents per sample, which makes it environmentally friendly. The small volume of extracting solution makes SPNE a relatively inexpensive extraction approach.     

Simultaneous extraction and fractionation of polycyclic aromatic hydrocarbons and their oxygenated derivatives in soil using selective pressurized liquid extraction

In this study, a selective pressurized liquid extraction (PLE) method which can extract polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (oxy-PAHs) from contaminated soil and simultaneously separate them into two fractions was developed. The method uses extraction cells packed with a chromatographic adsorbent and extraction solvents of increasing polarity. Several experiments were conducted on both spiked and authentic contaminated soil samples. Different types of adsorbents, combinations of extraction solvents, and extraction temperatures were tested in order to find a method that could fulfill the purpose of the study. The final method was based on extraction cells packed with 2% deactivated silica gel. The PAHs were extracted with cyclohexane/dichloromethane (9:1) at 120 degrees C, after which the oxy-PAHs where extracted with cyclohexane/dichloromethane (1:3) at 150 degrees C. The PAHs and oxy-PAHs were efficiently separated into two fractions, and only trace amounts of some compounds were found in the inappropriate fraction. The recoveries of the PAHs were mostly above 70% and of the oxy-PAHs, above 90%. The linearity of the method was good, and the calibration curves for most compounds had a regression coefficient better than 0.99 and an intercept close to the origin of coordinates. When the selective PLE method was applied to seven authentic soil samples, the results were found to be in good agreement with those of a reference method based on Soxhlet extraction and silica gel cleanup and also in good agreement with the certified reference values available for one of the soils. The selective PLE method is faster and consumes less solvent than a traditional method based on separate extraction and fractionation steps. The selective PLE method is, therefore, suitable for the concurrent analysis of PAHs and oxy-PAHs during large-scale soil contamination studies. This will provide more information about the soil contamination and the levels of toxicity than an ordinary PAH analysis.     

Sorption of polycyclic aromatic hydrocarbons on particulate organic matters

Particulate organic matter (POM) is a key organic matter fraction which can influence soil fertility. Its interactions with hydrophobic organic pollutants (HOCs) have not been characterized and the mechanisms of retention of HOCs by POM remain unclear. In the present study, sorption behaviors of polycyclic aromatic hydrocarbons (PAHs) naphthalene (NAP), phenanthrene (PHE), and pyrene (PYR) by POMs separated from different soils were examined and the POMs were characterized by elemental analysis, solid state ¹³C NMR, and Fourier transform infrared spectroscopy (FT-IR). The results indicated that POMs were mainly composed of aliphatic components with high polarity. The different original POMs showed similar chemical composition and configuration. Sorption behaviors of PAHs indicated that there was no significant difference in sorption capacity among the POMs. Sorption of NAP and PHE by POMs displayed a nonlinear isotherm, while sorption of PYR yielded a linear isotherm. No significant hysteresis and ionic strength effect were observed for PAH desorption from the POMs.     

Detection of polycyclic aromatic hydrocarbons using quartz crystal microbalances

A chemically coated piezoelectric sensor has been developed for the determination of PAHs in the liquid phase. An organic monolayer attached to the surface of a gold electrode of a quartz crystal microbalance (QCM) via a covalent thiol-gold link complete with an ionically bound recognition element has been produced. This study has employed the PAH derivative 9-anthracene carboxylic acid which, once bound to the alkane thiol, functions as the recognition element. Binding of anthracene via pi-pi interaction has been observed as a frequency shift in the QCM with a detectability of the target analyte of 2 ppb and a response range of 0-50 ppb. The relative response of the sensor altered for different PAHs despite pi-pi interaction being the sole communication between recognition element and analyte. It is envisaged that such a sensor could be employed in the identification of key marker compounds and, as such, give an indication of total PAH flux in the environment.     

Assessment of colloid formation and physical state distribution of trace polycyclic aromatic hydrocarbons in aqueous samples.

A tandem-cartridge system was established for studying colloid formation and physical state distribution of trace polycycic aromatic hydrocarbons (PAHs) in water. The effectiveness of the method for measuring the trace PAH colloids was demonstrated. With aqueous samples prepared by adding the PAH solutes with a small amount of organic solvent carrier, the potential of colloid formation increased with the hydrophobicity and concentration of the solute, but the incipient concentration for the colloid formation may be far lower than the aqueous solubility of the solute. After formation in water, the colloids showed remarkable stability at room temperature, and the stability was greatly reduced by elevated temperature and the presence of a small amount of inorganic electrolytes. The possible mechanism of destabilization of the colloids was discussed, and the mechanism might be of utility in providing insights into the physical state distribution of the solutes in various water samples. However, further effort to investigate the mechanism through fluorescence spectrophotometry was unsuccessful. The significance of the colloid formation in methods of preparation of aqueous samples and for measuring aqueous solubilities of PAHs and other hydrophobic compounds was illustrated. The results of this work demonstrate that it is undesirable to prepare aqueous solutions of PAHs or similarly hydrophobic compounds by vigorous mixing or the use of cosolvents, methods that are widely used in many studies for which aqueous solutions of such analytes are required.     

Decreasing polycyclic aromatic hydrocarbons emission from bitumen using alternative bitumen production process

In 1988, the National Institute for Occupational Safety and Health (NIOSH) recommended that bitumen fumes should also be considered a potential occupational carcinogen and management practices such as engineering controls should be implemented. Changing the production process of bitumen, as a source control method, was investigated in our study. For the first time, a novel alternative process was used to produce paving grade bitumen with decreased PAH emissions as well as improved bitumen performance grade (PG). Post-consumer latex and natural bitumen (NB) were used as additives to obtain 60/70 modified bitumen directly from the vacuum bottom (VB) without any need for air-blowing. The emissions were produced by a laboratory fume generation rig and were sampled and analyzed by GC-Mass and GC-FID as described in NIOSH method 5515. The PG of the resulting modified 60/70 bitumen in this study covers a wider range of climatic conditions and has higher total resistance against deformation than conventional 60/70 bitumen. The total PAH emissions from modified 60/70 bitumen (100.2619 ng/g) were decreased approximately to 50% of PAHs emitted from conventional 60/70 bitumen (197.696 ng/g). Therefore, it is possible to obtain modified bitumen with lower PAH emissions and better quality than conventional bitumen via additives and without air-blowing.     

Ex-situ bioremediation of polycyclic aromatic hydrocarbons in sewage sludge

Polycyclic aromatic hydrocarbons (PAH) are regarded as environmental pollutants. A promising approach to reduce PAH pollution is based on the implementation of the natural potential of some microorganisms to utilize hydrocarbons. In this study Proteiniphilum acetatigenes was used for bioaugmentation of sewage sludge to improve the PAH removal. Bioaugmentation experiments were performed in parallel semi-continuously fed reactors started up with digested primary and secondary sludge. Three bioaugmentation approaches were investigated: A1, addition of bacteria once during starting up; A2, addition of bacteria at the beginning and then every 2nd day and A3, addition of encapsulated bacteria once during starting up. Removal of PAH was found to be both biotic and abiotic. All three approaches had a positive effect of the biological removal of PAH. Highest biological removal of individual PAH (up to 80%) was observed using continuous addition (approach A2) of the bacteria to the reactors. In general, the effect of bioaugmentation was higher in the reactors fed with primary sludge compared to the reactors fed with mixed sludge. Bioaugmentation resulted in biological removal of low molecular weight PAH in the reactors fed with primary sludge using all three approaches while clear biological removal of the medium- and high molecular weight PAH only was observed if the bacteria were added continuously (approach A2).     

Pollution patterns of polycyclic aromatic hydrocarbons in tobacco smoke

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke of 12 commercial brand cigarettes were determined in a simulated chamber of 20.25 m3 in size. The total concentrations of 17 PAHs (summation operatorPAHs) in the chamber were 3500 and 1152 ng/m3 in vapor phase and particulate phase, respectively. In vapor phase, the yield of naphthalene (NA) appeared to be the most abundant (2462 ng/cig) followed by fluorene (FLUOR) and acenaphthylene (ACY), while the yield of benzo[ghi]perylene (BP) was the most abundant (259.7 ng/cig) in particulate phase followed by phenanthrene (PHEN) and FLUOR. The proportion of PAHs in particulate phase increased with increasing molecular weight. PAHs with two to six rings accounted for 40.2%, 35.3%, 11.7%, 7.6%, 5.2% of summation operatorPAHs, respectively. There was no obvious correlation between PAHs, benzo[a]pyrene (BaP) concentrations in tobacco smoke and smoking tar contents, nicotine contents. With the source fingerprint of PAHs in tobacco smoke, NA could be regarded as the marker of tobacco smoke source because of its largest contribution to summation operatorPAHs (40.2%), followed by FLUOR (12.7%) and ACY (9.8%). Further study indicated that more than 80% of BaP in indoor air of resident homes in Hangzhou was from tobacco smoke.     

Structures and electronic properties of thin-films of polycyclic aromatic hydrocarbons

We report the fabrication and characterization of organic thin-film transistors (TFTs) using several polycyclic aromatic hydrocarbons (PAHs). Pentacene, ovalene, dibenzocoronene and hexabenzocoronene were deposited as organic semiconductors on silicon wafers with gold electrodes as the bottom-contact configuration of the TFTs. The pentacene TFT showed the highest field-effect mobility of more than 0.1 cm²/Vs in comparison with the other PAHs. The results clarified that the high field-effect mobility of the pentacene thin film is due to large grain size and intrinsic electronic properties.