Abstract In this study, caged calcium alginate-caged multiwalled carbon nanotubes dispersive microsolid phase extraction was described for the first time for the extraction of polycyclic aromatic hydrocarbons (PAHs) from water samples prior to gas chromatographic analysis. Fluorene, phenanthrene and fluoranthene were selected as model compounds. The caged calcium alginate-caged multiwalled carbon nanotubes was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermal gravimetry analyses. The effective parameters namely desorption solvent, solvent volume, extraction time, desorption time, the mass of adsorbent and sample volume were optimized. Under the optimum extraction conditions, the developed method showed good linearity in the range of 0.5–50 ng mL−1 (R2 ≥ 0.996), low limits of detection and quantification (0.42–0.22 ng mL−1) (0.73–1.38 ng mL−1) respectively, good relative recoveries (71.2–104.2%) and reproducibility (RSD 1.8–12.4%, n = 3) for the studied PAHs in water sample. With high enrichment factor (1,000), short extraction time (<30 min), low amounts of adsorbent (100 mg) and low amounts of solvent (0.1 mol) have proven that the microsolid phase extraction method based on calcium alginate-caged multiwalled carbon nanotubes are environmentally friendly and convenient extraction method to use as an alternative adsorbent in the simultaneous preconcentration of PAHs from environmental water samples. Introduction Polycyclic aromatic hydrocarbons (PAHs) are notorious environmental persistent pollutants with toxic, carcinogenic and mutagenic properties (1). So far, over 100 PAHs have been known occur naturally and 16 of them have been included in the list of priority pollutants (2). PAHs are non-polar and very hydrophobic compounds with low water solubility and restrict biodegrade due to their high stability and complex molecular structures (3). PAHs are mainly produced by human activities such as incomplete combustion of fossil fuels or carbon-containing organic substances, industrial processes, and domestic burning (4). Furthermore, due to widely waste of PAHs, they can be easily mobile into an aquatic environment and lead to human risk. Therefore, US Environmental Protection Agency (EPA) have set a maximum residual levels (MRLs) is 0.2 ng mL−1 for specified PAHs in drinking water (5). Due to high toxicity of PAHs even at trace levels, development of methodologies for the monitoring of PAHs in environment is often necessary, thus, it is one of the important aspects of environmental analytical chemistry. Sample preparation is usually necessary to separate the analyses from complex matrices or to preconcentrate them in order to improve sensitivities and detection limits (6, 7). Moreover, the classical sample pretreatment techniques such as liquid–liquid extraction (LLE) and solid-phase extraction (SPE) require high volumes of toxic reagents (8, 9). SPE has been extensively used for the preconcentration of PAHs in environmental waters (10, 11). In general, SPE is surface dependent processes since its kinetics depend directly on the contact surface between the analyses and the solid adsorbent (12). This issue becomes critical when the amount of solid adsorbent is reduced to the microscale. In recent years, increased interest in the development of environmentally friendly analytical procedures according to the rules of green chemistry has been observed for waste water recycling (13, 14). In green dispersive microsolid-phase extraction (D-μ-SPE), the small amount of solid adsorbent promotes the immediate interaction between the analyses and adsorbent in short time. After adsorption the analytes held in the solid adsorbent are eluted with small amount of suitable solvents (15, 16). In this context, nanoparticles (NPs) seem to be perfect to use in D-μ-SPE, such as fullerene (17), carbon nanotubes (CNTs) (18), graphene (19, 20) and inorganic NPs (21) including magnetic NPs (22, 23). Such NPs and waste material as adsorbent (24) can be applied in organic (25, 26) and inorganic (27) decontamination (28, 29). Recently carbon based materials namely MWCNTs have widely used as adsorbent for PAHs removal or preconcentration (30, 31). Due to chemical structures of the PAHs which are planar with benzene ring, they can form both hydrophobic interaction and strong π–π interaction with MWCNTs, the π–π bonding interaction is still strong enough to keep the analytes adsorbed on MWCNT (32–34). However, excessive use of MWCNTs has an adverse effect on living organisms (35, 36). They can enter into human pneumocystis and injure pulmonary functions (37, 38), they can be scavenged by the reticuloendothelial system from blood and accumulate in mouse liver and spleen and affect the immunity of spleen (39, 40). Because of the poor degradability (41) and toxicity of MWCNTs, they should be removed from drinking water as far as possible. However, it is difficult to remove MWCNTs from water using conventional separation methods due to their microsized structures, this limitation may be the bottleneck to obstruct MWCNTs to be widely used as adsorbents in environmental protection in the future. One effective method to resolve the second pollution caused by MWCNTs is to search for suitable supporters to immobilize MWCNTs for preparing macroscopic CNTs composites (42). In order to make full use of the current microsized MWCNTs and its supporting, the alginate is a potential candidate for MWCNTs. Alginate, the salt of alginic acid, has hydrophilicity, biocompatibility, non-toxicity and exceptional formability (43). Therefore, it has excellent characteristics to support and fix MWCNTs. The composites not only make full use of the good PAHs adsorption properties of MWCNTs and alginate, but also prevent microsized MWCNTs from breaking off the composites to cause second micropollution to water. In this study, a novel application of D-μSPE method based on Alg-MWCNT beads is presented at first time. The synthesized beads are characterized and applied for preconcentration of three PAHs from water samples. Moreover, the whole procedure is optimized in order to achieve the highest recoveries. PAHs are selected as model compounds to take into account their applications for the analysis of water samples. Experimental Reagents and materials The PAH standards, namely fluorene (FLU), fluoranthene (FLA) and phenanthrene (PHE) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Stock solutions (1,000 mg L−1 of each analyte) were prepared separately by dissolving the PHE in acetonitrile and (FLU and FLA) in methanol and stored at 4°C in the dark when not in use. Ethyl acetate (HPLC grade), methanol (HPLC grade), acetonitrile (HPLC grade), acetone (HPLC grade) and isopropyl alcohol (HPLC grade) were purchased from Merck (Darmstadt, Germany). Double-distilled, deionized water of (resistance 18.2 MΩ) was purified by Nanoultra-pure water system (Barnstead, USA). Sodium alginate was purchased from (QReC, Selangor, Malaysia). MWCNTs (specific surface area ≥233 m2 g−1, purity 95%, 8–15 nm outer diameter 50 mm in length) were purchased from Sun Nanotech (Jiangxi, China). Tap water sample was collected from our laboratory while the river water sample was collected from the UTM University River; mineral water (Ocean®) was purchased from local markets. Samples were collected in Teflon bottles precleaned with acetone and covered with aluminum foil. The samples were stored in the dark at 4°C until analysis. Instruments Perkin-Elmer spectrometer (MA, USA) was used for FTIR spectra in transmission mode and the samples were initially dried at 373 K for 24 h, ground to fine powder and mixed with KBr crystals to prepare KBr wafers. FTIR Spectra were obtained with KBr pellet in the range of 400–4,000 cm−1. A Perkin-Elmer (MA, USA) diamond TG/DTA thermal analyser was used for heating the samples in atmospheric conditions using nitrogen flow at a rate of 100 mL/min and heating rate of 10°C/min. The JSM-6710F scanning electron microscope JEOL (Tokyo, Japan) was used for the morphology. The preparation of Alg-MWCNT microbeads Sodium alginate (Na-Alg) was dissolved in deionized water at a concentration of 1.5 mg mL−1. MWCNTs was dispersed into Na-Alg solution and mix thoroughly by high stirring (900 rpm) and then by ultrasonication. The suspension was mixed into CaCl2 (0.2 M) drop by drop using syringe (0.8 mm diameter needle).The gel beads were allowed to stay in solution for 6 h to stabilize.Finally, the beads were washed with distilled water in order to remove excess CaCl2 and dried in oven at 80°C for 48 h (Figure 1). Figure 1. View largeDownload slide Schematic of the preparation of calcium alginate MWCNT microbeads. Figure 1. View largeDownload slide Schematic of the preparation of calcium alginate MWCNT microbeads. Chromatographic conditions A 7820A gas chromatograph equipped with a flame ionization detector (GC-FID), from Agilent (Santa Clara, CA, USA) was used for the identification of three PAHs in the water samples. Helium was used as the carrier gas at a constant flow rate of 1 mL min−1. Splitless injection was performed at 250°C and the injection volume was 1 μL. The chromatographic separation of PAHs was performed on a HP-5.5% phenyl methyl siloxane column (30 m × 0.25 mm ID, 0.25 μm film thickness) from Agilent. The oven temperature was programmed from 150°C for 3 min, and then increased to 250°C at 20°C min−1 for 2 min. The injection port temperature was set at 250°C and FID detector was set at 300°C. The hydrogen and air flow rates were set at 40 and 400 mL min−1, respectively Optimization of effective parameters on extraction performance The effective extraction parameters on D-μ-SPE performance were optimized using change one variable at a time (OVAT) method. Initially 50 mL sample volume was spiked 200 ng mL−1 of three PAHs, then 50 mg of adsorbent was added into the mixture and for 10 min at extraction time, followed by desorption (2 min) of analytes using 0.5 mL of different type of solvent (methanol, isopropanol, hexane, acetone, acetonitrile and ethyl acetate) directly inject to the instrument. The other parameters were changed OVAT as follows; volume of solvent (100–500 μL), extraction time (5–50 min), desorption time (1–15 min), different amount of adsorbent (25–200 mg) and sample volume (10–300 mL). Extraction procedure Under the optimum condition, 100 mg of synthesized Alg-MWCNT beads were dispersed into a 100 mL aqueous sample water sample spiked with 10 ng mL−1 of the mixed three PAHs solution (FLU, FLA and PHE). The mixture was shaken on a platform shaker for 30 min, the Alg-MWCNT beads were tumbled freely in the sample solution during the extraction to facilitate mass transfer. The aqueous layer was decanted, because the Alg-MWCNT beads were much heavier than water, hence, easy to isolate them from the aqueous phase. The beads were dried by placing in a lint-free tissue to remove excess moisture. The Alg-MWCNT beads were totally transferred to microcentrifuge tube. Finally, 0.1 mL ethyl acetate was added to the centrifuge tube and desorbed analytes by conventional ultrasonication using a Bransonic 3510E-DTH ultrasonic cleaner (Branson Ultrasonics, Danbury, USA) for 5 min. The desorption solution was collected using a micropipette, 1 μL of the solution which was injected into the GC-FID system for analysis (Figure 2). Figure 2. View largeDownload slide Schematic of Alg-MWCNT D-μ-SPE extraction procedures. Figure 2. View largeDownload slide Schematic of Alg-MWCNT D-μ-SPE extraction procedures. Validation of analytical method The validation of Alg-MWCNT-D-μ-SPE was carried out in terms of linearity, LODs (3 × S/N, n = 3), LOQs (3.33 × LOD) and enrichment factor (EF = Vaq/Vorg), where Vorg is the volume of organic solvent as eluent and Vaq is the initial volume of water sample. precision (%RSD) and recovery (%R). Precisions (%RSD) were expressed in the intra- and inter-day precisions by performing three replicates (n = 3) analyses for every concentration of spiked water samples on the same day and over 3 different days (n = 9). Recovery was calculated as the percentage of mean concentration of target analytes found after extraction (derived from the plotted matrix-matched calibration curve) against the concentration spiked in the sample. Real sample analysis The real samples were analyzed in two steps using unspiked and spiked process. First 100 mL of water samples (without analytes)were treated using the extraction procedure as described in Extraction procedure. Second, the samples were spiked with standard solution (10 ng mL−1) of three PAHs followed by an extraction process described in Extraction procedure. Results Effect of the percentage of MWCNT in synthesized adsorbent The MWCNTs is the key factors in adsorption of PAHs from aqueous media since it provide strong π–π interaction. Optimum dosage of MWCNTs in prepared beads (Alg-MWCNT) was carried out via immobilizing different percentage of MWCNTs within alginate in the range of 0–30% (w/w). The extraction peak areas were increased when the 20% (w/w) MWCNTs was used (Figure 3), thereafter, it decreased since MWCNT’s aggregation and surface reduction occurred, because surface area or concentration of alginate were constant during this process (44). Therefore, PAHs were tended to be entrapped in closed interstitial spaces between aggregates (45) then desorption become incomplete. Figure 3. View largeDownload slide Effect of MWCNT percentage on extraction of PAHs from water sample. Conditions: sample volume, 50 mL; analyte concentration, 200 ng mL−1 (FLU, PHE and FLA); eluent, methanol; eluent volume, 500 μL; adsorbent dosage, 50 mg; extraction time,10 min; desorption time, 2 min. Figure 3. View largeDownload slide Effect of MWCNT percentage on extraction of PAHs from water sample. Conditions: sample volume, 50 mL; analyte concentration, 200 ng mL−1 (FLU, PHE and FLA); eluent, methanol; eluent volume, 500 μL; adsorbent dosage, 50 mg; extraction time,10 min; desorption time, 2 min. Furthermore, 20% (w/w) MWCNTs showed less leaching of CNTs in water samples since if MWCNT concentration exceeded 20%, leakage of CNTs was observed in filter paper and water samples, thus, caused increase in the secondary contamination in water. Thus, 20% (w/w) of MWCNTs was selected for further analysis. Characterizations FTIR spectroscopy Figure 4a shows the FTIR spectra of raw sodium alginate (Na-Alg), peaks at 3,243, 2,922, 1,634, 1,425 and 1,023 cm−1 exhibit its stretching vibrations of O–H, aliphatic C–H, O–C–O (asymmetric), O–C–O (symmetric) and C–O, respectively, which are characteristics of the polysaccharide (46, 47). Figure 4b shows raw commercial MWCNT spectra, two peaks located at 3450 and 1,634 cm−1 illustrate the O–H (stretching vibration) and C = C stretching for unsaturated aliphatic structures (48). Figure 4c shows FTIR spectra of lab-made adsorbents based on calcium alginate MWCNT composite (Alg-MWCNTs), two peaks at 1,610 and 1,416 cm−1 are reduced and also shifted due to crosslink of the carboxyl group with Ca+2. On the other hand, the FTIR spectrum of the Na-Alg is changed upon its adsorption onto the MWCNTs, probably due to hydrophobic interaction between Na-Alg and MWCNTs (49). Figure 4. View largeDownload slide FTIR spectra of (a) sodium alginate, (b) MWCNT and (c) Alg-MWCNT. Figure 4. View largeDownload slide FTIR spectra of (a) sodium alginate, (b) MWCNT and (c) Alg-MWCNT. Scanning electron microscopy Figure 5a, b and a′, b′ shows the SEM images and corresponding 3D surface maps of calcium alginate CA and Ca-Alg-MWCNTs composite bead, respectively. It can be observed that the bead surface was rough and there are many pores on the surface of Ca-Alg-MWCNTs composite in comparison to native calcium alginate CA. From the high magnification images, it can be seen that the cross section surface of calcium alginate bead (Figure 5a) was dense, as compared to that for Ca-Alg-MWCNTs composite bead (Figure 5b). The 3D surface maps of CA and Ca-Alg-MWCNTs composite bead shows that, implanted MWCNTs improve the surface area of the Ca-Alg-MWCNTs compare with CA. Thus, the results of SEM and 3D surface map studied have provided clear evidence that the doping of MWCNTs in the composite bead was enhance the surface area of Ca-Alg-MWCNTs. The diameter of the MWCNTs in beads surface is larger than that of the crude MWCNTs as the surfaces of MWCNTs are wrapped by CA (50, 51). Figure 5. View largeDownload slide Scanning electron micrographs of (a) calcium alginate ×100, (b) Ca-Alg-MWCNTs × 7,000 and 3D surface maps of (a′) calcium alginate and (b′) Ca-Alg-MWCNTs. Figure 5. View largeDownload slide Scanning electron micrographs of (a) calcium alginate ×100, (b) Ca-Alg-MWCNTs × 7,000 and 3D surface maps of (a′) calcium alginate and (b′) Ca-Alg-MWCNTs. Thermogravimetric analysis Thermogravimetric analysis was carried out with 7–8 mg samples on a platinum pan under a nitrogen atmosphere at a heating rate of 20°C min−1 until 800°C. Thermogravimetric curves of Na-Alg and Alg-MWCNTs are displayed in Figure 6A. The thermogram of Na-Alg exhibited two distinct stages of weight loss. The first with weight loss ~13% in the range of 30–168°C with a maximum decomposition rate at 82°C was assigned to elimination of water adsorbed to the hydrophilic polymer. The other weight loss ~40% in the range of 203–328°C with a maximum decomposition rate at 253°C was ascribed to a complex process including dehydration of the saccharide rings, depolymerization with the formation of water, CO2 and CH4 (52). Temperature of 50% weight loss was found to be 284°C for Na-Alg. Figure 6. View largeDownload slide Comparison of TGA (solid line) and DTG (dashed line) curves for (A) Na-Alg and (B) Alg-MWCNT, over the temperature range of 30–800°C obtained with a heating rate 20°C min−1 under N2 flow. Figure 6. View largeDownload slide Comparison of TGA (solid line) and DTG (dashed line) curves for (A) Na-Alg and (B) Alg-MWCNT, over the temperature range of 30–800°C obtained with a heating rate 20°C min−1 under N2 flow. The differential thermogravimetric curve of the Alg-MWCNT showed three degradation steps (Figure 6B). The first 0.5% weight loss in the range of 30–166°C with a maximum decomposition rate at 75°C was attributed to elimination of water adsorbed to the Alg-MWCNT structure. The second 44% weight loss in the range of 216–400°C with a maximum decomposition rate at 220°C was assigned to depolymerization with the formation of water, CO2 and CH4. The third degradation 9% weight loss in the range of 427–591°C with a maximum decomposition rate at 480°C was attributed to reaction processes secondary pyrolysis reactions, tar cracking, char formation and the degradation of thermally robust inorganic constituents (53, 54).Temperature of 50% weight loss was also found to be 462°C for Alg-MWCNT higher than Na-Alg. From the DTG curves, it can be concluded that the thermal stability of the alginate increases with the crosslinking by calcium and incorporation of MWCNT on the polysaccharide backbone. Optimization of effective parameters on extraction performance Some key factors that influence the D-μ-SPE extraction efficiency, i.e., desorption solvent, volume of solvent, extraction time, agitation mode, desorption time amount of adsorbent material and sample volume, were considered. Effect of desorption solvent Various organic solvents compatible with instrumental technique (GC-FID) were studied, namely, hexane, isopropanol, ethyl acetate, acetone, methanol and acetonitrile. In all cases, the volume was fixed at 500 μL. Ethyl acetate provided the best results in terms of chromatographic peak areas (Figure 7a) within range (55). Figure 7. View largeDownload slide Optimization of Alg-MWCNT-D-μ-SPE. (a) Effect of desorption solvent, (b) effect of desorption time, (c) effect of the extraction time and (d) effect of desorption time. Error bars represent the standard deviation, n = 3. Figure 7. View largeDownload slide Optimization of Alg-MWCNT-D-μ-SPE. (a) Effect of desorption solvent, (b) effect of desorption time, (c) effect of the extraction time and (d) effect of desorption time. Error bars represent the standard deviation, n = 3. Effect solvent volume The eluent volume was carried out in order to increase the method sensitivity and also obtaining maximum enrichment factor. Ethyl acetate volume was studied between 100 and 500 μL, the results are summarized in (Figure 7b) and 100 μL shows highest analytes preconcentration. Thereafter increase in the volume of the solvent over 200 μL may cause re-adsorption of the analyte from the adsorbent and give low recovery. Thus, 100 μL of ethyl acetate was selected as optimum and enrichment factor was obtained 1,000 (EF = Vaq/Vorg). Effect of the extraction time D-μ-SPE involves dynamic partitioning of analytes to the adsorbent. The extraction efficiency depends on the mass transfer between the Alg-MWCNT beads and the sample solution. Because mass transfer is a time-dependent process, the effect of the extraction time was investigated in the range 10–50 min (Figure 7c). The sample solution was continuously agitated at room temperature with an orbital shaker to facilitate the mass transfer process, and the agitation speed was fixed at 250 rpm. The peak areas for all PAHs increased with the extraction time up to 30 min, remaining almost constant over this value, thus, 30 min were selected as optimum. Effect of desorption time The effect of desorption time was investigated by using the ultrasonication of Alg-MWCNT D-μ-SPE in solvent for 1–15 min. It was observed that; peak areas showed an increase from 1 to 5 min (Figure 7d). This can be explain by prolonged desorption time could conceivably lead to re-adsorption of the analytes, which it is common in microextraction techniques (56–59). Based on the observation, the optimum desorption time was set at 5 min. In order to examine carryover effect, the used D-μ-SPE was further desorbed in ethyl acetate for another 5 min; no analytes were detected. Effect of adsorbents dosage The amount of adsorbent is little bit more critical than the sample amount. Insufficient amount of adsorbent causes the breakthrough of the analytes whereas higher amounts increases the cost and time of the analytical procedure. Higher amounts of adsorbent may also affect the final recoveries if the back extraction (elution) of the analytes from adsorbent is not quantitative. Optimum dosage of the adsorbent (Alg-MWCNTs) beads for the adsorption of the PAHs was investigated by using different amounts (25–200 mg) of the Alg-MWCNT beads. Figure 8a shows that the adsorption of all the three PAHs could reach the maximum plateau when the amount of Alg-MWCNT beads was increased to 25 mg. Therefore, 100 mg Alg-MWCNT beads was chosen for the further analysis. Figure 8. View largeDownload slide (a) Effect of adsorbent dosage and (b) effect of sample volume. Figure 8. View largeDownload slide (a) Effect of adsorbent dosage and (b) effect of sample volume. Effect of sample volume In order to obtain high enrichment factor, sample volume was investigated. Sample can significantly affect the recovery values and the global sensitivity of the methodology. To evaluate this effect, sample volumes of the aqueous phase in the range from 10 to 200 mL were tested (Figure 8b). The results showed that when the volume was increased from 10 to 100 mL, the peak area was increased for all analytes but beyond 100 no significate change in extraction efficiency was observed due to saturation of all active sites in the adsorbents. Method validation The analytical performance of D-μ-SPE based on Alg-MWCNTs was investigated, i.e., linearity, LOD, LOQ and precision (repeatability and reproducibility). Under optimum condition the matrix match calibration linearity was carried out for different concentration of PAHs in the range from 0.05 to 50 ng mL−1 and satisfactory coefficient of determination (R2) for all PAHs were obtained in the range of 0.9968–0.9987. Table I lists experimental results for proposed D-μ-SPE method. The good LOD (0.22–0.42 ng mL−1, 3 × S/N, n = 3) was obtained for batch wise method and LOQ was calculated 10-fold of S/N ratio. The obtained LOD for D-μ-SPE based on Alg-MWCNTs was well comparable with MRL, i.e., 0.2 ng mL−1 as set by US EPA for specified PAHs in different water samples. Repeatability and reproducibility were obtained through precision (%RSD) for different extractions (%RSD 1.8–12.4, n = 3 and 3.2–12.9, n = 9), respectively. Table I. Validation Parameter: Limit of Detection (LOD), Limit of Quantification (LOQ), Coefficient of Determination (R2), Enrichment Factor (EF) and Linearity Precision (%RSD) Analytes Linearity (ng mL−1) R2 LOD (ng mL−1) LOQ (ng mL−1) EF %RSD n = 3 Fluorene 0.5–50 0.9985 0.42 1.38 791 1.8–6.3 Phenanthrene 0.5–50 0.9968 0.30 0.99 864 3.5–11.9 Fluoranthene 0.5–50 0.9987 0.22 0.732 912 0.4–12.4 Analytes Linearity (ng mL−1) R2 LOD (ng mL−1) LOQ (ng mL−1) EF %RSD n = 3 Fluorene 0.5–50 0.9985 0.42 1.38 791 1.8–6.3 Phenanthrene 0.5–50 0.9968 0.30 0.99 864 3.5–11.9 Fluoranthene 0.5–50 0.9987 0.22 0.732 912 0.4–12.4 Real sample analysis The proposed D-μ-SPE method was applied for real sample analysis under the optimum condition. Table II reveals that the good recovery was obtained for two FLU and PHE in different samples. Matrix effects were observed for FLA in tap water and river water since a little low recovery was obtained. There was no detection of three PAHs in real samples using the D-μ-SPE based on Alg-MWCNT with 912EF and 0.22 ng mL−1 LOD. The chromatogram in Figure 9 shows spiked and unspiked real samples analysis for PAHs preconcentration using D-μ-SPE. The clear peaks provide the high selectivity and low matrix effect of proposed extraction method (D-μ-SPE-Alg-MWCNT). Table II. Analysis of Selected PAHs in Environmental Water Samples Sample %Recovery ± %RSD Mineral water Tap water River water Spiked (ng mL−1) Spiked (ng mL−1) Spiked (ng mL−1) 0 10 0 10 0 10 FLU ND 95 ± 5.1 ND 98.2 ± 4.0 ND 102 ± 1.82 PHE ND 104.2 ± 6.7 ND 82.1 ± 3.9 ND 86.1 ± 4.61 FLA ND 104 ± 7.2 ND 72 ± 1.23 ND 71.2 ± 7.26 Sample %Recovery ± %RSD Mineral water Tap water River water Spiked (ng mL−1) Spiked (ng mL−1) Spiked (ng mL−1) 0 10 0 10 0 10 FLU ND 95 ± 5.1 ND 98.2 ± 4.0 ND 102 ± 1.82 PHE ND 104.2 ± 6.7 ND 82.1 ± 3.9 ND 86.1 ± 4.61 FLA ND 104 ± 7.2 ND 72 ± 1.23 ND 71.2 ± 7.26 ND = not detected. Figure 9. View largeDownload slide GC-FID chromatograms for river water analysis (a) spiked at 10 ng mL−1 of each PAHs and (b) unspiked sample. Peak identities: 1. FLU, 2. PHE and 3. FLA. Figure 9. View largeDownload slide GC-FID chromatograms for river water analysis (a) spiked at 10 ng mL−1 of each PAHs and (b) unspiked sample. Peak identities: 1. FLU, 2. PHE and 3. FLA. Comparison of Alg-MWCNT-D-μ-SPM with other reported methods The comparison of proposed Alg-MWCNT-D-μ-SPE analytical method with other reported methods is tabulated in Table III. Infact, each method has its own advantages and disadvantages. The LOD, precision and recovery of proposed method were comparable to other reported methods (60, 61). C18/Fe3O4 based MSPE–GC–MS and Fe3O4/GO based MSPE HPLC–UV have a good potential for the separation, purification, high magnetic property to satisfy the requirement of magnetic separation (62, 63). However, it requires large volume of organic solvent 4.5 and 2 mL, respectively, which under these methods expensive and toxic to the environment in comparison with current described method. DLLME–D-μ-SPE–GC–MS and DI-HS-SPME GC–MS involve multistep operations (60, 64). HSME–GC-FID requires very costly equipment which contributes either special conditions for microsyringe needle and sample temperatures: −6 and 40°C, respectively (61). Alg-MWCNT-D-μ-SPE exhibits significant advantages including its simple operation, cost-effective, high recovery and enrichment factors and environmentally friendly as compared to other reported methods. Table III. Comparison of the D-μ-SPE Based on Alg-MWCNT With Other Published Methods for the Extraction and Determination of PAHs From Water Samples Analysis methods* LOD (ng mL−1) Dynamic linear range (ng mL−1) R2 EF %Recovery %RSD Ref. DI-HS–SPME GC–MS 0.17–0.36 0.6–10 0.99613–0.99972 60–120 5–17 (60) HSME–GC-FID 4–41 10–240 0.9887–0.9999 9–159 0.7–20.2 (61) 16–160 80–240 C18/Fe3O4 based MSPE–GC–MS 0.8–36 10–800 0.9927–0.9994 5 35–96 10 (62) Fe3O4/GO based MSPE HPLC–UV 0.09–0.19 0.5–100 0.9830–0.9993 25 76.8–103.2 1.7–11.7 (63) DLLME–D-μ-SPE–GC–MS 0.013–0.022 0.5–50 0.9932–0.9991 200 89.3–93.1 5.3–7 (64) Alg-MWCNT-D-μ-SPE–GC-FID 0.2–0.4 0.5–50 0.9968–0.9987 1,000 71.2–104 1.23–7.26 This study Analysis methods* LOD (ng mL−1) Dynamic linear range (ng mL−1) R2 EF %Recovery %RSD Ref. DI-HS–SPME GC–MS 0.17–0.36 0.6–10 0.99613–0.99972 60–120 5–17 (60) HSME–GC-FID 4–41 10–240 0.9887–0.9999 9–159 0.7–20.2 (61) 16–160 80–240 C18/Fe3O4 based MSPE–GC–MS 0.8–36 10–800 0.9927–0.9994 5 35–96 10 (62) Fe3O4/GO based MSPE HPLC–UV 0.09–0.19 0.5–100 0.9830–0.9993 25 76.8–103.2 1.7–11.7 (63) DLLME–D-μ-SPE–GC–MS 0.013–0.022 0.5–50 0.9932–0.9991 200 89.3–93.1 5.3–7 (64) Alg-MWCNT-D-μ-SPE–GC-FID 0.2–0.4 0.5–50 0.9968–0.9987 1,000 71.2–104 1.23–7.26 This study *DI-HS-SPME = direct immersion and headspace modes solid phase microextraction; Fe3O4/GO based MSPE = Fe3O4/graphene oxide nanocomposite electrostatic self-assembly magnetic solid-phase extraction. Discussion A new analytical application was developed based on dispersive microsolid phase extraction (D-μ-SPE) technique for preconcentration of PAHs from water samples. D-μ-SPE based on alginate multiwalled carbon nanotube (Alg-MWCNT) was combined with GC-FID successfully and applied in the analysis of three selected PAHs namely: fluorene (FLU), phenanthrene (PHE) and fluoranthene (FLA) in water samples. The effect of parameters such as desorption solvent, volume of solvent, extraction time, agitation mode, desorption time, amount of adsorbent material and sample volume on the extraction efficiency were investigated. Under the optimized condition, good linearity was obtained with correlations of determination, R2 ≥ 0.9968 over concentration ranges of 0.5–50 ng mL−1 for water samples. The method LODs (S/N = 3, n = 3) were in the range 0.22–0.42 ng mL−1 with high enrichment factors (up to 912). Due to satisfactory LODs and recovery, this method is highly suggested for biological sample preparation. Conclusion This investigation describes the preparation of caged calcium alginate-caged multiwalled carbon nanotubes which was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermal gravimetry analyses. The prepared caged calcium alginate-caged multiwalled carbon nanotubes proved effective in the dispersive microsolid phase extraction of PAHs from water samples prior to gas chromatographic analysis. Acknowledgments The authors thank Universiti Teknologi Malaysia and the Ministry of Science, Technology and Innovation Malaysia (MOSTI) for financial support through research Grant no. RJ130000.7909.4S069. Also thanks to the Ministry of Construction, Housing and Public Municipalities, General directorate of sewerage in Iraq for financial support for A.S. Abboud. 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Journal of Chromatographic Science – Oxford University Press
Published: Feb 1, 2018
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