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Journal of Chromatography A, 1216 (2009) 6155–6161

Contents lists available at ScienceDirect

Journal of Chromatography A

journa l homepage: www.e lsev ier .com/ locate /chroma

pplication of hollow fiber liquid-phase microextraction in identification ofil spill sources

un Li a, Yongqiang Xiong a,∗, Jidun Fang b, Lifang Wang b, Qianyong Liang a

State Key Laboratory of Organic Geochemistry (SKLOG), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, ChinaState Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

r t i c l e i n f o

rticle history:eceived 6 April 2009eceived in revised form 20 June 2009ccepted 26 June 2009vailable online 1 July 2009

a b s t r a c t

In this study, hollow fiber based liquid-phase microextraction (HF-LPME), coupled with GC, GC–MS andGC–IRMS detections, was employed to determine petroleum hydrocarbons in spilled oils. According tothe results, the HF-LPME method collected more low-molecular weight components, such as C7–C11

n-alkanes, naphthalene, and phenanthrene, than those collected in conventional liquid–liquid extrac-tion (LLE). The results also showed that this method had no remarkable effect on the distributions ofhigh-molecular weight compounds such as >C18 n-alkanes, C1–C3 phenanthrene, and hopanes. Also, the

eywords:ample preparationollow fiberiquid-phase microextractionil spilleathering

as chromatography–isotope ratio mass

carbon isotopic compositions of individual n-alkanes in the two preparation processes were identical.Accordingly, HF-LPME, as a simple, fast, and inexpensive sample preparation technique, could become apromising method for the identification of oil spill sources.

© 2009 Elsevier B.V. All rights reserved.

pectrometry

. Introduction

China has become the world’s fifth largest oil producer and theecond largest oil consumer. Oil spills and other petroleum-relatedontaminations frequently occur in various water bodies (rivers,akes, coastal waterways and groundwater) and soils, posing poten-ial risks to the natural environment and human health. The exactdentification of oil spill sources can provide forensic evidence forhe investigation and handling of oil spill accidents [1,2]. How-ver, the compositional complexity of crude oils and their refinedroducts, as well as alterations by weathering (exposure of oil tohysical, chemical, and biological processes), could influence theeliability of the results.

In recent years, various detection techniques, diagnostic ratios,nd data processing methods have been developed for determina-ion of oil spills’ sources. In contrast, the treatment of samples prioro analysis has been a neglected but critical issue. Faster treatmentnd less influence on the analysis are necessary. In this study, more

ttention is paid to advancing the methods of sample preparationn order to simplify pretreatment and shorten the analytical time.

For extraction and enrichment of petroleum hydrocarbons inater, the conventional liquid–liquid extraction (LLE) method is not

∗ Corresponding author. Tel.: +86 20 85290744; fax: +86 20 85290706.E-mail address: xiongyq@gig.ac.cn (Y. Xiong).

021-9673/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.chroma.2009.06.069

only tedious, time-consuming, and labor-intensive, but also lim-ited as solvent evaporation concentrates the sample and may resultin the loss of some analytes, especially for low-molecular weightcomponents.

As a novel, simple, and solvent-free technique that incorpo-rates extraction, concentration, and injection into a single step,solid-phase microextraction (SPME) has been successfully intro-duced for determining diesel spilled samples [3,4]. In the past fewyears, liquid-phase microextraction (LPME) has been developed asanother rapid, simple, inexpensive, and environmentally friendlysample preparation technique [5–7]. Single drop microextraction(SDME) is the simplest operational mode of the LPME technique,in which a single liquid drop is used as the collection phase thatreplaces the coated fiber. The analytes are extracted by a micro-drop of organic solvent (about 1–3 �L) suspended from the tip of aconventional micro-syringe needle and exposed in the headspaceof a stirred sample solution (HS-SDME) [8], or immersed into thestirred aqueous sample (direct SDME) [9,10], then injected directlyinto a gas chromatography system. However, the disadvantage ofSDME is that the stability of the suspended organic drop is easilyaffected by temperature, stirring rate, air bubbles, etc. [11–14].

To overcome the solvent instability, a hollow fiber based liquid-phase microextraction method (HF-LPME) has been developed[15–17]. Since the organic phase is protected by the hollow fiber,the stability is greatly improved, and higher stirring rates can beused to reduce the equilibrium and extraction times. As a result,

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etter extraction efficiency and sensitivity are achieved [18–20].oreover, the hollow fiber can prevent the interference of complex

ample matrices [11,21,22]. Unlike the fibers of SPME, hollow fibersan be renewed for each extraction, making this an elegant methodo overcome some of the drawbacks of SPME (e.g., fiber fragility,imited availability of fiber coatings, expensive devices, and carry-ver between analyses). Therefore, HF-LPME is an attractive samplereparation method for oil spill identification.

To the best of our knowledge, no reports exist about the applica-ion of HF-LPME to an oil spill investigation. To prove the feasibilityf this method in the source identification of an oil spill, we con-ucted a laboratory weathering simulating experiment on oil spills.eathered samples were pretreated using the HF-LPME technique.

he extracts were then determined by GC, GC–MS, and GC–IRMS.inally, the results were compared with those we obtained from ourrevious weathering experiment several months ago [23], in whichhe samples were treated by the conventional LLE method.

. Experimental

.1. Weather simulating experiment

As described [23], a group of simplified weathering simulationxperiments were performed on the same crude oil from an off-hore oil production platform in the South China Sea. In order tose HF-LPME, each experiment was finished in a 4 mL screw-necklass vial replacing in a beaker. About 5 mg of crude oil was droppedn each surface of distilled water contained in a series of vials,nd the volume of each oil–water mixture was about 3.5 mL. Thenhe mixtures were left uncapped on a windowsill to evaporate atoom temperature. The vials were sealed in turn after 0.1, 1, 2, 5,4, 48, and 72 h. Residual oils in each vial were pretreated usinghe HF-LPME method. Afterwards, the extracts were measured byC, GC–MS, and GC–IRMS. The original crude oil was dissolved in-hexane, and then analyzed in parallel.

.2. HF-LPME

In this study, hollow fiber based LPME procedures were basedn polyvinylidene difluoride obtained from Motianmo Membraneechnology Ltd. (Tianjin, China). The inner diameter of the fiberas 500 �m, the wall thickness was 150 �m, and the pore size was

.2 �m. The length of 2 cm with an acceptor phase volume of about�L was used in each extraction process.

At the beginning, the hollow fiber membrane was sonicatedn dichloromethane three times, each time for about 5 min toemove any contaminant. The fibers were removed to a ventilationabinet to air dry. The HF-LPME device was adopted from Pedersen-jergaard and Rasmussen [14]. A 10 �L micro-syringe was used to

ntroduce the acceptor phase and support the hollow fiber. Then�L of n-hexane was withdrawn into the syringe, followed by�L of distilled water. The tip of the micro-syringe needle was

nserted into the hollow fiber, which was then immersed into n-exane for 5 min. After solvent impregnation, the fiber was rapidly

mmersed into a vial containing the aqueous sample. Next, the 3 �Lf water in the micro-syringe was injected carefully into the hollowber, thus removing n-hexane from the inside. Then, the syringe’slunger was further depressed and the remaining 4 �L of n-hexane

n the syringe was injected into the hollow fiber as the acceptor

hase. A magnetic stirrer (700 rpm) was used for agitating the sam-le, and a microextraction procedure began. After extracting for0 min at room temperature, n-hexane was withdrawn into theicro-syringe and injected into a 4 mL sample vial. The extractsere diluted by n-hexane, and then analyzed by GC, GC–MS andC–IRMS.

216 (2009) 6155–6161

2.3. Gas chromatography (GC)

GC analyses were conducted using a Finngan Trace GC sys-tem (Thermo electron corporation, Italy), fitted with a HP-5 fusedsilica capillary column (50 m × 0.32 mm × 0.25 �m, Agilent Tech-nologies, U.S.A.), and a flame ionization detection (FID). Nitrogen(≥99.999%) was used as the carrier gas, at a flow of 1.5 mL/min. TheGC oven temperature was held isothermally for 5 min at 40 ◦C, pro-grammed to sequentially step from 40 to 290 ◦C at 5 ◦C min−1, andheld isothermally for 40 min at 290 ◦C. Quantitations of n-alkanesand isoprenoids were achieved by integration of the peak areas.

2.4. Gas chromatography–mass spectrometry (GC–MS)

GC–MS analyses were performed on a Micromass Platform IIinstrument (UK) equipped with a HP-5 fused silica capillary column(50 m × 0.32 mm × 0.25 �m, Agilent Technologies, U.S.A.). Helium(≥99.999%) was used as carrier gas, at a flow of 1.0 mL/min. Theoven temperature was programmed at 60 ◦C for 2 min, increased to290 ◦C at 4 ◦C min−1, and held isothermally for 40 min at 290 ◦C. Forthe scanning of terpane and sterane compounds, the MS operatedin a single ion monitoring (SIM) mode. The ions monitored werem/z 191 for terpanes and m/z 217 and 218 for steranes. To obtainspectral data and identification of the polycyclic aromatic hydro-carbons (PAHs), the MS operated in a selected ion resolution (SIR)mode. The ions monitored were m/z 128, 142, 156, 170, and 184for naphthalene and alkyl-naphthalenes and m/z 178, 192, 206, and220 for phenanthrene and alkylphenanthrenes.

2.5. Gas chromatography–isotope ratio mass spectrometry(GC–IRMS)

GC–IRMS analyses were performed on a VG Isoprime instrument(GV Instruments Ltd., UK). Separations were made using a HP-5capillary column (50 m × 0.32 mm × 0.25 �m, Agilent Technologies,U.S.A.) with helium as the carrier gas, at a flow of 1.5 mL/min. The GCcondition was as follows: initial oven temperature 60 ◦C for 2 min,increased to 185 ◦C at a rate of 3 ◦C min−1 and a second ramp to295 ◦C at a rate of 5 ◦C min−1, then held isothermally for 30 min. Thecombustion furnace was run at 880 ◦C. The carbon isotope ratios forindividual alkanes were calculated using CO2 as a reference gas thatwas automatically introduced into the IRMS at the beginning andend of each analysis, and the data is reported in per mil (‰) relativeto the VPDB standard. A standard mixture of n-alkanes (C12, C14, C16,C18, C20, C22, C25, C28, C30, and C32, provided by Schimmelmann A.of Indiana University, website: http://mypage.iu.edu/∼aschimme)with a known isotopic composition was used daily to monitor theaccuracy of measurements with the GC–IRMS system. Replicateanalysis of this mixture showed that the standard deviation for eachcompound was less than 0.3‰. Reported isotopic data representedthe arithmetic means of at least two repeated analyses, and therepeatability was less than 0.5‰.

3. Results and discussion

Diagnostic ratios based on n-alkanes, isoprenoids, polycyclicaromatic hydrocarbons, and terpane and sterane biomarkers aretypically used for characterizing the chemical compositions ofspilled oils and their suspected sources. Table 1 lists some common

diagnostic ratios of samples from the two simulating experiments.Samples were derived from the simulating experiment in this studyand were prepared using the HF-LPME method. Correspondingly,LLE results were from a similar weathering simulation experimentperformed months ago, and used the conventional LLE samplepreparation method [23].

Y.Lietal./J.Chrom

atogr.A1216 (2009) 6155–6161

6157

Table 1Some common parameters used in the identification of oil spill sources.

Method Ratio/parameter* Oil 0.1 h 1 h 2 h 5 h 24 h 48 h 72 h Mean SD %RSD

HF-LPMEPr/n-C17

0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.26 0.00 0.97LLE 0.47 0.45 0.44 0.46 0.47 0.46 0.45 0.44 0.46 0.01 2.25

HF-LPMEPh/n-C18

0.10 0.10 0.11 0.10 0.10 0.10 0.10 0.10 0.10 0.00 2.77LLE 0.24 0.18 0.18 0.19 0.23 0.20 0.21 0.21 0.20 0.02 10.5

HF-LPMEPh/Pr

0.32 0.31 0.34 0.32 0.31 0.30 0.32 0.31 0.32 0.01 3.46LLE 0.46 0.35 0.35 0.36 0.43 0.43 0.45 0.48 0.41 0.05 12.7

HF-LPMEDMNR

3.83 3.17 2.32 3.82 4.54 3.17 3.09 3.62 3.45 0.66 19.2LLE 1.71 2.02 1.96 1.94 1.69 1.91 1.27 2.04 1.82 0.26 14.1

HF-LPMETMNR

1.08 1.17 0.90 1.23 1.05 1.16 1.04 1.21 1.11 0.11 9.89LLE 1.02 1.13 1.12 1.11 1.14 1.07 1.43 0.71 1.09 0.20 18.1

HF-LPMETeMNR

0.59 0.58 0.59 0.57 0.53 0.59 0.61 0.57 0.58 0.02 4.24LLE 0.56 0.57 0.56 0.58 0.56 0.47 0.47 0.46 0.53 0.05 9.87

HF-LPMEMPR

1.42 1.32 1.69 1.44 1.07 1.22 1.12 1.32 1.32 0.20 15.0LLE 1.15 1.23 1.25 1.22 1.22 1.10 1.11 1.16 1.18 0.06 4.93

HF-LPMEMPI-1

0.85 0.79 0.78 0.82 0.69 0.78 0.69 0.80 0.78 0.06 7.45LLE 0.68 0.66 0.69 0.67 0.70 0.81 0.84 0.94 0.75 0.10 13.6

HF-LPMEMPI-2

1.03 0.93 0.99 1.07 0.87 0.93 0.91 0.95 0.96 0.07 6.83LLE 0.91 0.94 0.95 0.96 0.95 0.85 0.86 0.88 0.91 0.04 4.57

HF-LPMEPAI

2.50 2.48 2.23 2.18 2.10 2.49 1.96 2.48 2.30 0.21 9.29LLE 1.90 1.71 1.83 1.71 1.92 3.24 3.45 4.56 2.54 1.07 42.3

HF-LPMEDMPI

0.95 0.93 0.80 0.95 0.93 0.92 0.81 0.93 0.90 0.06 7.00LLE 0.81 0.70 0.69 0.64 0.74 1.11 1.40 1.47 0.94 0.34 35.6

HF-LPMETs/(Ts + Tm)

0.76 0.75 0.75 0.73 0.76 0.75 0.75 0.75 0.75 0.01 1.32LLE 0.72 0.74 0.72 0.73 0.72 0.73 0.71 0.69 0.72 0.02 2.28

HF-LPMETs/C30�� hopane

0.42 0.41 0.41 0.42 0.43 0.41 0.40 0.39 0.41 0.01 3.07LLE 0.76 0.81 0.94 0.96 0.79 0.87 0.47 0.42 0.75 0.20 26.9

HF-LPMEC30 rearranged hopane/C30�� hopane

0.19 0.21 0.20 0.19 0.20 0.20 0.20 0.21 0.20 0.01 4.11LLE 0.19 0.20 0.20 0.19 0.18 0.19 0.17 0.17 0.19 0.01 7.59

HF-LPMEC30�� moretane/C30�� hopane

0.12 0.09 0.10 0.07 0.08 0.09 0.09 0.12 0.10 0.02 20.7LLE 0.09 0.09 0.08 0.08 0.09 0.09 0.10 0.09 0.09 0.01 6.22

HF-LPMEC29��/C30�� hopane

0.41 0.43 0.42 0.41 0.41 0.41 0.42 0.42 0.42 0.01 1.81LLE 0.50 0.53 0.55 0.55 0.51 0.53 0.43 0.43 0.50 0.05 9.74

HF-LPME18�(H)-oleanane/C30�� hopane

0.11 0.11 0.10 0.11 0.11 0.11 0.11 0.10 0.11 0.01 5.21LLE 0.09 0.13 0.13 0.12 0.11 0.13 0.13 0.11 0.12 0.01 11.1

HF-LPMEC29Ts/(C29Ts + C29�� hopane)

0.44 0.42 0.44 0.46 0.44 0.44 0.43 0.43 0.44 0.01 2.68LLE 0.45 0.43 0.43 0.44 0.43 0.44 0.45 0.45 0.44 0.01 1.96

HF-LPMEC31 hopane (22S/22S + 22R)

0.56 0.55 0.55 0.56 0.56 0.58 0.55 0.55 0.56 0.01 1.45LLE 0.58 0.58 0.61 0.60 0.61 0.56 0.58 0.60 0.59 0.02 2.76

HF-LPMEC30 rearranged hopane/C29Ts

0.59 0.67 0.60 0.55 0.61 0.62 0.62 0.68 0.62 0.04 7.28LLE 0.47 0.48 0.48 0.42 0.47 0.46 0.48 0.47 0.47 0.02 4.05

* DMNR = (1,3-DMN + 1,6-DMN)/(1,5-DMN + 1,4-DMN); TMNR = 2,3,6-TMN/(1,4,6-TMN + 1,3,5-TMN); TeMNR = 1,3,6,7-TeMN/(1,3,6,7-TeMN + 1,2,5,6-TeMN + 1,2,3,5-TeMN); MPR = 2-MP/1-MP; MPI-1 = 1.5(3-MP + 2-MP)/(P + 9-MP + 1-MP); MPI-2 = (3-MP + 2-MP)/(9-MP + 1-MP); PAI = (1- + 2- + 3- + 9-MP)/P; DMPI = 4(2,6- + 2,7- + 3,5- + 3,6-DMP + 1- + 2- + 9-EP)/(P + 1,3- + 1,6- + 1,7- + 2,5- + 2,9- + 2,10- + 3,9- + 3,10-DMP); DMN – dimethylnaphthalene; TMN –trimethylnaphthalene; TeMN – tetramethylnaphthalene; P – phenanthrene; MP – methylphenanthrene; EP – ethylphenanthrene; DMP – dimethylphenanthrene.

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According to the evaluation method of indices suggested bytout et al. [24], relative standard deviation (%RSD) is considereds an indicator to evaluate the variability of diagnostic indices inhe weathering simulating experiments. The indices with %RSD <5%re probably not affected by short-term weathering and are avail-ble for correlating spilled oils to suspected sources. While %RSD inhe range of 5–10% indicates short-term weathering having slightffects on these indices, and the indices can assist in the sourcedentification of oil spills, and %RSD >10% indicates that weatheringas a remarkable effect on these indices and that the indices are

ess suitable for source determination.

.1. n-Alkanes and isoprenoids

Field observations of oil spills revealed that the >C20 n-alkanesan be well preserved at a relatively moderate level of degradation25]. Our previous laboratory study showed that the >C18 n-alkanesave no distinctive loss after 72 h of weathering degradation [23].ased upon the results above, the distribution patterns of n-alkanes

n the two simulating experiments are shown by using the ratio ofoncentration for each n-alkane and a concentration of C20 n-alkanen the same sample (Ci/C20) (Fig. 1), to eliminate differences amongample amounts, injection volumes and instruments.

As shown in Fig. 1a, the lowest carbon number of n-alkanesetected is 7 for samples prepared by the HF-LPME method. Withhe increase of weathering time, the relative contents of low-

olecular weight n-alkanes (n < 15) gradually reduce. After 24 h, theC12 n-alkanes have been completely degraded by weathering. In

ontrast, the distribution of >C15 n-alkanes have no distinctive vari-tion even after 72 h of weathering degradation for the HF-LPMEamples. Fig. 1b displays the distribution of n-alkanes in the sam-les pretreated by the conventional LLE method. As shown, even

n slightly weathered samples, the <C11 n-alkanes have not been

Fig. 1. Distribution of n-alkanes in the two

216 (2009) 6155–6161

detected. The comparison indicates that the LLE sample prepa-ration method has an obvious effect on the composition of the<C18 n-alkanes, especially for the lighter components with a car-bon number lower than 11. In addition, no obvious differences werefound in the range of the >C18 n-alkanes from the two pretreatmentmethods. Therefore, based on the distribution of n-alkanes, the HF-LPME technique is a more suitable sample pretreatment method foroil spill investigations.

Diagnostic indices of Pr/n-C17, Ph/n-C18, and Ph/Pr also supportthe above conclusion. The %RSD of these ratios are all less than 5%for the samples prepared by HF-LPME (Table 1), inferring that theywill be available indices for source identification of this spill. Butfor the LLE samples, only the ratio of Pr/n-C17 (<5%) is reliable forcorrelating spilled oils to suspected sources. The lower molecularweight hydrocarbons volatilize easier than the higher homologues,therefore, longer analytical times and evaporating concentrationsduring the LLE procedure are possibly the main reasons for thehigher ratios of Pr/n-C17, Ph/n-C18 and Pr/Ph in samples treated byLLE.

3.2. Polycyclic aromatic hydrocarbons

In PAHs, naphthalene, phenanthrene and their alkyl deriva-tives are used to compare the two sample preparation methods.As shown in Fig. 2, for the samples prepared by HF-LPME, smallamounts of naphthalene and C1-naphthalene can still be detectedafter 72 h of weathering time. And the contents of C2-, C3-, and C4-naphthalene vary only a little. However, for the samples prepared

by LLE, even with less than 1 h of weathering time, naphthalenehas been completely lost and the content of C1-naphthalene is verylow. After 24 h of weathering, C1- and C2-naphthalene are com-pletely lost, and the amount of C3-naphthalene clearly decreases.Meanwhile, Fig. 2 shows that relative contents of phenanthrene and

weathering simulation experiments.

Y. Li et al. / J. Chromatogr. A 1216 (2009) 6155–6161 6159

Fig. 2. Multiple ion mass chromatograms showing the distributions of naphthalene, phenanthrene and their alkyl derivatives in representative samples by using two samplepreparation methods. (A) m/z 128 + 142 + 156 + 170 + 184; (B) m/z 178 + 192 + 206 + 220.

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1–C3 phenanthrenes do not have considerable changes during theeathering procedure for the samples treated by HF-LPME, but for

he samples treated by LLE, phenanthrene and C1-phenanthreneecrease obviously with the increase of weathering time. There-

ore, like the conclusion from the alkane distributions, using theF-LPME method obtains more information on lighter aromaticydrocarbons due to the reduced analytical time, simple operat-

ng steps, and lack of evaporating concentration and does not differonsiderably in the high-molecular weight fractions.

Since naphthalene, phenanthrene, and their correspondinglkylated homologues are easily degraded by weathering and rel-tively bad gas chromatographic separation for multiple alkylatedAHs make their exact measurements more difficult, most indicesased on these compounds have a relatively high %RSD (Table 1),

ndicating that they are not available for source identification ofil spills. However, except for MPR and DMNR, the %RSD of other

ndices from HF-LPME is less than 10%, suggesting that these indicesan be used as an assistant evidence for source identification of oilpills.

.3. Biomarkers

Biomarkers are complex “molecular fossils” derived from onceiving organisms. Their source-specific structure can be well pre-erved in oil, bitumen, rocks, and sediments and can be largelyarried forward during refining [26]. Due to greater resistanceo weathering degradation, terpane and sterane biomarkers areidely used for source identification of oil spills [27].

Table 1 presents some common diagnostic indices based onerpane biomarker compounds. Because biomarkers are highlyesistant to weathering degradation, the indices based on theseompounds in residual oils are considered to be stable during theeathering procedure of spilled oils. As expected, most indices

f terpane biomarkers have lower standard deviations and %RSDTable 1). For example, in the samples treated by HF-LPME, except

or the ratio of C30�� moretane/C30�� hopane (%RSD >10%), thethers (%RSD <10%) can be used as reliable or assistant indices forource identification of this oil spill. The comparison shows thatinor differences are observed between the mean values of terpane

iomarker parameters for the samples in the two simulating exper-

able 2arbon isotopic composition of individual n-alkanes by HF-LPME.

-Alkanes Oil 0.1 h 1 h 2 h 5 h

9 −28.6 −28.5 – – –10 −29.0 −28.7 −28.6 −28.4 −28.211 −29.2 −29.1 −29.1 −28.5 −28.512 −29.6 −29.5 −29.3 −29.3 −29.513 −29.6 −29.2 −29.3 −29.1 −29.414 −30.2 −29.8 −29.9 −29.8 −29.715 −30.1 −29.8 −29.9 −30.1 −29.716 −30.4 −30.1 −30.1 −30.4 −30.617 −30.7 −30.3 −30.2 −30.6 −30.318 −30.5 −30.5 −30.6 −30.9 −30.619 −31.0 −31.4 −31.3 −30.9 −31.120 −31.1 −31.3 −31.1 −31.2 −31.521 −31.2 −31.5 −31.4 −31.0 −31.422 −30.6 −30.4 −30.6 −30.3 −30.523 −30.4 −30.0 −29.6 −29.8 −29.724 −30.2 −29.8 −29.9 −29.5 −29.825 −29.5 −29.6 −29.5 −30.0 −29.726 −29.9 −29.2 −29.4 −29.5 −29.927 −29.6 −29.3 −29.6 −29.5 −29.928 −29.3 −29.6 −29.3 −29.5 −29.529 −29.1 −29.0 −29.2 −29.2 −29.430 −29.2 −29.2 −29.5 −29.0 −29.831 −29.1 −28.8 −29.8 −29.7 −29.432 – – −29.2 −29.4 −28.933 – – – – −29.6

216 (2009) 6155–6161

iments, except for the indices of C30 rearranged hopane/C30��hopane and C29��/C30�� hopane, indicating that HF-LPME tech-nique has no considerable effects on the terpane distribution.Furthermore, %RSD of most ratios for the HF-LPME treating sam-ples is less than that for the samples prepared by LLE, and thisto some extent supports the premise that the HF-LPME method ismore stable than the LLE technique. Fewer steps and simple opera-tions produce relatively lower systematic and accidental errors forthe HF-LPME method.

The oil sample used in this study contains a very low con-centration of steranes and relatively more rearranged steranes,resulting in those sterane-related biomarker indices that are notwell detected. Accordingly, the information from these compoundsis not discussed here.

3.4. ı13C values of individual n-alkanes

Gas chromatography–isotope ratio mass spectrometry(GC–IRMS) is a useful tool for identifying sources of organicmatter [28,29] and correlating oil with possible source rocks[30,31]. Previous studies have proven that stable carbon iso-topic composition of individual n-alkanes can provide additionalevidence that helps to trace oil spill sources [23,32,33].

Table 2 illustrates that the standard deviations (SD) of �13C val-ues of n-C9–n-C33 for the HF-LPME treating samples vary from 0.1‰to 0.3‰, falling within the range of analytical error. The %RSD of n-alkanes are all less than 5%, suggesting that short-term weatheringhas no obvious effects on the �13C values of individual n-alkanes.

As shown in Fig. 3, carbon isotopic profiles of individual n-alkanes obtained by two sample preparation methods have almostidentical distributions, indicating that no obvious isotopic frac-tionation occurs during the HF-LPME procedure, and the lack ofpurification steps also has no remarkable influence on �13C val-ues of individual n-alkanes extracted by HF-LPME. In addition, dueto the lack of additional evaporation of the extract, the HF-LPME

technique can determine relatively lower molecular weight com-pounds (such as n-C9–n-C11) than those by the LLE method. It isparticularly useful for source identification of the lighter distillates,such as diesel oils. Therefore, HF-LPME can be a promising way toidentify oil spill sources.

24 h 48 h 72 h Mean SD %RSD

– – – −28.5 0.1 0.4– – – −28.6 0.3 0.9– – – −28.9 0.3 1.2−29.3 −29.0 −28.7 −29.3 0.3 1.1−29.5 −29.4 −29.1 −29.3 0.2 0.6−30.0 −30.2 −29.9 −29.9 0.2 0.6−29.8 −29.8 −29.8 −29.9 0.1 0.5−30.3 −30.2 −30.2 −30.3 0.2 0.6−30.2 −30.3 −30.1 −30.3 0.2 0.7−30.6 −30.5 −30.5 −30.6 0.1 0.4−31.2 −30.7 −31.1 −31.1 0.2 0.7−31.4 −31.2 −31.4 −31.3 0.1 0.4−31.2 −31.6 −31.4 −31.3 0.2 0.6−30.5 −30.5 −30.3 −30.4 0.1 0.4−29.8 −30.0 −30.0 −29.9 0.2 0.8−29.9 −29.9 −29.9 −29.9 0.2 0.6−29.7 −29.9 −29.4 −29.7 0.2 0.7−29.4 −29.7 −29.4 −29.6 0.3 0.9−29.6 −29.5 −29.5 −29.6 0.2 0.6−29.5 −29.5 −29.6 −29.5 0.1 0.4−29.6 −29.9 −29.0 −29.3 0.3 1.0−29.2 −29.3 −29.4 −29.3 0.3 0.9−28.9 −28.8 −29.0 −29.2 0.4 1.4−29.0 −29.2 −29.2 −29.2 0.2 0.6−29.6 −30.0 −29.6 −29.7 0.2 0.8

Y. Li et al. / J. Chromatogr. A 1216 (2009) 6155–6161 6161

F paratin iation

4

LeHt

2

3

tLeadcpnIai

ps

A

o

[

[[[

[[

[

[[[[[[[[

[

[[[29] J.M. Hayes, K.H. Freeman, B.N. Popp, C.H. Hoham, Org. Geochem. 16 (1990)

1115.

ig. 3. Carbon isotopic profiles of individual n-alkanes extracted by two sample pre-alkanes from the spilled oil and the source oil. Short line represents standard dev

. Conclusion

The simulation experiment of oil spills, coupled with the HF-PME technique, was compared with the weathering simulatingxperiment performed months ago, in order to clarify whether theF-LPME sample preparation method is available for oil spill inves-

igation. The above discussion reveals that:

1. Compared with the conventional LLE sample preparing method,HF-LPME can detect more information about the low-molecularweight compounds, such as C7–C11 n-alkanes, naphthalene,phenanthrene, and �13C values of n-C9–n-C11.

. No obvious difference was found between the distributions ofrelatively high-molecular weight compounds extracted by LLEand HF-LPME, such as >C18 n-alkanes, C1–C3 phenanthrene, andhopanes.

. Carbon isotopic profiles of n-alkanes for the samples in the twosimulating experiments are identical, indicating that the HF-LPME method has no remarkable effects on the carbon isotopiccompositions of individual n-alkanes.

The conclusions confirm that the HF-LPME sample prepara-ion technique can gain exact results just like the conventionalLE sample pretreatment method. Also, the HF-LPME technique isxtraordinary fast, needing only about 2 h for sample preparationnd sample analysis, whereas the LLE method requires one or twoays from sample pretreatment to analysis. Because hollow fiberan prevent the interferences caused by large molecules or sus-ended solid particles in sample solutions, an extra process is notecessary to purify the sample solution, which saves a lot of time.

n oil spill samples, the content of the analytes is rich enough fornalyzing, so the advantage of enrichment of the HF-LPME methods not taken into account in this paper.

Therefore, HF-LPME, as a simple, fast, and inexpensive samplereparation technique, can become a promising way to identify oilpill sources.

cknowledgements

This work was financially supported by the Earmarked Fundf the State Key Laboratory of Organic Geochemistry (Grant No.

[[[[

on methods (LLE and HF-LPME). Dots show the average of �13C values of individualof �13C values for each individual compound.

SKLOG2008A02) and the National Key Technology R&D Program(Grant No. 2006BAC11B03). We are grateful to H.S. Chen and T.S.Xiang for technical assistance and the two reviewers for their help-ful suggestions.

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