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  • Analytica Chimica Acta 591 (2007) 6979

    Dispersive liquidliquid microextraction foldeina,

    mia UP.O.arch 22007

    Abstract

    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

    Keywords: DResponse surf

    1. Introdu

    Plastic aticizers halife of platies of thesin small a1%) are dilike thermocross-linkinthe deterior

    Plastic amigrationEuropean C-tions (mossafety of fo

    CorresponE-mail ad

    0003-2670/$doi:10.1016/jvier B.V. All rights reserved.

    ispersive liquidliquid extraction; Antioxidant; High-performance liquid chromatography; Sample preparation; One variable at a time optimization;ace modeling

    ction

    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

    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

    ding author. Tel.: +46 46 222 8169; fax: +46 46 222 4544.dress: jan ake.jonsson@analykem.lu.se (J.A. Jonsson).

    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.

    see front matter 2007 Elsevier B.V. All rights reserved..aca.2007.03.040liquid chromatography-diode arrayand sensitive technique for determ

    Mir Ali Farajzadeh a, Morteza Bahrama Department of Chemistry, Faculty of Science, Ur

    b Department of Analytical Chemistry, University of Lund,Received 24 January 2007; received in revised form 15 M

    Available online 25 March

    e liquidliquid microextraction (DLLME) and high performance liqr extraction and determination of Irganox 1010, Irganox 1076 and Irgaf

    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

    Box 124, 221 00 Lund, Sweden007; accepted 16 March 2007

    hromatography-diode array detection (HPLC-DAD) was8 (antioxidants) in aqueous samples. Carbon tetrachloride

    lvents, respectively. The main advantages of method arelvent volume at L level. Limit of detection for analytes

  • 70 M.A. Farajzadeh et al. / Analytica Chimica Acta 591 (2007) 6979

    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.

    2. Experimental

    2.1. Chemicals

    Irganox 1076 (Scheme 1) was obtained from Sigma (St.Louis, MOwere giftsCompanyther purificgrade), carran (THF),were purchwater usedUSA).

    2.2. Stand

    Due tothe polymechloride tosolution isstandard soFor this pu11 mL glasThe residuprepare stainjected toity controlof enrichm

    Sch

    was prepared by dilution of the above standard solution inreagent water (400 ng mL1).

    Tap watory. PackeSweden).

    2.3. HPLC

    Separati1076 andequipped wSeries 105was linkedwere perfobax Extendsize) frommethanol w

    Dete

    ispe

    .00in aas dextrn bywas

    -1,oplebe (arredLC s

    he rejectemedes o

    tatist

    com

    peried in

    ults

    his swithinato o

    of dilvenbothingtrac) an, USA). Irganox 1010 and Irgafos 168 (Scheme 1)from Petrochemical Research and Technology

    (Tehran, Iran) and used as received without fur-ation. Other chemicals such as methanol (HPLC

    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,

    ard solutions and real samples

    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

    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

    eme 1. Chemical structure of the selected antioxidants.

    phase.

    2.4. D

    A 5placed(2 mL)ride assolutioducedFP 510fine drtest tutransfeL HPbath, tand inperforof curv

    2.5. S

    Theand Exwas us

    3. Res

    In tbineddetermples. Teffecttion sousingmodeltors, exEqs. (1ter samples were collected fresh from our labora-d waters were purchased from a local store (Lund,

    -diode array detection (DAD) system

    on and determination of Irganox 1010, IrganoxIrgafos 168 were carried out on an HPLC system

    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.

    rsive liquidliquid microextraction procedure

    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

    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.

    ical software

    puter software EREGRESS, Essential Regressionmental Design for Chemists and Engineers [1012],

    this study.

    and discussion

    tudy dispersive liquidliquid microextraction com-HPLC-DAD was used for preconcentration and

    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

    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

  • M.A. Farajzadeh et al. / Analytica Chimica Acta 591 (2007) 6979 71

    and recovery:

    EF = CsedC0

    (1)

    where EF, Csed and C0 are the enrichment factor, concentra-tion of analyte in sedimented phase and initial concentration ofanalyte in aqueous sample, respectively.

    R =[ (Csed Vsed)

    (C0 Vaq)]

    = EF (

    VsedVaq

    )(2)

    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.

    3.1. One variable at a time optimization

    In DLLME extractio

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