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Development of an Instrumental Fractionation and Quantitation Scheme for Selected Polynuclear Aromatic Hydrocarbons Present in Extracts from Wood-Preserving Waste K

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Development of an Instrumental Fractionation and Quantitation Scheme for Selected Polynuclear Aromatic Hydrocarbons Present in Extracts from Wood-Preserving Waste K DEVELOPMENT OF AN INSTRUMENTAL FRACTIONATION AND QUANTITATION SCHEME FOR SELECTED POLYNUCLEAR AROMATIC HYDROCARBONS PRESENT IN EXTRACTS FROM WOOD-PRESERVING WASTE K. Washburn, H. Huebner, S. Safe, T. Phillips, and K.C. Donnelly*, Texas A&M University, College Station, TX, 77843-4458, Phone: 409-845-7956, FAX: 409-847-8981 ABSTRACT The polynuclear aromatic hydrocarbons (PNAs) are components of wood- preserving waste (WPW) which is known to contain multiple classes of organic and inorganic compounds. Identification and quantitation of individual PNAs and classes of PNAs is a preliminary step in assessing both the health risk associated with WPW as well as remediation efficacy. Ag+ from AgNO3 interacts with the conjugated π electrons of PNAs, allowing for a chromatographic separation based on differing degrees of conjugation. In this study, a high-volume, low-pressure (HVLP) chromatographic system comprised of a 0.5 meter, high-bore AgNO3/silica-packed column (in-house) and a Waters 600 HPLC system was used in tandem with a tunable (200-800 nm) photodiode-array detector (Waters 996) to offer a comprehensive instrumental package capable of separating PNAs by degree of aromaticity and identifying and quantifying individual components. The system was used to separate and quantify 115 individual PNAs from a complex WPW-extract. Sub-fractions collected were rich in 2-ring, 3-ring, 4-ring, 5-ring, and >5-ring PNA components. Fractionated sample material may facilitate testing in a range of biological systems to determine potential interaction of PNAs by class and establish the contribution of each to the toxicity of the whole. Additionally, the data may allow for a more comprehensive risk assessment based on constituent PNAs. While the first separation was very tedious, later separations can be tailored to collect specific subfractions of interest. This research was funded by NIEHS grant P42-ES04917. KEYWORDS: polycyclic aromatic hydrocarbons, HPLC, separation, detection INTRODUCTION associated with complex mixtures is likewise difficult due to the possible interactions of The exposure of human populations to toxic those constituents and the toxicological organic compounds occurs mainly in the effects they may promote. Therefore, form of complex chemical mixtures rather methods are needed that allow the than individual chemicals [1]. As a result, fractionation of complex mixtures into many researchers today are faced with the distinct chemical classes. challenge of accurately characterizing environmental samples in terms of both Chemical fractionation studies utilizing chemical content and, ultimately, Salmonella mutagenicity assays have shown toxicological effects. Chemical analysis that a few compounds in a complex mixture alone is an extremely difficult undertaking are responsible for the majority of the considering all of the possible constituents of mutagenic activity induced by the whole a given complex mixture. Assessing the risk mixture [2, 3]. More recently, bioassay- *To whom all correspondence should be addressed (email: [email protected]). directed fractionation research [4] has extraction methods for the subsequent demonstrated that much of the mutagenic chemical and biological analysis of ambient activity induced by environmental samples air particulate extracts have also been used can be attributed to particular classes of [20]. Current separation techniques offer chemicals within each mixture. Such much needed approaches to the separation, findings support the utility of chemical identification, and quantitation of individual separation methods to divide mixtures of components in complex mixtures. However, chemicals into less complex subfractions for current approaches are based on costly and further study. These separations allow for a labor-intensive techniques which do not more accurate characterization of mixture yield quantities of subfractions necessary for components and toxicological interactions. biological testing. In order to facilitate the identification of In this paper, the authors describe an individual chemicals and provide a better integrated multi-step chromatographic analytical scenario for quantifying those method developed specifically for PNA chemicals of interest, various analytical analysis. This method was used to separate methods have been developed to separate and quantify 115 individual PNAs from a crude mixtures into less complex fractions. complex wood-preserving waste (WPW) Previous studies on chemical separation which is known to contain multiple classes procedures have included fractional of polycyclic aromatic compounds. Fractions distillation of coal liquids [5, 6], size were chemically much less complex than the exclusion chromatography [7, 8], solvent starting crude material and were more extraction [9, 10], adsorption definable in terms of chemical composition chromatography with alumina and/or silica and quantity. The described method may be [11, 12], normal phase high performance used for generating relatively large quantities liquid chromatography (HPLC) [13, 14], and of fractionated sample material which will reverse phase HPLC [15]. Analytical facilitate testing in a range of biological methods using tandem separation methods systems. are often required for a more complete chemical characterization and subsequent PROCEDURES biological testing of highly complex mixtures. Multidimensional coupled-column All solvents used, including water, were HPLC techniques to produce distinct HPLC grade (Fisher Scientific, Pittsburgh, fractions have been utilized in the analysis of PA) and used without further purification or PNAs from complex coal liquids [16, 17]. analysis. The 115 toluene-solvated PNA Other studies have demonstrated the standards were purchased from efficacy of a multi-step methodology for AccuStandards (New Haven, CT). Other separating solvent-refined coal material standard chemicals used, including AgNO3, using fractional distillation followed by silica, HNO3, and NaOH, were purchased adsorption chromatography on neutral from Sigma Chemical Co. (St. Louis, MO). alumina with subsequent reverse phase HPLC [18]. More recently, nonaqueous ion- WPW extraction and solvation exchange separation techniques have been A 1.5 g sample of homogenized WPW was utilized for bioassay-directed fractionation sequentially extracted with 100 ml of 0.1 N of wood smoke particle extracts [19]. HNO3 and 0.1 N NaOH to remove residual Nonaqueous anion-exchange solid phase polar components. Water was used to remove residual polar components as well as column used was a 15 cm x 3.9 mm PNA residual base. This neutral WPW fraction (modified silica) column (Restek, Belefonte, was allowed to settle, and excess water was PA). Automated sample injection was decanted. The sample was then dried in a performed with a Millipore (Bedford, MA) dessicator over CaCl2 for 2 h. The resulting WISP 710B autoinjection system with a 20 1.3 g of dry neutral WPW residue was µl injection volume. The solvent system was solvated in petroleum ether to a total volume 50% acetonitrile/50% water (2 ml/min) of 5 ml. linearly ramped to 100% acetonitrile at 25 minutes with a 10 minute hold. Photodiode Sorbent preparation array scans were collected from 200-600 nm with 2 nm resolution. The target PNAs One 100 g preparation of silica/AgNO3 (10:1) sorbent was prepared as described present in each aliquot were identified and previously [21] and stored in amber glass quantified. A running total and temporal elution profile for each analyte was under N2 at 4ºC. recorded. Eluant from the second and third Chromatographic elution replicates was collected as 2-ring, 3-ring, 4- ring, 5-ring, and >5-ring subfractions for A 0.5 m (1.5 cm id) glass column (Bio-Rad future analysis and biological testing. Laboratories, Melville, NY) was filled with 28.5 g of silica/AgNO3 sorbent and RESULTS uniformly packed by elution with petroleum ether. The resulting low-pressure Sequential extraction of WPW with 0.1 N chromatographic column was fitted with acid and 0.1 N base allowed for the removal HPLC-compatible inlet and outlet fittings, of an average of 17.5% of the total mass of jacketed with aluminum foil, and clamped WPW as polar components. An elution into a vertical position. The 5 ml of solvated profile for 115 target PNAs was established WPW was placed on column and the inlet after the removal of the toluene baseline. was connected to a Waters 600 Controller The first 50 aliquots of petroleum ether- (Bedford, MA); the outlet was connected to eluted components contained the 2-ring a Waters fraction collector. Petroleum ether (represented by naphthalene, methylated was introduced at 2 ml/min and eluant was naphthalenes, and biphenyls), 3-ring collected in 3 ml aliquots. After the addition components (represented by anthracene, of 150 ml of petroleum ether, 10% water acenaphthalene, etc.) and 4-ring components was added to the solvent system to (represented by chrysene). The 5-ring deactivate Ag+-PNA complexes and allow (represented by benzo(a)pyrene, for the elution of more aromatic PNAs. Each benzo(e)pyrene, pentacene, etc.) and >5- collected fraction was air-dried and solvated ring (represented by dibenzanthracene with toluene. Any residual water was congeners) did not elute until water was removed, and an aliquot was collected for introduced to deactivate the sorbent-PNA analysis. complex. Total yield of target PNAs and substituted PNAs was 1.7% (m/m) with Analysis naphthalene being the most prevalent target PNA and picene being the
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