A new device for magnetic stirring-assisted dispersive liquid–liquid microextraction of UV filters in environmental water samples

Download A new device for magnetic stirring-assisted dispersive liquid–liquid microextraction of UV filters in environmental water samples

Post on 29-Oct-2016

224 views

Category:

Documents

3 download

Embed Size (px)

TRANSCRIPT

<ul><li><p>Talanta 83 (2011) 17111715</p><p>Contents lists available at ScienceDirect</p><p>Talanta</p><p>journa l homepage: www.e lsev ier .com</p><p>A new spemicroe l w</p><p>Ping-PinKey Laboratory cation</p><p>a r t i c l</p><p>Article history:Received 31 JuReceived in re22 NovemberAccepted 30 NAvailable onlin</p><p>Keywords:Dispersive liqu(DLLME)UV lters1-OctanolHPLC-UV</p><p>iquidHPLCopenoptininaryDLLMhe tws easng in</p><p>oating above the sample solution, was elevated and concentrated into the narrow open tip of the askby adding pure water into it via the other port, which was withdrawn with a microsyringe for the sub-sequent HPLC analysis. Under the optimized conditions, the limits of detection for the analytes were inrange of 0.20.8ngmL1 .The linearity ranges were 820,000ngmL1 for HB, 720,000ngmL1 for DB,810,000ngmL1 for BP and 520,000ngmL1 for HMB, respectively. Enrichment factors ranging from</p><p>1. Introdu</p><p>Analyticas biologicSo, developsample-preical chemistconcentrateconventionextractionneeds of sadecades, mturized andsolid-phase(LPME), etc</p><p>Recentlynewly deveto the meritwell as high</p><p> CorresponE-mail add</p><p>0039-9140/$ doi:10.1016/j.59 to 107 folders were obtained for the analytes. The relative standard deviations (n=3) at a spiked levelof 80ngmL1 were between 1.4 and 4.8%. The proposed magnetic stirring-assisted DLLME method wassuccessfully applied to the analysis of lake water samples.</p><p> 2010 Elsevier B.V. All rights reserved.</p><p>ction</p><p>al instruments cannot handle complex samples suchal, environmental and pharmaceutical ones directly.ing fast, simple, inexpensive and environment-friendlyparation methods is becoming a critical issue in analyt-ry [1]. The aim of sample preparation is to clean up andtarget analytes from complex matrices [2]. However,</p><p>al sample-preparation methods such as liquidliquidand solid-phase extraction may not always meet theving time, materials and labour. In the past severaluch effort has been devoted to developing new minia-economical sample-preparation techniques, includingmicroextraction and liquid-phase microextraction</p><p>. [3,4]., dispersive liquidliquid microextraction (DLLME), aloped LPME method, has attracted much attention dues of short extraction time, ease of operation, low cost asenrichment factors for analytes [516]. DLLME is com-</p><p>ding author. Tel.: +86 27 68754067; fax: +86 27 68754067.ress: shizg@whu.edu.cn (Z.-G. Shi).</p><p>monly based on a ternary solvent system in which a mixture of twotypes of organic solvent (disperser solvent and extraction solvent(extractant)) is quickly added into target aqueous sample solu-tions [6]. The disperser solvents (methanol, acetone, acetonitrile,etc.), which are miscible with both aqueous and organic phases,are involved to accelerate the extractionbecause it can facilitate thecontact betweenaqueous sample solution and theextractant.How-ever, in the present of disperser solvent, the extractant is difcultto be separated from the aqueous solution unless centrifugation ata high speed for a considerable time is employed. As centrifugationneeds additional instrument and cost extra time, it is a little tediousfor sample preparation. Moreover, centrifugation involved DLLMEcannot handle samples of large volumes because no approximateconical centrifuge tubes were readily available.</p><p>Herein, we presented a magnetic stirring-assisted DLLME basedon a homemade new device. To evaluate the effectiveness of themethod and the device, several UV lters in aqueous environmen-tal sampleswereusedasmodel analytes. Theextractionwascarriedout in a binary system composed of the extractant (1-octanol) andthe aqueous sample solution. No disperser solvent was present.To facilitate the mass transfer from the aqueous samples to theextractant, during extraction, magnetic stirring was involved. Afterextraction, the extractant was easily separated from the aque-</p><p>see front matter 2010 Elsevier B.V. All rights reserved.talanta.2010.11.076device for magnetic stirring-assisted dixtraction of UV lters in environmenta</p><p>g Zhang, Zhi-Guo Shi , Qiong-Wei Yu, Yu-Qi Fengof Analytical Chemistry for Biology and Medicine (Wuhan University), Ministry of Edu</p><p>e i n f o</p><p>ly 2010vised form2010ovember 2010e 8 December 2010</p><p>idliquid microextraction</p><p>a b s t r a c t</p><p>A new method based on dispersive lperformance liquid chromatography (designed ask, which has two narrowto facilitate the DLLME process. By adtion were conveniently achieved. A bsolvent (1-octanol) was used for theaccelerated by magnetic agitation of tsolvent from the aqueous sample wawhile. No centrifugation step involvi/ locate / ta lanta</p><p>rsive liquidliquidater samples</p><p>, Wuhan 430072, China</p><p>liquid microextraction (DLLME) in combination with high-) has been developed for the analysis of UV lters. A speciallynecks with one of them having a capillary tip, was employed</p><p>g such a device, the extraction and subsequent phase separa-solvent system of water sample and low-density extractionE and no disperser solvent was involved. The extraction waso phases. After extraction, phase separation of the extractionily achieved by leaving the extraction system statically for aclassical DLLME was necessary. The analyte-enriched phase,</p></li><li><p>1712 P.-P. Zhang et al. / Talanta 83 (2011) 17111715</p><p>ous phase by leaving the extraction system statically for a while(5min). No centrifugation step was necessary. Several experimen-tal parameters, which may inuence the extraction performance ofthe proposed method, were investigated.</p><p>2. Experimental</p><p>2.1. Chemicals and reagents</p><p>The UV lters, 4-hydroxybenzophenone (HB), 2,4-dihydroxybenzophenone (DB), benzophenone (BP) and2-hydroxy-4-methoxybenzophenone (HMB), were purchasedfrom Alfa Aesar (Tianjin, China). Hydrochloric acid, sodiumhydroxide and sodium chloride, 1-octanol, methanol and aceticacid of analytical grade were purchased from Shanghai GeneralChemical Rproduced b</p><p>2.2. Sample</p><p>Standardprepared byin a fridge pdiluting the</p><p>Environmzone in thea 0.22-mDLLME.</p><p>2.3. Extract</p><p>The extrdimensionsneck of 4 cm0.2mm in din diameter</p><p>2.4. Extract</p><p>Firstly, 4into the extmixture wanetic stirrinsample witstraightforw2, the liquidin the narrof 1-octanoand accuracdrawnanddexperimentextraction p</p><p>Table 1Chemical structures and some physicochemical properties of the UV lters.</p><p>Name Structure pKa LogKow</p><p>4-Hydroxyb</p><p>O</p><p>2,4-Dihydro(DB)</p><p>Benzopheno</p><p>roxy-4hoxybB)</p><p>anol</p><p>PLC a</p><p>expA, U299mparate of75mngth</p><p>ults</p><p>lterom senvlly ints-existing interference [1924]. As a result, a puricationenrichment procedure is necessary before analysis. Herein,etic stirring assisted DLLME method was proposed for their</p><p>tion. The chemical structures and some physicochemicalties of the UV lters are given in Table 1.</p><p>traction optimization</p><p>eral parameters, including extraction solvent volume,tion time, ionic strength, sample pH and stirring speed, werezed for the extraction. An aqueous sample (20mL) contain-ngmL1 of eachanalytewasused for all experiments. If beingphasized elsewhere, sample volume was 20mL and each</p><p>ment was carried out in triplicate.</p><p>Extraction solvent volumectanol is one of the most widely used organic extraction sol-n LPME, which has shown satised extraction performanceious analytes. In this study, it was adopted as the extrac-lvent. Its volume plays important role in DLLME because itces not only the extraction efciencybut also theHPLC sepa-1-Octanol of different volumes ranging from20 to 60Lwaseagent Factory (Shanghai, China). Ultrapure water wasy an Aike (Chengdu, China) water purication system.</p><p>preparation</p><p>stock solutions of the UV lters (1000mgL1) weredissolving each analyte in methanol and stored at 4 Crior to use. Working solutions were prepared daily bystandard stock solutions with ultrapure water.ental water samples were collected from a swimming</p><p>East Lake (Wuhan, China). They were ltrated throughmembrane and were adjusted to the pH of 7.0 prior to</p><p>ion apparatus</p><p>action is achieved in a homemade device (Fig. 1). Theof it are as follows: the volume is 253mL; Port 1 is ain length, with a capillary tip of 1.5 cm in length and</p><p>iameter; Port 2 is a neck of 12 cm in length and 1.5 cm.</p><p>ion procedures</p><p>0L of 1-octanol was slowly injected through Port 2raction device containing 20mL of sample solution. Thes magnetically agitated for 20min. After that, the mag-gwas stopped and the 1-octanol oated on the aqueoushin 5min. By tilting the ask to keep Port 1 (Fig. 1(C))ard and adding pure water into the ask through Portlevel was elevated and the 1-octanol was concentratedow branch tip of the bottle (Port 1). Although 40Ll was added for the extraction, to ensure repeatabilityy, 20L of the analyte-enriched 1-octanol was with-ilutedwith 80L ofmethanol forHPLC analysis. All thes were performed at least three times. The schematicrocedures were depicted in Fig. 1.</p><p>Fig. 1. Schematic of the extraction process.</p><p>2-Hydmet(HM</p><p>Kow: oct</p><p>2.5. H</p><p>Theford, Mand a(150mthe semixturwas 0.wavele</p><p>3. Res</p><p>UVtion frlead toGenerapollutathe coand/ora magnextracproper</p><p>3.1. Ex</p><p>Sevextracoptimiing80not emexperi</p><p>3.1.1.1-O</p><p>vents ifor vartion soinuenration.enzophenone (HB)</p><p>HO</p><p>7.95 3.07</p><p>xybenzophenone</p><p>OOH</p><p>OH</p><p>7.53 2.96</p><p>ne (BP)</p><p>O</p><p> 3.38</p><p>-enzophenone</p><p>OOH</p><p>O</p><p>7.56 3.52</p><p>water partition coefcient.</p><p>nalysis</p><p>eriment was carried on a HPLC system (Waters, Mil-SA) equipped with a 1525 binary high-pressure pump6 photodiode array detector. An Xterra C18 column3.9mm, 5m particle size) from Waters was used forion of the target analytes. The mobile phase was amethanol: 1% acetic acid (60:40, v/v). The ow rateLmin1. The injection volume was 10L. The detectionwas set at 254nm.</p><p>and discussion</p><p>s are widely used as cosmetic additives for the protec-olar radiation. However, excessive use of them wouldironmental pollution as well as health issues [17,18].t is difcult to directly determine this class of organicin real samples due to their low concentration and</p></li><li><p>P.-P. Zhang et al. / Talanta 83 (2011) 17111715 1713</p><p>6050403020</p><p>2</p><p>4</p><p>6</p><p>8</p><p>10</p><p>12</p><p>Pea</p><p>k ar</p><p>ea X</p><p>(10</p><p>4 )</p><p>Volume (uL)</p><p> HB DB BP HMB</p><p>Fig. 2. Optimization of the extraction solvent volume. Other conditions: extractiontime, 20min; ionic strength, 0mmol L1; pH of sample solution, 7.0; stirring speed,1300 rpm.</p><p>studied to examine its inuence on the extraction performance.The results are shown in Fig. 2. It can be observed that the bestextraction was achieved at 50L of 1-octanol. However, the ana-lytes extracted in this volume displayed a poor chromatographicbehavior (peak tailing), which should be ascribed to the presenceof large por1-octanol wfor the analsuitable vol</p><p>3.1.2. ExtraThe extr</p><p>50min. Theof all the anTherefore, 2</p><p>3.1.3. IonicThe effe</p><p>In this studsolutionwa</p><p>2</p><p>3</p><p>4</p><p>5</p><p>6</p><p>7</p><p>8</p><p>9</p><p>10</p><p>11</p><p>Pea</p><p>k ar</p><p>ea (</p><p>x104</p><p>)</p><p>Fig. 3. Optimiume, 40L; io1300 rpm.</p><p>100806040200</p><p>4</p><p>5</p><p>6</p><p>7</p><p>8</p><p>9</p><p>10</p><p>Pea</p><p>k ar</p><p>ea (</p><p>x104</p><p>)</p><p>NaCl (mmol L-1 )</p><p> HB DB BP HMB</p><p>Fig. 4. Optimization of the ionic strength. Other conditions: extraction time, 20min;extraction solvent volume, 40L; pH of sample solution, 7.0; stirring speed,1300 rpm.</p><p>addition on the extraction. The results are demonstrated in Fig. 4.It can be observed that the salt addition has little inuence on theextraction performance. Therefore, no salt addition would be thebest choice.</p><p>SamppH v</p><p>ers, win F</p><p>7.0, towe</p><p>sed drobam toighe</p><p>ions,e res</p><p>Stirritatios frotion of 1-octanol in the HPLC samples. When 40L ofas used for the extraction, the chromatographic peaksytes were quite symmetric. Therefore, 40L would beume for the extraction solvent.</p><p>ction timeaction time was investigated in the range of 2 andresults are plotted in Fig. 3. It shows that the peak areasalytes are the highest at an extraction time of 20min.0min was selected as the optimal extraction time.</p><p>strengthct of salt addition in DLLME has been widely reported.y, 5100mmol L1 of sodium chloride in the samples separately evaluated todetermine the inuenceof salt</p><p> HB DB BP</p><p>3.1.4.The</p><p>UV ltplayed3.0 toingly. Hdecrealytes pfor thepH is hconditto thes</p><p>3.1.5.Agi</p><p>analyte</p><p>9</p><p>1050403020100</p><p>Time (min)</p><p> HMB</p><p>zation of the extraction time. Other conditions: extraction solvent vol-nic strength, 0mmol L1; pH of sample solution, 7.0; stirring speed,</p><p>2</p><p>0</p><p>1</p><p>2</p><p>3</p><p>4</p><p>5</p><p>6</p><p>7</p><p>8</p><p>Pea</p><p>k ar</p><p>ea (</p><p>x104</p><p>)</p><p>Fig. 5. Optimextraction so1300 rpm.le pH valuesalues, which can inuence the molecular status of theere investigated in the extraction. The results are dis-</p><p>ig. 5. It can be observed that as the pH increased fromhe peak areas for all of the analytes increased accord-ver, as the pH increased higher than 7.0, the peak areasramatically. When the pH was lower than 7.0, the ana-bly existed in their neutral forms, which was benecialdistribute into the organic phase. However, when ther than 7.0, probably the UV lters ionized in alkalinewhich was detrimental for their extraction. Accordingults, pH 7.0 should be the optimal pH for the extraction.</p><p>ng speedn is an effective way to accelerate the mass transfer ofm the aqueous solution to the extraction phase. In this</p><p> HB DB BP1210864</p><p>PH</p><p> HMB</p><p>ization of the pH value. Other conditions: extraction time, 20min;lvent volume, 40L; ionic strength, 0mmol L1; stirring speed,</p></li><li><p>1714 P.-P. Zhang et al. / Talanta 83 (2011) 17111715</p><p>0</p><p>2</p><p>4</p><p>6</p><p>8</p><p>10</p><p>12</p><p>Pea</p><p>k ar</p><p>ea (</p><p>x104</p><p>)</p><p> HB DB BP HMB</p><p>Fig. 6. Optimextraction solv7.0.</p><p>study, the sIt is foundefciency iagitation brdispersed wa result, enspeed. In thof the magextraction.</p><p>Based otions for th20min of exple pH at 7.</p><p>3.2. Method</p><p>A seriesdetections (formed toconditions.pure waterThe resultsmethod waconcentratiranges wer810,000ngtively. The rall the UVranged from</p><p>The repeby spikingtion of 80nbelow 4.7%</p><p>Table 2Linear range, r(RSDs) and en</p><p>Analyte L(</p><p>HB 8DB 7BP 8HMB 5</p><p>a Calculated</p><p>BP</p><p>HB</p><p>Abs</p><p>orba</p><p>nce </p><p>(AU</p><p>)</p><p>hromter dir1 wiconce</p><p>d. Hibtain</p><p>alys</p><p>proater stratethat ting tthes, thel SPEhe sratufor</p><p>d.est tcesstratiult is</p><p>analygmLnrich.1% fo.4% a140012001000800600400200</p><p>Stirring speed ( rpm)</p><p>ization of stirring speed. Other conditions: extraction time, 20min;ent volume, 40L; ionic strength, 0mmol L1; pH of sample solution,</p><p>tirring speed was investigated from 260 to 1300 rpm.that as the stirring speed increased, the extraction</p><p>mproved signicantly (as shown in Fig. 6). The fastoke up the 1-octanol into ne droplets, which highlyithin the aqueous solution to facilitate extraction. Ashanced extraction could be achieved at high stirringe present case, 1300 rpm is themaximumstirring speednetic stirrer. Therefore, this speed was used for the</p><p>n the above discussion, the optimal extraction condi-e proposed method were a stirring speed at 1300 rpm,traction time, 1-octanol as the extraction solvent, sam-00 and no salt addition.</p><p>evaluation</p><p>of experiments with regard to the linearity, limit ofLODs), enrichment factors and repeatability were per-validate the proposed method under the optimizedSample solutions (20mL) were prepared by spikingwith the UV lters at different concentration levels.obtained are listed in Table 2. The linearity of the</p><p>s evaluated using spiking water samples at differentons ranging from 5 to 20000ngmL1. The linearitye 820,000ngmL1 for HB, 720,000ngmL1 for DB,mL1 for BP and 520,000ngmL1 for HMB, respec-</p><p>0</p><p>Fig. 7. Clake wa80ngmLlters at</p><p>methowere o</p><p>3.3. An</p><p>Thelake wwas...</p></li></ul>