Application of solid phase extraction (SPE) method in determining polycyclic aromatic hydrocarbons (PAHs) in river water samples

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1 Vol. 5(11), pp , December, 2013 DOI: /JECE ISSN X 2013 Academic Journals Journal of Environmental Chemistry and Ecotoxicology Full Length Research Paper Application of solid phase extraction (SPE) method in determining polycyclic aromatic hydrocarbons (PAHs) in river water samples Shadung J. Moja 1 * and Fanyana Mtunzi 2 1 Department of Environmental Sciences, Florida Campus, University of South Africa, Florida, South Africa. 2 Department of Chemistry, Faculty of Applied and Computer Sciences, Vaal University of Technology, Vanderbijlpark, South Africa. Accepted 27 November, 2013 Trace levels of PAH pollutants are difficult to detect in water samples due to their low solubility. During this study, SPE method was used to improve the detection of the PAH analytes. A Visipre SPE vacuum manifolds sample preparation method was used to clean-up the river water samples before analysis. Twelve samples were simultaneously extracted via the unit. This method is generally faster and significantly increases sample throughput, while decreasing sample preparation hands-on time which is common for methods such as liquid-liquid extraction. An Agilent 1100 Series High Performance Liquid Chromatography (HPLC) was used to analyze trace levels of PAH compounds in river water samples before and after SPE treatment. Chromatograms of samples which were analyzed before treatment with the SPE method were simple, lacked details and could be mistaken as uncontaminated. However, after sample treatment, new peaks appeared which were well separated and relatively easier to identify when compared against chromatograms of PAHs standard mixtures that were prepared under the same experimental conditions. Samples had peaks with the following retention times (t R ): Ace (t R = m), Phe (t R = m), Anth (t R = m) and Fluo (t R = mins) from the Vaal river water samples; Naph (t R = mins), Ace (t R = ms), Phe (t R = m), Anth (t R = m) and Fluo (t R = m) from the Klip river water samples and Ace (t R = m), Phe (t R = m), Anth (t R = m), Fluo (t R = m), BbFl (t R = m), InPy (t R = m) from the Barrage river water samples. The SPE sample preparation method was successful in purifying and improving the detectability of PAH analytes. Key words: Solid phase extraction, LC-18 sorbent, polycyclic aromatic hydrocarbons, river water samples, high performance liquid chromatography. INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are multiple organic ring structures and some are carcinogenic (Srogi, 2007). These pollutants are mainly released via incomplete burning of organic matter (Papageorgopoulou et al., 1999). Anthropogenic sources include fuel burning in homes (coal, wood, liquid paraffin, biomass); in vehicles (petrol, diesel, oil, aviation fuel); in industry (energy sector, mining, manufacturing); in waste treatment (waste water, landfill, incinerators) and other burnings (tyre, vegetation) (USGS, 2013; Kan et al., 2012; Annegarn and Scorgie, 2002). PAHs are found in environmental medium such as air, soil and water (Kabziński et al., 2002). Solid-phase extraction (SPE) is an extraction and pre- *Corresponding author. mojasj@unisa.ac.za and shadung@yahoo.com.

2 Moja and Mtunzi 279 concentration technique that has been used successfully when trace levels of organic compounds were characterized (Poppa et al., 2000; Supelco, 1998). SPE is a five-step sequential method which includes adsorbent conditioning, adsorbent equilibration, sample loading, washing of adsorbent and the elution of analytes. It is a quick, selective extraction and purification sample method, which allows small volume of samples to be analysed without being pre-treated first as in liquid-liquid extraction (LLE) (Lau et al., 2010). In contrast to the SPE, the LLE method despite its low cost apparatus generates a lot of waste solvents and is time consuming (Dean, 1998). The SPE has been successfully used to extract PAHs from different environmental samples. Papageorgopoulou et al., (1999) used it to extract PAHs from airborne particulate matter; Lau et al. (2010) extracted PAHs from soil samples and Moja et al. (2013) extracted PAHs in water samples. A number of wide ranging analytical techniques that can measure the concentrations and prevalence of PAHs in different environmental matrices exist: the characterization and quantitation of PAHs, capillary gas chromatography with flame ionization detection/photoionization detection (Cam et al., 2000), supercritical fluid chromatography (Miege et al., 1999) and high performance liquid chromatography (HPLC) using mass spectrophotometric detection (Williamson et al., 2002; Andrade-Eiroa, 2010). HPLC was preferred since it gives excellent separation, good resolution and it is non destructive for the selected PAHs. The aim of this study was to improve the detectability of trace PAHs levels in river water samples by using SPE sample preparation method. MATERIALS AND METHODS Optimization of SPE adsorbent and solvents: Three 3.0 ml reverse solid phase extraction columns, Strata X mg (Phenomenox, Torrence, CA, USA), MFC mg and LC mg (Supelco, Bellefonte, PA, USA) were optimized to determine the best performing adsorbent material in retaining or recovering individual PAHs compounds with the 1.0 mg/l PAHs standard mixtures as described by Moja et al. (2013). The adsorbents were wetted and conditioned first with 5.0 ml methanol at 5.0 ml/m and equilibrated with 5.0 ml ultra-pure water at 5.0 ml/m. Columns clean-up of the water extracts were carried out using a 12-port SPE Visi-prep vacuum manifold (Supelco). A 10.0 ml blank solution was spiked with the standard solution containing mg/l PAHs and was then loaded to the columns at a flow rate of 3.0 ml/m. The lipophilic interferences were then removed by 5.0 ml of 10.0% (v/v) methanol at 5.0 ml/m. Columns were dried under vacuum for 10.0 m and then eluted by passing ml of eluting solvents at a flow rate of 1.0 ml/m (sorbents were soaked for 10.0 m with the elution solution before each elution). The eluates were collected into 2.0 ml GC vial and made up to volume with the elution solutions before being analysed by an HPLC. Care was taken that the surface of the adsorbent in the column was not dry during conditioning and loading of the sample extracts. Three different extraction solvents (methane, acetone and acetonitrile) were also optimized with the best performing adsorbent material since the extraction efficiency of PAHs depends on the nature of the solvent (Dean, 1998). The breakthrough volumes of different PAHs were determined using a sample blank. An Agilent 1100 Series HPLC was used to analyze trace levels of individual PAH compounds in water samples before and after SPE treatment. RESULTS AND DISCUSSION Calibration and choice of adsorbent material An LC-18 sorbent produced good recoveries after extracting PAHs standard mixture of 1.0 mg/l. Both PAHs analytes and LC-18 adsorbent material are nonpolar and interact with water hydrophobically (TRC, 2007). Both acetone and acetonitrile were found to be the best performing eluents, but acetone was chosen in this study because of its non-polar character, it is cheaper and is easily more accessible than acetonitrile. A ml volume of the extractant solvent was found to be the more efficient breakthrough volume when evaluated against the 1.0 mg/l PAHs standard. Linear calibration curves were obtained with linear ranges from 0 to 5.0 mg/l for napthalene and acenaphthylene, mg/l for the eight other PAHs compounds. Very good correlations were obtained with R-values ranging from during the standard calibration process. Good percentage recoveries that ranged from to % were obtained for seven compounds. Poor recoveries were also obtained for Fluo (1.03%), BbFl (0.22%) and BkFl (0.7%). The standard deviation ranged from 0.05 to 2.26 and the detection limits of less than 0.2 mg/l were obtained. An HPLC chromatogram of 10 narrow and well separated compounds of the PAHs standard mixture was obtained after passing the PAH standard mixture through the SPE adsorbent material (Figure 1). Peaks obtained with retention times (t R ) are: Naph: m; Ace: m; Phe: m; Anth: m; Fluo: m; BbFl: m; BkFl: m; BaPy: m; DiAn: and InPy: m. The analytical method development was successful as shown by relatively narrow and wellseparated peaks of individual PAH compounds. Also, a relatively flat background, which runs parallel to the x- axis, was obtained. Identities and concentrations of PAHs in river water samples The concentrations of individual PAH components were automatically calculated by Chemstation software of the Aligent HPLC used. Running the samples before SPE treatment gave rise to overlapping and broad peaks which makes it difficult to identify individual peaks, (Figure 2a-c). Overlapping peaks obtained from both the Vaal and Klip river water samples had the t R of < 5 m, while the Barrage river sample peak was wider with t R of

3 280 J. Environ. Chem. Ecotoxicol. Figure 1. A chromatogram of 1.0 mg/l PAHs standard mixture. 1 = Naphthalene; 2 = Acenaphthylene; 3 = Phenanthrene; 4 = Anthracene; 5 = Fluoranthene; 6 = Benzo(b)fluoranthene; 7 = Benzo(k)fluoranthene; 8 = Benzo(a)pyrene; 9 = Dibenz(a,h)anthracene; 10 = Indeno(1,2,3-cd)pyrene. between 0 and 25 m. But, after treating the same samples through the SPE adsorbent material, better and well separated individual chromatograms were obtained as shown in Figure 3a-c. The SPE sample preparation method cleans-up the sample matrix and pre-concentrate the water phase organics to make them detectable, which is supported in the literature (Cwiklak et al., 2009; Papageorgopoulou et al., 1999; Dean, 1998). These chromatograms are well separated and relatively easier to identify individual peaks. Ace (t R = m), Phe (t R = m), Anth (t R = m) and Fluo (t R = m) for Vaal river water samples. Klip river samples had Naph (t R = m), Ace (t R = m), Phe (t R = m), Anth (t R = m) and Fluo (t R = m). The Barrage river water samples had Ace (t R = m), Phe (t R = m), Anth (t R = m), Fluo (t R = m), BbFl (t R = m) and InPy (t R = m). A total of seven PAHs compounds were identified and quantified as was reported by Moja et al. (2013). The following PAHs were detected at the Vaal river, Klip river and Vaal barrage sampling sites: Ace was ± 0.001, ± and ± mg/l, respectively; Phe was ± 0.002, ± and ± mg/l; Anth was ± 0.001, ± and ± mg/l; and Fluo was ± 0.008, ± and ± mg/l. Naph was detected only at the Klip river site ( ± mg/l), while BbFl ( ± mg/l) and InPy ( ± mg/l) were detected at the Vaal barrage site. BkFl, BaPy and DiAn were not detected under the current experimental conditions. Based on the possible carcinogenic list of PAHs reported by MDH (2001), only BbFl and InPy were detected at the Vaal barrage site. This is significant because farmers in this region use the barrage untreated water for irrigation. The main concern lies in the fact that these carcinogenic organic compounds may find their way into the food chain. The Vaal barrage is also the main supplier of water for domestic and agricultural usage. Ineffective treatment processes of contaminated raw water will expose many users to these toxic pollutants. Since the study was undertaken in a heavily industrialized and polluted region of central South Africa, there is a very high possibility that locals will be exposed to some levels of PAHs in water and other environmental media. The region is home to iron-steel processing and metal alloy companies, a major petro-chemical company, and many other possible industrial sources of PAHs. Conclusions An LC-18 SPE sample preparation methods was able to pre-concentrate, clean-up unwanted matrix constituents and improve the detectability of trace PAH levels in river water samples. Technologies like the SPE method should be embraced since they have been found to be efficient

4 Moja and Mtunzi 281 (A) (B) (C) Figure 2. Chromatograms of (a) Vaal river water, (b) Klip river water and (c) Vaal barrage water samples before extraction and pre-concentration with SPE cartridges. purification devices (Cwiklak et al., 2009). During this research, treating water samples with the SPE method made it possible to detect traces of PAH compounds which were undetectable as was demonstrated. The SPE

5 282 J. Environ. Chem. Ecotoxicol. Figure 3. Chromatograms of (a) Vaal river water, (b) Klip river water and (c) Vaal barrage water samples after extraction and preconcentration with SPE cartridges. 1 = Naphthalene; 2 = Acenaphthylene; 3 = Phenanthrene; 4 = Anthracene; 5 = Fluoranthene; 6 = Benzo(b)fluoranthene; 7 = Indeno(1,2,3-cd)pyrene. technology makes it possible to identify organic pollutants early enough to allow authorities to take action which will prevent their spread. ACKNOWLEDGEMENT The research was supported by Vaal University of Technology and University of South Africa. All analyses were done at SASOL Labs in Sasolburg. REFERENCES Andrade-Eiroa A, Leroy V, Dagaut P, Bedjanian Y (2010). Determination of Polycyclic Aromatic Hydrocarbons in kerosene and bio-kerosene soot. Chemosphere. 78: Annegarn HJ, Scorgie Y (2002). Air quality-chemistry and physics of the atmosphere. MSc CourseWork Notes, University of thewitwatersrand.

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