Cetyltrimethylammonium Bromide-Coated Fe3O4 Magnetic

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Analytical Chemistry

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Cetyltrimethylammonium Bromide-coated Fe3O4 Magnetic

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Nanoparticles for Rapid Analysis of 15 Trace Polycyclic Aromatic

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Hydrocarbons in Aquatic Environments by UPLC-FLD

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Hao Wang,†,‡, Xiaoli Zhao,†,‡,* Wei Meng,‡,* Peifang Wang,§ Fengchang Wu,‡ Zhi Tang,‡ Xuejiao

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Han,‡ John P. Giesy£

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‡

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Academy of Environmental Sciences, Beijing 100012, China;

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State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research

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College of Water Sciences, Beijing Normal University, Beijing 100875, China;

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§

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of Education, College of Environment, Hohai University, Nanjing 210098, China;

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£

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Saskatchewan, 44 Campus Drive, Saskatoon, SK, Canada.

Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry

Department of Veterinary Biomedical Science and Toxicology Centre, University of

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*Corresponding Authors: [email protected], [email protected]

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Tel.: (+86)10-84931804; Fax: (+86)10-84931804;

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Author Contributions: †These authors contributed equally to this work

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ACS Paragon Plus Environment


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ABSTRACT:

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Accurate determination of polycyclic aromatic hydrocarbons (PAHs) in surface waters is

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necessary for protection of the environment from adverse effects that can occur at concentrations

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which require preconcentration to be detected. In this study, an effective solid phase extraction

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(SPE) method based on cetyltrimethylammonium bromide (CTAB)-coated Fe3O4 magnetic

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nanoparticles (MNPs) was developed for extraction of trace quantities of PAHs from natural

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waters. An enrichment factor of 800 was achieved within 5 min by use of 100 mg Fe3O4 MNPs

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and 50 mg CTAB. Compared with conventional Liquid-Liquid extraction (LLE), C18 SPE

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cartridge and some newly developed methods, the SPE to determine bioaccessible fraction was

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more convenient, efficient, time-saving and cost-effective. To evaluate the performance of this

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novel sorbent, 5 natural samples including rainwater, river waters, wastewater, tap water spiked

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with 15 PAHs were analyzed by use of ultra-performance, liquid chromatography (UPLC) with

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fluorescence detection (FLD). Limits of determination (LOD) of PAHs (logKow ≥ 4.46) ranged

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from 0.4 to 10.3 ng/L, with mean recoveries of 87.95 ± 16.16, 85.92 ± 10.19, 82.89 ± 5.25, 78.90

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± 9.90, and 59.23 ± 11.91% for rainwater, upstream and downstream river water, wastewater and

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tap water, respectively. However, the effect of dissolved organic matter (DOM) on recovery of

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PAHs varied among matrixes. Due to electrostatic adsorption and hydrophobicity, DOM promoted

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adsorption of Fe3O4 MNPs to PAHs from samples of water from the field. This result was different

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than the effect of DOM under laboratory conditions. Due to competitive adsorption with the site of

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action on the surface of Fe3O4 MNPs for CTAB, recoveries of PAHs were inversely proportional

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to concentrations of Ca2+ and Mg2+. This novel sorbent based on nano-materials was effective at

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removing PAHs at environmentally relevant concentrations from waters containing relevant 2


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concentrations of both naturally occurring organic matter and hardness metals.

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Polycyclic aromatic hydrocarbons (PAHs), of which there are thousands of possible

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variations in the environment, consist of two or more fused rings without heteroatoms, with some

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PAHs alkyl substituted.1,2 Most PAHs are released into the environment during leaks or spills

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during extraction, transport and refinery of petroleum hydrocarbons or during combustion of wood

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biofuels and fossil fuels such as coal and petroleum and other paths, such as cooking, burning of

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domestic wastes.2-6 Due to their ubiquitous presence, chemical stability, potential for

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bioaccumulation, and carcinogenic potential PAH in the environment have attracted attention

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globally and some have been listed as priority pollutants by the United States Environmental

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Protection Agency (USEPA).7-10

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Concentrations of PAHs in ground and surface waters, sediments and atmosphere are increasing

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due to activities of humans.11-13 There is a need to monitor PAHs, but they can occur at

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concentrations ranging from pg/L to ng/L, which, due to their propensity to be bioaccumulated,

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have potential to cause adverse effects, yet be less than the LOD of standard analytical techniques.

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Moreover, various environmental factors, such as chemical components, physical condition, can

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affect performances of pretreatment techniques.14-16

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concentrations of PAHs in environmental matrices, especially in water at environmentally and

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toxicologically relevant concentrations is needed. To achieve the required LOD, samples are

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concentrated and separated from environmental matrices by use of methods including liquid-liquid

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extraction (LLE), solid phase extraction (SPE) and solid phase micro-extraction (SPME) (Table

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S1). Each of these methods has advantages as well as limitations. Some are time-consuming and

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relatively expensive and result in large amounts of waste solvents.17-23 Use of a solid adsorbent

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based on C18 cartridges, to selectively pre-concentrate PAHs from environmental matrices uses

Accurate quantification of trace

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lesser amounts of organic solvents than does LLE. An alternative to these more traditional

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approaches is the use of adsorbents attached to nanoparticles that can be separated by used of a

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magnetic field. One such process uses Cetyltrimethylammonium bromide (CTAB) coated onto

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magnetic nanoparticles of iron oxide (Fe3O4) (Fe3O4-CTAB MNPs). This method has excellent

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capacity to separate PAH from environmental matrices, especially water, and is less expensive and

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quicker than the traditionally used methods that employ C18 disks or cartridges as the solid

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phase.18,23 The fact that larger volumes of water can be treated without breakthrough or

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interferences makes use of nanoparticles, such as nano-carbon, C-Fe3O4 and Ag-Fe3O4 an

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attractive approach to obtain lesser LODs for PAHs. Some of these solid phases might be

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unsuitable for treatment of large volumes of sample and could be time consuming to separate with

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sufficient recoveries.24,19 The superparamagnetic properties of magnetic nanoparticles (MNPs)

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contribute to their rapid magnetization and seperation from aqueous phases by use of external,

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magnetic fields. When coated with appropriate functional groups MNPs can enrich contaminants

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from large volumes of water.25 Additionally, advantages of MNPs including Fe3O4 and γ-Fe2O3 are

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their

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coprecipitation.26-28 While other adsorbents such as stir bars or artificial fibers were complicated to

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produce, Fe3O4-CTAB MNPs easily be synthesized. Because MNPs are magnetic, small particles,

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with large total surface area are effective for rapid and quantitative adsorption of PAHs and can

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easily be collected into an organic solvent by use of a magnetic field.29,30 Once separated from

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water the organics trapped on the surface can be extracted by use of an organic solvent. Thus,

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Fe3O4-CTAB MNPs have promise as a solid phase for extraction of PAHs in water.

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convenient,

biocompatibility

and

economical

synthesis

by

use

of

chemical

Enrichment of analytes by use of MNPs is improved by modification of surfaces of MNPs by 5



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addition of functional groups, such as coupling agents, surfactants, or noble metals.31 Ionic

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surfactants can attach homogeneously onto charged surfaces of MNPs by chemical self-assembly

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and due to their hydrophilic groups, form hemimicelles, mixed hemimicelles or admicelles.32 The

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mixed hemimicelles promote effective adsorption of PAHs by hydrophobic interaction with

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hydrocarbon moieties (Figure 1).33-35 MNPs as a substratum for sorbents, successfully avoid

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time-consuming, blocking problems during conventional SPE and relative to LLE, also reduces

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the amount of organic solvent used.

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Those PAHs, which have been deignated as priority pollutants by the USEPA, were

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quantified by use of ultra-performance liquid chromatography in tandem with fluoresence

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detection (UPLC-FLD), which can conviniently quantify all 15 PAHs within 30 min, while

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maintaining sufficient sensitivity, to attain LODs equivalent to the most commonly used analytical

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procedures. To our knowledge, this is the first report of utilization of MNPs for preconcentration

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of trace concentrations of PAHs from natural water.

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The objective of the present study was to develop a rapid, simple, cost-effective, SPE

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procedure using Fe3O4 MNPs coupled with UPLC-FLD for quantification of trace concentrations

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of the 15 priority PAHs, designated by USEPA, in water. Several key factors that could influence

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recoveries and accuracies and precision of determination of concentrations of PAHs isolated

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natural waters, such as pH, breakthrough volume, type and amounts of solvents used to elute

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analytes from the solid phase were determined. Effects of DOM, such as fulvic acid (FA) and

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humic acid (HA), and ions including Ca2+ and Mg2+ were investigated. Finally, the method was

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validated by application to five environmental waters.

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■ EXPERIMENTAL SECTION 6


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Reagents

and

Chemicals.

The

standard

solution

containing

Naphthalene

(Nap),

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Acenaphthylene (Ace), Fluorene (Flo), Phenanthrene (Phe), Anthracene (Ant), Fluoranthene (Fla),

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Pyrene (Pyr), Chrysene (Chr), Benzo(a)anthracene (Baa), Benzo(b)fluoranthene (Bbf),

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Benzo(k)fluoranthene

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Indeno(1,2,3-cd)pyrene (Icdp), Benzo(g,hi)perylene (BghiP) (2000 mg/L) was purchased from

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Sigma-Aldrich (St. Louis. MO, USA) and diluted to 1 mg/L as the stock solution for use in

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spiking waters. Samples were kept in the dark at 4 °C until used. Acetonitrile (ACN),

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Dichloromethane (DCM) and Acetone (DMK) were HPLC grade, and purchased form Fisher

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Scientific Corporation (Fair Lawn, NJ, USA). Acetic Acid (AcOH, A.R. grade) and Hydrochloric

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acid (A.R. grade) were purchased from Xilong Chemical Corporation (Guangdong, China).

(Bkf),

Benzo(a)pyrene

(Bap),

Dibenzo(a,h)anthracene

(DahA),

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Cetyltrimethylammonium bromide (CTAB, A.R. grade), (1-Hexadecy) pyridinium chloride

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monohydrate (CPC, A.R. grade), Ferric chloride (FeCl3·4H2O, A.R. grade), Ferrous Chloride

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(FeCl2·6H2O, A. R. grade), NaOH (sodium hydroxide, A.R. grade) were purchased from

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Sino-pharm Chemical Reagent Co., Ltd (Beijing, China). Fulvic Acid (Nordic Aquatic Fulvic Acid

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Reference 1R105F) and Humic Acid (Leonardite Humic Acid Standard 1S104H) were purchased

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from the International Humic Substances Society (Colorado, USA). Synthetic, experimental

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ultrapure water were made from Millipore Integral 5 water purification system (Merck, Germany).

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The Multi N/C3100 TOC (Analytikjena, Germany) analyzer was employed to determine the

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concentration of DOM in samples, and concentrations of Ca2+, Mg2+ in samples were determined

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by use of an Ion Chromatography System 1000 (DIONEX Co., USA).

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Collection of Samples. Samples of surface waters investigated included two samples of river

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water collected from the upstream stagnant pool (low-speed flow) and downstream reach 7



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(high-speed flow) of Qing River (Chinese: Qinghe), one sample of rainwater (August, 2014), one

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sample of wastewater collected from the Qing River wastewater treatment plant (Haidian district,

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Beijing), one sample of tap water sample from our laboratory (Chaoyang district, Beijing). The

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total volume of each sample was 10 L, and was collected with wide-mouth jars after cleaned with

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chromic acid and ultrapure water. Collected samples were immediately filtered through 0.45 µm

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glass fiber filter (combusted at 450 °C for 4 hours) combined with a filtration device to remove

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suspended solids and stored at 4 °C. All samples were analyzed within 5 days.

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SPE Procedure and Sample Analysis. Fe3O4 MNPs were synthesized by co-precipitation, by

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use of a previously described method.33 A 5 mL aliquant of Fe3O4 MNPs (20 mg/mL) and 10 mL

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of CTAB (5 mg/mL) were added to 800 mL of water, either a synthetic or natural sample, and pH

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adjusted to 10.0, and then sonicated for 1 min. After standing for 10 min on an Nd-Fe-B magnet,

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Fe3O4 MNPs coated with CTAB were isolated from solution, and the supernatant decanted.

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Pre-concentrated PAHs associated with CTAB-coated Fe3O4 MNPs were eluted with 2 mL ACN

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solution mixed with 5% acetic acid (AcOH) (v/v) for 5 times. The eluent containing PAHs was

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dried under a stream of nitrogen at 45 °C, and diluted to 1 mL with ACN.

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Ultra performance liquid chromatography coupled with fluorescence detection (UPLC-FLD,

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Waters, Massachusetts, USA) was employed to separate, identify and quantify individual PAHs. A

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CORTECS C18 column (100×2.1 mm I.D., with particle diameter of 1.6 µm, Waters,

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Massachusetts, USA) was used to separate 15 EPA PAHs. The mobile phases were ACN and

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ultrapure water at a flow rate of 0.4 mL/min, with an injection volume of 2 µL. The mobile phase

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was an ACN/water gradient program (45% ACN at start, 9.0 min hold, 15.0 min linear gradient to

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60%, 19.0 min linear gradient to 67%, 22.8 min linear gradient to 77%, 26.5 min linear gradient to 8


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100%, 28.0 min linear gradient to 45%). Excitation wavelengths were 221, 289, 252, 234, 265 and

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300 nm, and emission wavelengths were 337, 322, 377, 448, 390 and 412 nm for 0−5.5, 5.5−9.0,

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9.0−12.0, 12.0−15.0, 15.0−18.0, 18.0−28.0 minutes, respectively. Calculations for quantification of

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PAHs were accomplished by use of Waters Power 2.0 software. Limits of detection (LOD) for 15

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PAHs were determined as being 3 times the signal-noise ratio. PAH were quantified by use of an

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external standard curve with a linear working range of 0 to 400 ng/L. The analytical parameters of

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proposed method for PAHs are shown (Table 1).

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■ RESULTS AND DISCUSSION

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Characterization of Fe3O4-CTAB MNPs. Fe3O4 MNPs were characterized by use of

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transmission electronic microscopy (TEM) (Hitachi, Japan) at 80 kV. Particles were generally

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uniform with a diameter of approximately 10 nm (Figure 2). Hysteresis was not observed and the

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largest saturation magnetism of Fe3O4-CTAB MNPs was 58.7 emu/g,25 indicating their

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superparamagnetism excellence for rapid separation.

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Effect of Solution pH. pH is a key factor affecting adsorption of PAHs by Fe3O4-CTAB MNPs

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and in this study recoveries of PAHs were directly proportional to pH (Figure 3a), reaching a

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maximum at pH of approximate 10.0.

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Surfaces of Fe3O4 MNPs are negatively charged when the pH was greater than the pH where

169

the zeta potential of MNPs = 0, which is defined as the point of zero charge (PZC).25,36 Cationic

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surfactants can attach to surfaces of nanoparticles by strong electrostatic attraction to form

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hydrophobic hemimicelle, which creates a hydrophobic interaction with organic pollutants, such

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as PAHs (Figure 1). Octanol-water partition coefficients (Kow) of the 15 targeted PAHs were

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directly proportional to molecular mass (Table 1), such that adsorption of PAHs was inversely 9



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proportional to their solubilities in water. However, recoveries of Nap, Ace and Flo (logKow ≤

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4.46) were slightly less than those of other PAHs studied. This result might be due to their greater

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solubilities in water and greater volatility. For PAHs with logKow values greater than 4.46,

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recoveries of greater than 80% were observed.

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Effects of Amounts of Fe3O4 MNPs and Surfactant. CTAB was employed as the surface

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modifier at a ratio 1:2 (w/w) of CTAB and Fe3O4 MNPs, compared with CPC, and the detailed

180

information of this (Figure S1) and the effect of sample volume on recovery of PAHs (Figure S2)

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are provided in supporting information. In order to reduce consumption of adsorbents, the effect of

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amount of Fe3O4 MNPs and CTAB on recoveries of PAHs was determined. Recoveries of 15

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PAHs reached maxima separately as a function of amount of Fe3O4-CTAB MNPs added (Figure

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3b). However, PAHs with greater Kow reached maxima faster than those with lesser Kow. This

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result might be due to stronger affinities of Fe3O4-CTAB MNPs for chemicals with greater

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hydrophobicity than those with lesser Kow. The optimal amount of adsorbents used was the mean

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of the additive amounts of adsorbents for the greatest recovery of each PAH. Based on this

188

analysis, 100 mg Fe3O4 and 50 mg CTAB were chosen as the optimal amounts to use. Thus, in this

189

study, amounts of adsorbents were optimized to be more efficient and less wasteful than is

190

possible in studies using cartridges.

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Optimization of Standing Time. Duration of separation is a key factor for pretreatment

192

methods. Shorter paths of adsorption, which result in faster equilibrium are positive characteristics

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of nano-adsorbents. A duration of approximately 5 min was determined to be sufficient to obtain

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maximum enrichment of the 15 PAHs studied (Figure 3c). This was a clear advantage compared

195

with conventional pretreatment methods, such as LLE and C18 SPE cartridge, which had times to 10


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maxima of 72 − 1,080 and 125 − 333 min, respectively.17,18,37,38 Some other methods of

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preconcentration require a minimum of 30 min to reach their maxima. A detailed comparison is

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shown in Table S1.

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Optimization of Desorption Conditions. PAHs were eluted by mass action and destruction of

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hemimicelles with organic solvents. ACN and DMK were used separately to elute PAHs; 5%

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DCM was added to increase their capacity, and 5% AcOH was also added to destruct the mixed

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hemimicelles formed by CTAB under alkaline conditions to promote desorption of PAHs. ACN

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was better for eluting PAHs than was acetone (Figure 3d). This might have been due to greater

204

solubility of CTAB in ACN than acetone. In this study, 10 mL (2 mL for 5 times) ACN was

205

sufficient to ensure sufficient recoveries of PAHs.

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Effects of Fulvic Acid and Humic Acid. DOM is complex and comprises a variety of organic

207

substances including FA, HA, carbohydrates, sugars, amino acids, proteins, inorganic ions, among

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others.39 Since FA and HA are the main components of DOM in the environment,40 and carry a

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variety of functional groups, they can interfere adsorption of PAHs by Fe3O4-CTAB MNPs,

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mainly through electrostatic interaction or hydrophobic interaction due to their different

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concentrations.41

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Concentrations of total organic carbon (TOC) in aquatic environments ranges for 20−100

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mg/L, depending on soil types in the watershed, climate, and hydrologic conditions,39 thus

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concentrations of FA and HA considered in this study ranged from 0 to 120 mg/L, and their effects

215

on recoveries of PAHs were assessed separately. FA and HA had similar effects on recoveries of

216

PAHs by Fe3O4-CTAB MNPs (Figure 4a and b). The effect of DOM on recovery of PAHs could

217

be divided into three stages: the recovery of PAHs initially declined with the addition of FA for 0− 11



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40 mg/L (HA for 0−50 mg/L), and then increased with the addition of FA for 40 − 80 mg/L (HA

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for 50−100 mg/L), and slightly decreased at the concentration of FA for 80 mg/L (HA for 100

220

mg/L). The stages observed: 1) Competitive adsorption of DOM with Fe3O4 MNPs to bind CTAB

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and PAHs, resulted in lesser recoveries of PAHs. DOM is generally electronegative at pH 10.0,

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because there are more negative charged functional groups than positive groups on DOM.42-44

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However, the majority of added DOM partitioned into the aqueous phase, adsorbed CTAB to form

224

hemimicelle structure by electrostatic interactions, and had a competition with Fe3O4-CTAB

225

MNPs for adsorbing PAHs by the hydrophobic effect;36, 43 and meanwhile, less of DOM adsorbed

226

on the surface of Fe3O4-CTAB MNPs, and competed with PAHs for adsorption sites.45-47 The

227

above both effects of DOM resulted in the decrease of recoveries of PAHs by Fe3O4-CTAB MNP.

228

Thus, PAHs adsorbed by DOM or DOM-CTAB would not have been extracted by Fe3O4 MNPs

229

due to the electrostatic repulsion between DOM or DOM-CTAB and MNPs (Figure 5a and b).

230

These combinations of pH-dependent phenomena resulted in recoveries of PAHs being inversely

231

proportional to concentration of DOM until a concentration of 40 mg/L for FA and 50 mg/L for

232

HA. 2) Recoveries of PAHs were increasing until the concentration of FA reached 80 mg/L or for

233

HA 100 mg/L. This phenomenon has been less reported. And at this stage, the newly added FA

234

and HA also adsorbed the CTAB and PAHs, which might reduce electrostatic repulsion between

235

the DOM complex and Fe3O4-CTAB MNPs. As a result, DOM complexes would be adsorbed onto

236

surfaces of Fe3O4-CTAB MNPs, and some polymers such as flocculation,48,49 were gradually

237

formed with addition of FA and HA due to electrostatic and hydrophobic interactions. It has been

238

reported removal of DOM from water with bentonite and benzyltrimethylammonium bromide by

239

flocculation reaction (Figure 5c).50 When more than 80 mg/L FA and 100 mg/L HA was added to 12


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the solution, newly added DOM would also compete with previously added DOM and

241

Fe3O4-CTAB MNPs for adsorbing PAHs. One possible mechanism is that Fe3O4-CTAB MNPs and

242

DOM or DOM-CTAB would both be more electronegative, because the competitive adsorption of

243

the new added DOM to CTAB and PAHs from previously formed polymers. Therefore,

244

electrostatic repulsion between DOM complexes and Fe3O4-CTAB MNPs was recovered due to

245

electrostatic repulsion regenerated by their electronegativity, which decreased adsorption of PAHs

246

by Fe3O4-CTAB MNPs (Figure 5d).

247

Method Parameters. Calibration curves were run for 15 PAH in the range of 0−400 ng/L.

248

Coefficients of determination (r2) for PAHs (logKow ≥ 4.46) were all greater than 0.99, and LODs

249

were calculated by using 3 times the signal-to-noise, and ranges from 0.4 to 10.3 ng/L, which

250

indicated suitability of MNPs for preconcentration of neutral, hydrophobic organic pollutants,

251

such as PAHs. However, lesser recoveries of Nap, Ace and Flo were likely due to their greater

252

volatilities and solubilities in water. Therefore, coefficients of determination (r2) for Ace and Flo

253

were 0.78 and 0.88, but an adequate standard curve could not be obtained for Nap.

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Analyses of Environmental Water Samples. Reproducibility of recoveries of PAHs by

255

Fe3O4-CTAB MNPs was investigated by spiking known amounts of the standard mixture of PAHs

256

into samples of rainwater, two samples of river water, wastewater, and tap water. Figure 6 shows

257

the chromatograms of PAHs in the water samples of Qing river by using UPLC-FLD. Effects of

258

physical-chemical factors were also investigated. Total concentrations of 15 PAHs in the samples

259

for rainwater, upstream and downstream river water, wastewater and tap water were 924.3 ± 80.71,

260

1206.99 ± 89.20, 1669.91 ± 148.65, 2232.47 ± 38.12, 305.54 ± 25.07 ng/L, respectively.

261

Recoveries of PAHs were about 90, 80, 70 and 60% in rainwater, both samples of river water, 13



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262

wastewater and tap water, respectively (Table 2).

263

Concentrations of Ca2+, Mg2+ and DOM in natural water affected performance of

264

Fe3O4-CTAB MNPs on extraction of PAHs. There could be two aspects of their interactions: 1)

265

Fe3O4 MNPs were electronegative at pH 10.0, and a competitive adsorption of metal ions with

266

CTAB on surfaces of Fe3O4 MNPs, prevented formation of mixed hemimicelles, and resulted in

267

poorer recoveries of PAHs.51,52 2) due to strong complexation between Ca2+, and Mg2+ and some

268

functional groups (carboxyl, phenolic hydroxyl) of DOM,42, 46-48 which was also due in part to

269

lesser adsorption of CTAB to DOM. Thus, presence of DOM would indirectly reduce the effect of

270

metal irons on adsorption activity of MNPs to PAHs, as well as increasing development of mixed

271

hemimicelles, which increased adsorption of PAHs by Fe3O4-CTAB MNPs.53,54

272

Concentrations of TOC in five environmental waters are 23.22 ± 0.62, 8.41 ± 0.32 and 3.58 ±

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0.44 mg/L for wastewater and upstream and downstream river water, respectively with no DOC

274

detected in tap water or rain water (Table S2). Recoveries of PAHs from rain water were greater

275

due to lesser concentrations of Ca2+, Mg2+ and DOM. The relatively greater concentrations of Ca2+

276

and Mg2+ in tap water reduced adsorption of PAHs due to electrostatic binding to Fe3O4 MNPs,

277

which are competitive for CTAB, and could prevent formation of mixed hemimicelles.55 DOM in

278

river water and waste water reduced effects of Ca2+ and Mg2+ on performance of Fe3O4 MNPs due

279

to complexation of the metal ions, which resulted in greater recoveries of PAHs.56 Some polymer

280

micro-molecules (PAHs-DOM-CTAB-Fe3O4) might have formed due to the hydrophobic

281

interaction of DOM, CTAB, and Fe3O4 MNPs.50 Therefore, Fe3O4-CTAB MNPs performed better

282

in extracting stable hydrophobic organic pollutions. Because of the negative and positive effects of

283

both DOM and metal ions, it is suggested that the most accurate and reproducible method 14


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284

employing Fe3O4-CTAB MNPs would be the use of internal standards using mass-labeled PAHs.

285

■ CONCLUSIONS

286

The Fe3O4-CTAB MNPs, used in the present study, had several advantages for extraction of

287

PAHs from water. First, their relatively large specific surface area provided more adsorption sites

288

for PAHs, and their superparamagnetism also benefited rapid separation. Second, separation of

289

PAHs was completed within 5 min, and the preconcentration process was convenient, which

290

greatly shortened the duration required for maximal extraction. Third, relatively small amounts of

291

organic solvents were need, which avoided waste of solvents. Fourth, the Fe3O4-CTAB MNPs can

292

easily be synthesized with several low-cost chemicals, which might be more suitable to

293

industrialization for the determination of trace organic pollutants. Last, the lesser biotoxicity of

294

Fe3O4 MNPs and CTAB might potentially reduce pollution of the environment, compared with

295

other nano-materials. In conclusion, Fe3O4-CTAB MNPs as a solid adsorbent combined with

296

UPLC-FLD presented excellent performance in analyzing trace PAHs in water.

297

■ ACKNOWLEDGEMENTS

298

The research was supported by the National Natural Science Foundation of China

299

(No41222026, 41130743 and 21007063). Prof. Giesy was supported by the program of 2012

300

"High Level Foreign Experts" (#GDT20143200016) funded by the State Administration of

301

Foreign Experts Affairs, the P.R. China to Nanjing University and the Einstein Professor Program

302

of the Chinese Academy of Sciences. He was also supported by the Canada Research Chair

303

program.

304

■ SUPPORTING INFORMATION AVAILABLE

305

Selection and additive amount of surfactants, selection of sample volume and collected parameters 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

306

of preconcentration techniques for PAHs from water, Table S1 and S2, Figure S1, S2 and S3. This

307

information is available free of charge via the Internet at http://pubs.acs.org.

16


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308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351

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(35) Du, J.; Jing, C. J. Colloid Interface Sci. 2011, 358, 54−61. (36) Hu, J. D.; Zevi, Y.; Kou, X. M.; Xiao, J.; Wang, X. J.; Jin, Y. Sci. Total Environ. 2010, 408, 3477−3489. (37) Hawthorne, S. B.; Grabanski, C. B.; Martin, E.; Miller, D. J. J. Chromatogr. A 2000, 892, 421−433. (38) Chen, Y.; Zhu, L.; Zhou, R. J. Hazard. Mater. 2007, 141, 148−155. (39) Wu, F. C.; Xing, B. S. In Natural organic matter and its significance in the environment; Xie, H. Y., Luo, J., Eds.; Beijing Science Press: Beijing, 2009; pp 20−21. (40) Selberg, A.; Viik, M.; Ehapalu, K.; Tenno, T. J. Hyrdrol. 2011, 400, 274−280. (41) Cho, H. H.; Choi, J.; Goltz, M. N.; Park, J. W. J. Environ. Qual. 2002, 31, 275−280. (42) Avena, M. J.; Koopal, L. K. Environ. Sci. Technol. 1998, 32, 2572−2577. (43) Grybos, M.; Davranche, M.; Gruau, G.; Petitjean, P.; Pédrot, M. Geoderma 2009, 154, 13−19. (44) Zhao, X.; Li, J.; Shi, Y.; Cai, Y.; Mou, S.; Jiang, G. J. Chromatogr. A 2007, 1154, 52−59. (45) Li, J.; Werth, C. J. Environ. Sci. Technol. 2001, 35, 568−574. (46) Chin, Y. P.; Weber, W. J.; Eadie, B. J. Environ. Sci. Technol. 1990, 24, 837−842. (47) Moon, J. W.; Goltz, M. N.; Ahn, K. H.; Park, J. W. J. Contam. Hydrol. 2003, 60, 307−326. (48) Kretzschmar, R.; Sticher, H.; Hesterberg, D. Soil Sci. Soc. Am. J. 1997, 61, 101−108. (49) Kim, E. K.; Walker, H. W. Colloid Surf. A−Physicochem. Eng. Asp. 2001, 194, 123−131. (50) Shen, Y. H. Environ. Technol. 2002, 23, 553−560. (51) Beckett, R.; Le, N. P. Colloids Surf. 1990, 44, 35−49. (52) Pan, B.; Qiu, M.; Wu, M.; Zhang, D.; Peng, H.; Wu, D.; Xing, B. Environ. Pollut. 2012, 161, 76−82. (53) Schlautman, M. A.; Morgan, J. J. Environ. Sci. Technol. 1993, 27, 961−969. (54) Haftka, J. H.; Govers, H. J.; Parsons, J. Environ. Sci. Pollut. Res. 2010, 17, 1070−1079. (55) Hayes, K. F.; Leckie, J. O. J. Colloid Interf. Sci. 1987, 115, 564−572. (56) Riedel, T.; Biester, H.; Dittmar, T. Environ. Sci. Technol. 2012, 46, 4419−4426. (57) Huckins, J. N.; Petty, J. D.; Orazio, C. E.; Lebo, J. A.; Clark, R. C.; Gibson, V. L.; Gala, W. R.; Echols, K. R. Environ. Sci. Technol. 1999, 33, 3918−3923.

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381 382

Figure 1. Schematic representation of mechanism of adsorption of PAHs by Fe3O4-CTAB MNPs.

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

383 384

Figure 2. Transmission electron microscopy (TEM) image of Fe3O4 MNPs.

20


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Page 21 of 27

a

120

Recovery (%)

80 60 40 20 0

5

6

7

8

c

9

10

11

60 40 20

20

30

100 80 60 40 20 0

13

40

50

60

70

Nap Ace Flo Phe Ant Fla Pyr Chr Baa Bbf Bkf Bap DahA IcdP BghiP

20 40 60 80 100 120 140 160 180 200 220 240

mg Fe3O4 MNPs added as a ratio of 2:1 to CTAB


80

10

12

120

pH

100

0

b


100

Recovery (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


d

100 80 60 40 20

80

Time (min)

0


95% ACN 90% ACN 95% DMK 90% DMK 5% AcOH 5% AcOH 5% AcOH 5% AcOH 5% DCM 5% DCM

Different eluents

385 386

Figure 3. Recoveries of PAHs as functions of Fe3O4 MNPs as pH (a), ratio of 2:1 to CTAB (b), standing time (c), and 4 kinds of eluents (d) in batch mode. Sample

387

volume: 800 mL, Volume of ACN: 10 mL. (a) (c) and (d) 100 mg of Fe3O4 MNPs, surfactant: 50 mg CTAB, (b) pH 10.0.

21



a Nap Ace Flo Phe Ant Fla Pyr Chr Baa Bbf Bkf Bap DahA IcdP BghiP

100 80 60 40 20 0

0

20

40 60 80 Fulvic acid (mg/L)

b

120


100 80 Recovery (%)

120

Recovery (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 22 of 27

60 40 20 0

100

0

20

40 60 80 100 Humic acid (mg/L)

120

140

388 389

Figure 4. Recoveries of PAHs as functions of FA (a) and HA (b) in batch mode. Amount of metal oxide: 100 mg of Fe3O4 MNPs. Surfactant: 50 mg CTAB. pH: 10.0,

390

sample volume: 800 mL. Volume of ACN: 10 mL.

22


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48


391 392

Figure 5. Schematic representation of interactions among CTAB, DOM, PAHs, Fe3O4 MNPs. (a) from adsorption of CTAB onto Fe3O4 MNPs; (b) from adsorption of

393

CTAB onto Fe3O4 MNPs and less DOM separately; (c) formed from DOM complex and Fe3O4 MNPs by the bridging effect of CTAB; (d) decrease recovery of PAHs

394

by sorption supersaturation of Fe3O4 MNPs to more DOM additives. 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

395 396

Figure 6. Solid-phase extraction/UPLC-FLD chromatograms. (a) Qing river water sample; (b) Qing river water sample spiked with 60 ng/L of PAHs.

24


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397


Table 1. Analytical parameters of the proposed method. PAHs Naphthalene

Acenaphthene Fluorene Phenanthrene

Nap Ace Flo Phe

(g/m3) 30.2 3.93 1.9 1.18

the range of

Slope ± SD

correlation

LODb

RSD (%)

concentration (ng/L)

[mV·L/ng]

coefficient (r2)

(ng/L)

(n=3)

a

LogKow 3.45 4.22

0.1−400

4.38

0.1−400

4.46

0.1−400

-

20.6

-

3

0.782

0.7

18.0

4

0.888

3.9

10.2

3

0.992

10.3

3.9

4

-

0.1−400

(0.96±0.21)×10

(1.91±0.19)×10 (7.84±0.06)×10

Anthracene

Ant

0.076

4.54

0.1−400

(1.25±0.03)×10

0.999

0.5

6.9

Fluoranthene

Fla

0.26

5.2

0.1−400

(4.50±0.04)×103

1.000

3.5

4.4

0.1−400

3

1.000

6.4

2.4

4

0.998

1.0

2.4

4

Pyrene Chrysene

Pyr Chr

0.135 0.0019

5.3 5.61

0.1−400

(1.63±0.02)×10 (5.09±0.12)×10

Benzo[b]fluoranthene

Bbf

0.014

5.78

0.1−400

(4.49±0.15)×10

0.993

0.4

5.2

Benzo(a)anthracene

Baa

0.011

5.91

0.1−400

(3.07±0.12)×104

0.996

1.7

4.3

Benzo(k)fluoranthene

Bkf

0.008

6.2

0.1−400

(3.58±0.11)×105

0.995

1.2

7.5

0.1−400

5

0.995

1.7

6.0

4

0.990

3.3

4.2

5

Benzo[a]pyrene Dibenz[a,h]anthracene Indeno[1,2,3-cd]pyrene Benzo[ghi]perylene 398

abrreviation

water solubility

a

Bap DahA

0.0038 0.0005

6.35 6.75

0.1−400

(2.09±0.11)×10

(9.63±0.20)×10

IcdP

0.0005

6.51

0.1−400

(1.18±0.06)×10

0.996

3.5

4.3

BghiP

0.0003

6.9

0.1−400

(1.20±0.02)×103

0.999

2.3

8.2

57 b

water solubilities and logKow of 15 PAHs are quoted from Huckins et al.

the detection limits were calculated by using S/N=3.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

399

Table 2. Results of determination and recoveries of natural water samples spiked with 60 ng/L of PAHs. samples

a

rainwater

downstream water

upstream water

wastewater

tap water

PAHs

detecteda (ng/L)

recoveryb (%)

detecteda (ng/L)

recoveryb (%)

detecteda (ng/L)

recoveryb (%)

detecteda (ng/L)

recoveryb (%)

detecteda (ng/L)

recoveryb(%)

Nap

97.12±6.24

45.99±24.32

181.94±29.36

52.86±19.91

395.88±12.96

86.34±21.25

360.00±13.74

62.64±16.95

128.6±14.00

19.40±1.71

Ace

270.47±37.39

63.53±24.48

492.39±17.28

91.35±24.07

558.42±71.68

79.69±18.31

1177.08±19.55

67.06±15.25

65.01±3.21

47.71±3.55

Flo

329.57±22.75

85.22±16.11

319.28±27.21

94.00±21.39

421.18±49.12

86.71±13.50

395.01±2.39

80.79±11.44

69.75±4.46

56.89±8.04

Phe

168.75±6.02

80.04±7.24

92.33±10.80

89.67±12.92

167.82±8.70

84.60±10.20

178.39±0.96

95.19±5.05

30.41±2.19

63.60±0.19

Ant

18.25±0.98

82.78±6.35

13.63±0.50

96.27±6.40

11.09±0.50

96.11±7.32

9.16±0.16

72.52±1.05

2.40±0.12

66.55±1.91

Fla

12.54±0.75

87.44±9.23

10.97±0.83

93.36±3.03

18.16±2.24

87.74±7.07

18.26±0.15

85.47±3.35

2.69±0.17

63.65±0.04

Pyr

8.77±1.11

85.10±8.36

14.10±0.69

83.33±4.21

12.09±2.57

82.46±1.66

10.31±0.14

88.25±2.45

0.06±0.08

63.25±6.06

Chr

2.81±0.21

92.44±9.83

8.69±0.16

86.82±1.61

7.81±0.04

81.06±1.74

7.75±0.02

77.83±3.59

0.75±0.05

63.50±3.62

Baa

1.87±0.21

94.80±11.02

10.33±0.19

84.64±0.19

12.31±0.09

82.21±3.13

12.10±0.08

76.89±3.24

1.15±0.03

62.94±2.11

Bbf

2.73±0.26

96.86±10.53

10.69±0.26

85.55±0.80

9.37±0.06

78.87±1.12

9.61±0.02

69.88±3.30

0.15±0.01

63.95±2.58

Bkf

1.44±0.31

97.40±10.87

9.26±0.13

85.68±14.52

10.37±0.07

77.80±1.98

10.20±0.01

75.21±3.46

0.48±0.01

62.34±2.97

Bap

0.77±0.45

102.99±3.62

13.17±0.19

79.06±2.77

16.83±0.11

74.15±1.53

16.66±0.01

72.92±2.87

0.41±0.00

61.02±5.34

DahA

1.54±0.83

101.53±12.13

10.01±0.40

89.93±4.02

12.05±0.09

80.76±1.90

11.98±0.03

82.17±4.32

0.47±0.23

65.60±2.89

IcdP

4.25±2.43

92.04±12.28

13.22±0.44

89.97±0.58

13.23±0.33

79.22±2.49

12.64±0.57

78.29±3.79

1.98±0.29

63.57±3.26

BghiP

3.42±0.77

111.04±8.24

6.98±0.76

86.38±4.86

3.30±0.09

85.66±1.76

3.32±0.29

98.42±9.80

1.23±0.22

64.50±2.21

305.54±25.07

59.23±11.91c

total

400

Page 26 of 27

924.3±80.71

87.95 ±16.16

c

1206.99±89.22

c

82.89±5.25

1669.91±148.65

85.92±10.19

c

2232.47±38.12

Mean of three determinations. b Standard deviation for three determinations. c mean recovery of 15 PAHs.

26


c

82.89±5.25

Page 27 of 27

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401

402


Table of Contents (TOC) graphic:

for TOC only.

27


Cetyltrimethylammonium Bromide-Coated Fe3O4 Magnetic

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