Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography-diode array detection as an efficient and sensitive technique for determination of antioxidants

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<ul><li><p>Analytica Chimica Acta 591 (2007) 6979</p><p>Dispersive liquidliquid microextraction foldeina,</p><p>mia UP.O.arch 22007</p><p>Abstract</p><p>Dispersiv uid cpresented fo os 16at microliter e sohigh speed, on sois between 3 and 7 ng mL1. One variable at a time optimization and response surface modeling were used to obtain optimum conditions formicroextraction procedure and nearly same experimental conditions were obtained using both optimization methods. Recoveries in the ranges7886% and 84110% were obtained by one variable at a time and response surface modeling, respectively. Using tap water and packed water asmatrices do not show any detrimental effect on the extraction recoveries and enrichment factors of analytes. 2007 Else</p><p>Keywords: DResponse surf</p><p>1. Introdu</p><p>Plastic aticizers halife of platies of thesin small a1%) are dilike thermocross-linkinthe deterior</p><p>Plastic amigrationEuropean C-tions (mossafety of fo</p><p> CorresponE-mail ad</p><p>0003-2670/$doi:10.1016/jvier B.V. All rights reserved.</p><p>ispersive liquidliquid extraction; Antioxidant; High-performance liquid chromatography; Sample preparation; One variable at a time optimization;ace modeling</p><p>ction</p><p>dditives such as antioxidants, stabilizers and plas-ve a major influence in the processing and shelfstics and are responsible for many of the proper-e materials [1]. Plastics additives, which are presentmounts in plastics (generally ranging from 0.1 tospersed in the polymer matrix and prevent effects-oxidative deterioration, which initiates cleavage andg of the macromolecular chains and, consequently,ation of the polymer [2].dditives have relatively low molecular weights and</p><p>mechanisms into foods are often of concern. Theommission has adopted the policy of using restric-tly specific migration limits, SMLs) to control theod contact materials and articles. There are several</p><p>ding author. Tel.: +46 46 222 8169; fax: +46 46 222 4544.dress: jan ake.jonsson@analykem.lu.se (J.A. Jonsson).</p><p>hundred SMLs in Directive 2002/72/EC [3] and amendments,which have been assigned to plastic monomers and additives.A small number of analytical methods have been validated formeasuring migration of substances; most of these only apply tofood owing to the complexity of foods. The determination ofplastic additives in food matrices is associated with two maindifficulties. The first is the low detection level required, as thesesubstances are present in small amounts. The second one is thediversity of potential interferences present in foodstuffs [4]. Ingeneral, extraction techniques such as extraction with solvents[5,6] and solid phase extraction [6,7] are used to clean up and pre-concentrate the additives. Traditional extraction techniques useconsiderable volumes of expensive and toxic organic solvents.Recently Assadi and coworkers reported a new liquidliquidextraction technique namely dispersive liquidliquid microex-traction (DLLME) which uses microliter volumes of extractionsolvent along with a few milliliters of dispersive solvents such asmethanol, acetonitrile, acetone or THF. They applied this techni-que for preconcentration of organophosphorus pesticides [8] andpolycyclic aromatic hydrocarbons [9] from aqueous samples.</p><p> see front matter 2007 Elsevier B.V. All rights reserved..aca.2007.03.040liquid chromatography-diode arrayand sensitive technique for determ</p><p>Mir Ali Farajzadeh a, Morteza Bahrama Department of Chemistry, Faculty of Science, Ur</p><p>b Department of Analytical Chemistry, University of Lund,Received 24 January 2007; received in revised form 15 M</p><p>Available online 25 March</p><p>e liquidliquid microextraction (DLLME) and high performance liqr extraction and determination of Irganox 1010, Irganox 1076 and Irgaf</p><p>volume level and acetonitrile were used as extraction and dispersivhigh enrichment factor, high recovery, good repeatability and extractilowed by high-performancetection as an efficientation of antioxidantsJan Ake Jonsson b,niversity, Urmia, Iran</p><p>Box 124, 221 00 Lund, Sweden007; accepted 16 March 2007</p><p>hromatography-diode array detection (HPLC-DAD) was8 (antioxidants) in aqueous samples. Carbon tetrachloride</p><p>lvents, respectively. The main advantages of method arelvent volume at L level. Limit of detection for analytes</p></li><li><p>70 M.A. Farajzadeh et al. / Analytica Chimica Acta 591 (2007) 6979</p><p>In this work, we examined the applicability of partial facto-rials design at five levels for simultaneous optimization of ninefactors affecting the DLLME-HPLC-DAD analyzing procedureof three polymer additives. The one variable at a time opti-mization of the same analyses had shown that some parametershave no importance or at least have low significance. Therefore,we could select only the main factors for study but in order torecheck the significance of each variable in model, as well inorder to evaluate applicability of fractional factorial design allnine variables were included in optimization. MLR was used tobuild the optimization model.</p><p>2. Experimental</p><p>2.1. Chemicals</p><p>Irganox 1076 (Scheme 1) was obtained from Sigma (St.Louis, MOwere giftsCompanyther purificgrade), carran (THF),were purchwater usedUSA).</p><p>2.2. Stand</p><p>Due tothe polymechloride tosolution isstandard soFor this pu11 mL glasThe residuprepare stainjected toity controlof enrichm</p><p>Sch</p><p>was prepared by dilution of the above standard solution inreagent water (400 ng mL1).</p><p>Tap watory. PackeSweden).</p><p>2.3. HPLC</p><p>Separati1076 andequipped wSeries 105was linkedwere perfobax Extendsize) frommethanol w</p><p>Dete</p><p>ispe</p><p>.00in aas dextrn bywas</p><p>-1,oplebe (arredLC s</p><p>he rejectemedes o</p><p>tatist</p><p>com</p><p>peried in</p><p>ults</p><p>his swithinato o</p><p>of dilvenbothingtrac) an, USA). Irganox 1010 and Irgafos 168 (Scheme 1)from Petrochemical Research and Technology</p><p>(Tehran, Iran) and used as received without fur-ation. Other chemicals such as methanol (HPLC</p><p>bon tetrachloride, toluene, acetonitrile, tetrahydrofu-sodium chloride and sodium dihydrogen phosphateased from Merck (Darmstadt, Germany). All reagentwas purified with a Milli-Q system (Bedford, MA,</p><p>ard solutions and real samples</p><p>the limited solubility of Irgafos 168 in methanol,r additives were initially dissolved in carbon tetra-prepare a stock solution (each 1000g mL1). Thisstable for at least 2 months at room temperature. Alution of additives in methanol was prepared daily.rpose 200L stock solution was transferred to a</p><p>s vial and the solvent was evaporated in a water bath.e was dissolved in 10 mL HPLC grade methanol tondard solution (each 20g mL1). This solution wasthe separation system each day (three times) for qual-and the obtained peak areas were used in calculationent factors and recoveries. Working standard solution</p><p>eme 1. Chemical structure of the selected antioxidants.</p><p>phase.</p><p>2.4. D</p><p>A 5placed(2 mL)ride assolutioducedFP 510fine drtest tutransfeL HPbath, tand inperforof curv</p><p>2.5. S</p><p>Theand Exwas us</p><p>3. Res</p><p>In tbineddetermples. Teffecttion sousingmodeltors, exEqs. (1ter samples were collected fresh from our labora-d waters were purchased from a local store (Lund,</p><p>-diode array detection (DAD) system</p><p>on and determination of Irganox 1010, IrganoxIrgafos 168 were carried out on an HPLC system</p><p>ith a photodiode array detector (Hewlett-Packard0) (Agilent, Wilmington, DE, USA) The instrumentto an Hewlett-Packard ChemStation. All injectionsrmed manually with 26.5L sample loop. A Zor--C18 column (100 mm 2.1 mm, 3.5m particleAgilent was employed at room temperature. Pureas used at a flow rate 0.5 mL min1 as a mobilection was performed at = 210 nm.</p><p>rsive liquidliquid microextraction procedure</p><p>mL working standard solution (400 ng mL1) was12-mL glass tube with conical bottom. Acetonitrileispersive solvent, containing 40L carbon tetrachlo-action solvent, was injected rapidly into the sample</p><p>using a 5-mL syringe. The cloudy solution pro-centrifuged for 5 min at 2000 rpm (Lab systems OyHelsinki, Finland). After centrifuging, the dispersedts of carbon tetrachloride sedimented in the bottom ofbout 30L). The sedimented phase was completelyto another test tube with conical bottom using 100-yringe and after evaporation of the solvent in a watersidue was dissolved in 50L HPLC grade methanold into the separation system. All experiments werein duplicate and means of results were used in plottingr in tables.</p><p>ical software</p><p>puter software EREGRESS, Essential Regressionmental Design for Chemists and Engineers [1012],</p><p>this study.</p><p>and discussion</p><p>tudy dispersive liquidliquid microextraction com-HPLC-DAD was used for preconcentration and</p><p>ion of the selected antioxidants in aqueous sam-btain a high recovery and enrichment factor, thefferent factors such as type of dispersive and extrac-ts their volumes, pH, salt addition, etc. were testedthe one variable at a time and response surface</p><p>approaches. In order to study the mentioned fac-tion recovery and enrichment factor have been used.d (2) were used for calculation of enrichment factor</p></li><li><p>M.A. Farajzadeh et al. / Analytica Chimica Acta 591 (2007) 6979 71</p><p>and recovery:</p><p>EF = CsedC0</p><p>(1)</p><p>where EF, Csed and C0 are the enrichment factor, concentra-tion of analyte in sedimented phase and initial concentration ofanalyte in aqueous sample, respectively.</p><p>R =[ (Csed Vsed)</p><p>(C0 Vaq)]</p><p>= EF (</p><p>VsedVaq</p><p>)(2)</p><p>where R, Vsed and Vaq are the extraction recovery, volume of sed-imented phase and volume of aqueous sample, respectively. Csedwas calculated by comparing peak areas of concentrated solu-tion with those of standard solution (20g mL1) in methanolinjected to HPLC.</p><p>3.1. One variable at a time optimization</p><p>In DLLME extraction, solvent(s) has to satisfy the followingvariety of requirements: (1) its density should be higher thanwater; (2) it should extract the analytes; (3) it should form acloudy solution in the presence of a dispersive solvent wheninjected to an aqueous solution (form very tiny droplets) andfinally (4) it should show a good chromatographic behavior (itshould not absorb radiation at the detection wavelength of ana-lytes and also it should not have elution strength higher thanmobile phase used in the separation system). Among the solventswith density higher than water (mainly chlorinated solvents),</p><p>dichloromethane, chloroform and carbon tetrachloride weretested. On the other hand, the selection of a dispersive solvent islimited to solvents such as methanol, acetonitrile, tetrahydrofu-ran and acetone, that are miscible with both water and extractionsolvents. In this study all combinations of CH2Cl2, CHCl3 andCCl4 (50L) as extraction solvents and methanol, acetonitrile,tetrahydrofuran (THF) and acetone (1 mL) as dispersive sol-vents were tested. In the case of CH2Cl2 as extraction solvent, atwo-phase system was not observed with any studied dispersivesolvents when they were injected to 5 mL analytes solution inwater. In the case of CHCl3 only with THF as dispersive sol-vent, a two-phase system was achieved. It should be noted thatin this case the volume of sedimented phase was 260L, whichis a reason for obtaining low EFs. Also it seems that Irgafos 168decomposes in the presence of THF and no peak was observedin the chromatogram in its retention time after extraction (seebelow). With CCl4 as extraction solvent, a two-phase systemwas formed with all four dispersive solvents. In Fig. 1 EF and Rwere plotted as a function of type of dispersive solvent. As canbe seen, EF for all analytes is high using methanol comparedto other solvents. In order to obtain relatively higher EF and Rwe have to also consider the volume of sedimented phase (20,57, 367 and 42L for methanol, acetonitrile, THF and acetone,respectively). By applying these volumes and obtaining R for theanalytes, it can be concluded that acetonitrile has an advantageover the other solvents. For this reason carbon tetrachloride andacetonitrile were chosen as extraction and dispersive solvents,respectively, in the following studies.</p><p>Fig. 1. Effect xtract1 mL; extractiof dispersive solvent on the enrichment factor and recovery of antioxidants. Eon solvent, 50L CCl4.ion conditions: sample volume, 5 mL; dispersive solvent volume,</p></li><li><p>72 M.A. Farajzadeh et al. / Analytica Chimica Acta 591 (2007) 6979</p><p>Fig. 2. Effect of dispersive solvent volume on the enrichment factor ofantioxidants. Extraction conditions: sample volume, 5 mL; dispersive solvent,acetonitrile; extraction solvent, 50L CCl4.</p><p>3.1.1. Selection of dispersive solvent (acetonitrile) volumeIn order to study the effect of acetonitrile volume, the vol-</p><p>ume was v</p><p>obtained revolume ofvolumes, Ewas observvent, the seof 3 mL) aobtained rethe dispers</p><p>3.1.2. Selevolume</p><p>In orderthe performvolumes ovals) and a1.5 mL) weno two-phaof sedimenversus voluFig. 3, by i</p><p>Fig. 3. Volumtion conditionextraction sol</p><p>Fig. 4. Effect of the volume of extraction solvent (CCl4) on the enrichmentfactor of antioxidants. Extraction conditions: sample volume, 5 mL; dispersivesolvent, 1.5 mL acetonitrile.</p><p>to 100L, the volume of sedimented phase increases from 6 to95L. Also the recovery of analytes increased. But due to theincreasing sedimented phase volume at higher extraction solvent</p><p>es, the ofare o</p><p>re hiwas</p><p>reduilityfactmixtactioif lethanof e</p><p>mentnctio. 6 its thef Irgareaser, titharied in the range 03 mL in 0.5-mL intervals. Thesults are shown in Fig. 2 as EF. By increasing the</p><p>acetonitrile EF and R increased till 1.5 mL. At higherF remained constant whereas R was decreased. Ited that by increasing the volume of dispersive sol-dimented phase volume decreased (15L in the casend consequently recovery also decreased. From thesults 1.5 mL was chosen as an optimum volume forive solvent.</p><p>ction of extraction solvent (carbon tetrachloride)</p><p>to study the effect of extraction solvent volume onance of the presented DLLME procedure, different</p><p>f carbon tetrachloride (20100L at 10-L inter-constant volume of dispersive solvent (acetonitrile,re tested. With less than 30L carbon tetrachloridese system was observed. Figs. 35 show the variationted phase volume, enrichment factor and recoveryme of extraction solvent, respectively. According toncreasing the volume of extraction solvent from 30</p><p>volumvolumand Rlytes a70L</p><p>Topossibof thewater,as extrusefulhigherbottomenrichas a fuin Fig1076 icase o</p><p>EF decHowevvents we of sedimented phase vs. extraction solvent volume. Extrac-s: sample volume, 5 mL; dispersive solvent, 1.5 mL acetonitrile;vent, CCl4.</p><p>Fig. 5. Effectantioxidants.1.5 mL acetone enrichment factor decreased in those volumes. Theextraction solvent should be selected so that high EFbtained. In the range of 5070L recoveries of ana-gh and EFs are acceptable. In the following studiesselected as the optimal volume of extraction solvent.ce the use of chlorinated solvent (CCl4) and study ofof using less toxic solvents and with considerationthat most organic solvents have density lower thanures of toluene and carbon tetrachloride were testedn solvent. The fraction of toluene in the mixture wasss than 70% because those mixtures have a densitywater and the extraction solvent is collected in thextraction vessel after centrifuging. In Figs. 6 and 7,factor and volume of sedimented phase are plottedn of toluene fra...</p></li></ul>

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