胡紅美,郭遠明,郝青,孫秀梅,金衍健,鐘志,張小軍(浙江省海洋水產(chǎn)研究所/浙江省海洋漁業(yè)資源可持續(xù)利用技術研究重點實驗室,浙江舟山316021)

自動液液萃取-分散固相萃取凈化-氣相色譜法測定水體中的多氯聯(lián)苯

胡紅美,郭遠明*,郝青,孫秀梅,金衍健,鐘志,張小軍
(浙江省海洋水產(chǎn)研究所/浙江省海洋漁業(yè)資源可持續(xù)利用技術研究重點實驗室,浙江舟山316021)

摘要為快速、準確監(jiān)測環(huán)境水體中多氯聯(lián)苯(polychlorinated biphenyls,PCBs)的含量,建立了一種自動液液萃取、分散固相萃取凈化、氣相色譜電子捕獲檢測法同時測定水體中7種PCBs的方法.樣品經(jīng)正己烷液液萃取后,只需在萃取濃縮液中加入固相吸附劑除雜便可達到凈化效果,并對分散固相萃取凈化過程中吸附劑的種類和用量進行了優(yōu)化.結(jié)果表明,7種PCBs在1.25～100μg/L質(zhì)量濃度范圍內(nèi)組分含量與峰面積呈線性相關,相關系數(shù)為0.999 0～0.999 8,檢測限為0.000 2～0.000 3μg/L.千島湖水和岱衢洋海域海水中7種PCBs不同濃度加標水平回收率分別為74%～105%和71%～107%,相對標準偏差分別為3.1%～6.2%和3.5%～5.9%(n=5).本方法簡單快速,高效,基體干擾小,靈敏度、準確度、精密度均滿足水體中PCBs的定量分析要求.

關鍵詞自動液液萃取;分散固相萃取凈化;氣相色譜電子捕獲檢測法;多氯聯(lián)苯;水體

浙江大學學報(農(nóng)業(yè)與生命科學版) 42(1):99～106,2016

Journal of Zhejiang University(Agric.&Life Sci.)

http://www.journals.zju.edu.cn/agr

E-mail:zdxbnsb@zju.edu.cn

第一作者聯(lián)系方式:胡紅美(http://orcid.org/0000-0003-3750-3755),E-mail:huhm@zju.edu.cn

URL:http://www.cnki.net/kcms/detail/33.1247.S.20160119.1930.014.html

Determination of polychlorinated biphenyls in water by gas chromatography-electron capture detector combined with automated liquid-liquid extraction and dispersive solid phase extraction clean-up.Journal of Zhejiang University(Agric.&Life Sci.),2016,42(1):99-106

HU Hongmei,GUO Yuanming*,HAO Qing,SUN Xiumei,JIN Yanjian,ZHONG Zhi,ZHANG Xiaojun (Marine Fishery Institute of Zhejiang Province/Key Laboratory of Sustainable Utilization of Technology Research for Fishery Resource of Zhejiang Province,Zhoushan 316021,Zhejiang,China)

Summary Polychlorinated biphenyls(PCBs)are a group of synthetic organic compounds and comprise a family of 209 possible congeners.PCBs are hazardous due to their persistence,hydrophobic character and toxic properties.Although they have been banned on a global scale since 1972,PCBs are still routinely found throughout the world and cause many ecotoxicological problems.Therefore,it is necessary to continue developing analytical methods for the analysis of PCBs in environmental samples.Analysis of PCBs in water is usually performed by gas chromatography(GC)or gas chromatography-mass spectrometry(GC-MS)combined with liquid-liquid extraction (LLE),solid phase extraction(SPE),solid phase disk extraction(SPDE),solid phase microextraction(SPME),headspace SPME(HS SPME),(magnetic)dispersive solid phase extraction(DSPE),dispersive liquid-liquid microextraction(DLLME)and membrane-assisted solvent extraction(MASE).Among these sample preparation methods,SPE,SPDE,SPME,and HSSPME usually suffer from high cost,sample carry-over,and time-decliningperformance.DLLME is easy to over-extraction and some matrix could be easily condensed.LLE as a reliable and simple method is often used for water sample pretreatment in large volumes.But after LLE,the extracts are usually required for further clean-up using concentrated sulfuric acid or SPE.(Magnetic)DSPE is quick,easy,cheap,effective,rugged and safe,but it is also subject to adsorbent.Besides,the extraction process is tedious,including dispersed,isolate,transfer,elute and even further purification.Therefore,the objective of this study was to develop an improved DSPE clean-up method to replace concentrated sulfuric acid or SPE after LLE,which needs less time and operation steps.

Now,a simple,rapid,efficient,sensitive,and low matrix interference method for determination of seven PCBs(including PCB28,PCB52,PCB101,PCB118,PCB153,PCB138,PCB180)in water samples using gas chromatography-electron capture detector(GC-ECD)combined with automated LLE and DSPE has been described.In the designed experiment,water samples were firstly extracted with n-hexane,and then the extracts were directly purified by a suitable adsorbent.The kinds and amounts of adsorbent were optimized.

Primary secondary amine(PSA)sorbent was chosen for DSPE purification,which could eliminate interferences to PCB28 and PCB52.But there were still some impurities to PCB52 and PCB28 by DSPE purification with C18as sorbent as well as concentrated sulfuric acid purification.It may be because PSA could effectively remove carbohydrates,fatty acids,organic acids,polyphenols,sugar and polar pigments on the objective compounds,while C18was mostly used to remove some non-polar disruptors such as fat and esters.By increasing the amount of PSA sorbent from 0 to 100 mg,the purify efficiency values increased significantly,and the recoveries of seven PCBs were almost invariant when the amount of sorbent ranged from 100 to 200 mg.As PSA could also adsorb n-hexane,increasing amount of PSA would result in a decrease of supernatant after centrifugation.Hence,100 mg PSA sorbent was used,at this point,good purify efficiency and satisfactory recoveries were both achieved.Furthermore,the present DSPE process only needed less than 5 min for dispersion and centrifugation.

The linearity of this method ranged from 1.25μg/L to 100μg/L,with correlation coefficients ranging between 0.999 0 and 0.999 8.The detection limits for seven PCBs were 0.000 2-0.000 3μg/L.The recoveries of spiked PCBs at different concentration levels in water samples of Qiandao Lake and seawater samples of Daiquyang sea area were 74%-105%,and 71%-107%,respectively,with relative standard deviations(RSDs)of 3.1%-6.2%,and 3.5%-5.9% (n=5),respectively.It was concluded that this method could be successfully applied for the determination of PCBs in water samples with good accuracy and precision.

Key words automated liquid-liquid extraction;dispersive solid phase extraction;gas chromatography-electron capture detector;polychlorinated biphenyls;water

多氯聯(lián)苯(polychlorinated biphenyls,PCBs)作為一類人工合成的氯代持久性有機污染物,迄今發(fā)現(xiàn)有209種異構(gòu)體,具有高毒性、長距離遷移性、環(huán)境持久性和生物蓄積性等特點[1 3],極易在水、大氣、土壤等環(huán)境介質(zhì)中殘留,并通過食物鏈蓄積于人和動物體中,對人類健康帶來巨大威脅,是2001年5月《斯德哥爾摩公約》12種優(yōu)先控制污染物之一[4-5].盡管從1972年開始,全球范圍內(nèi)要求逐漸停止使用和生產(chǎn)PCBs,但由于其持久性和疏水性等特性導致其在環(huán)境中殘留并積累.PCBs難溶于水,水中痕量PCBs污染經(jīng)常被人忽略,《地表水環(huán)境質(zhì)量標準》(GB 3838—2002)規(guī)定集中式生活飲用水地表水源地水中PCBs的含量不能超過2×10-5mg/L,因此亟須尋找一種簡單、快速而又準確的方法來定量分析水體中PCBs殘留.

目前,國內(nèi)外測定水體中多氯聯(lián)苯的分析方法有氣相色譜法、氣相色譜-質(zhì)譜法、高效液相色譜法、磁共振法、紅外光譜法、生物或化學傳感器法、酶聯(lián)免疫檢測法等,其中最常用的仍為氣相色譜法和氣相色譜-質(zhì)譜法.常用的前處理技術主要有液液萃取(liquid-liquid extraction,LLE)[6-9]、固相萃取(solid phase extraction,SPE)[10-13]、固相膜萃取(solid phase disk extraction,SPDE)[14]、固相微萃取(solid phase microextraction,SPME)[15-16]、頂空固相微萃取(headspace SPME,HS SPME)[17-18]、(磁性)分散固相萃取(dispersive solid phase extraction,DSPE)[19-24]、分散液液微萃取(dispersive liquid-liquid microextraction,DLLME)[25]、膜輔助溶劑萃取(membrane-assisted solvent extraction,MASE)[26]等.當使用LLE時,由于水體中存在一些雜質(zhì),常需結(jié)合濃硫酸磺化凈化[8 9]或SPE凈化[7 8]的1種或2種.當水樣直接采取SPE時,水樣流經(jīng)萃取柱時間較長,通常需要100 min,使用固相膜萃取雖顯著增加水樣流速,但萃取過程仍需萃取膜活化、上樣、淋洗、洗脫等過程,操作比較煩瑣.水樣直接采用SPME 或HS SPME時,萃取頭成本較高,萃取涂層易磨損,萃取后樣品需要解析,使用壽命較短,多次使用還存在交叉污染問題.DSPE具有快速、簡單、便宜、有效、可靠和安全的特點,已逐步應用到水體中各種有機污染物的檢測.目前,雖有文獻采用磁性納米材料或自制吸附劑直接分散固相萃取水體中多氯聯(lián)苯,但萃取過程需分散—吸附—分離—轉(zhuǎn)移—洗脫等步驟,操作較復雜,且有時萃取后還需結(jié)合濃硫酸磺化凈化.因此,尋找一種合適的固相吸附劑直接吸附雜質(zhì),且目標化合物仍然遺留在濃縮液中,離心分離后萃取濃縮液可以直接上機測試的分散固相萃取方法,將為水體中多氯聯(lián)苯前處理凈化技術提供新思路.

不同水體基體差別較大,前處理成為水樣中PCBs殘留分析的關鍵.本研究為縮短前處理時間,建立自動液液萃取、快速分散固相萃取凈化、氣相色譜電子捕獲檢測法(gas chromatography-electron capture detector,GC-ECD)測定不同基質(zhì)水體中7種“指示性PCB”單體(PCB28、PCB52、PCB101、PCB118、PCB153、PCB138、PCB180)含量,取得了比較滿意的效果,可作為進一步研究多氯聯(lián)苯的暴露水平和環(huán)境行為之參考.

1　材料與方法

1.1主要儀器和試劑

GC-450氣相色譜儀,購自美國Varian公司;配置電子捕獲檢測器(electron capture detector,ECD);Varian Star50C色譜工作站;Jipad-6XB垂直振蕩器,購自上海旌派儀器有限公司;MS2渦旋混合器,購自德國IKA公司;Centrifuge 5810高速離心機,購自德國Eppendorf公司;R-215旋轉(zhuǎn)真空蒸發(fā)儀,購自瑞士Büchi公司;N-丙基乙二胺吸附劑(primary secondary amine,PSA),粒徑50μm,購自上海安譜科學儀器有限公司;C18吸附劑,粒徑50 μm,購自上海安譜科學儀器有限公司.

7種多氯聯(lián)苯混合標準溶液,2.0 mg/L,SB 05-174—2008,購自農(nóng)業(yè)部環(huán)境保護科研監(jiān)測所;丙酮、正己烷(色譜純),購自國藥集團化學試劑有限公司;無水硫酸鈉(優(yōu)級純),購自國藥集團化學試劑有限公司,使用前550℃烘烤2 h.

7種多氯聯(lián)苯混合標準使用液(100μg/L):取0.5 m L的7種多氯聯(lián)苯混合標準溶液,用正己烷定容至10 m L,配制成100μg/L的混合標準使用液,于4℃儲存.

1.2色譜條件

CD-5MS毛細管氣相色譜柱(30 m×0.25 mm,0.25μm);進樣方式開始不分流進樣,0.75 min后分流比為50∶1;載氣為高純氮氣(99.999%);流速為2.0 mL/min;進樣口溫度為260℃;ECD檢測器溫度為300℃;程序升溫條件為柱初始溫度120℃,保持1.0 min,以10℃/min升至200℃,再以2℃/min升溫至240℃,最后以15℃/min升溫至270℃,保持1.0 min;總運行時間32 min,進樣體積為1μL.

1.3實驗方法

1.3.1水樣采集

分別采集杭州千島湖的湖水和岱衢洋海域的海水水樣,裝于4-L帶硅膠密封墊的棕色細口玻璃瓶中,然后用便攜式冷藏箱運回實驗室.

1.3.2樣品前處理

準確量取1 L待測水樣,置于2-L分液漏斗中,加入30 g氯化鈉(海水樣品不用加),分別用40 m L正己烷采用垂直振蕩器自動振蕩萃取2次,每次振蕩5 min,靜置分層,棄去水相,有機相經(jīng)無水硫酸鈉脫水,35℃旋轉(zhuǎn)蒸發(fā)至干,加入1 m L正己烷溶解,轉(zhuǎn)移至含100 mg PSA的具塞離心管中,渦旋30 s,6 000 r/min高速離心2 min,取1μL上清液進行上機測試.

2　結(jié)果與討論

2.1萃取方式的選擇

水樣直接固相萃取或固相膜萃取雖然可以富集大體積水樣,但固相萃取柱/膜的活化、吸附、解吸過程耗時較長,當水樣含較多懸浮物時容易堵塞萃取裝置,萃取前需過濾水樣,增加前處理時間,容易造成損失,且商品化萃取柱填充材料以及膜介質(zhì)材料中的干擾物質(zhì)可能會隨洗脫劑洗脫下來影響測定.固相微萃取頭成本較高,萃取涂層易磨損,萃取后樣品需要解析,使用壽命較短,多次使用還存在交叉污染問題,重現(xiàn)性也較差.水樣直接分散固相萃取也需分散、吸附、分離、解吸等操作,且找到一種合適的吸附材料是萃取效率的關鍵.目前報道較多的是使用磁性納米材料作為吸附劑,以便于磁性分離.ZENG 等[20-21]設計了一種基于磁性納米管材料的分散固相萃取方法,萃取后還需濃硫酸凈化,且磁性納米管材料需實驗室自制備.液液萃取法則具有操作簡單,成本低,回收率高等優(yōu)點,尤其在批量化水樣前處理時,仍是目前實驗室分析的首選[27].經(jīng)過綜合考慮,決定選擇垂直振蕩器實現(xiàn)自動液液萃取水體中的多氯聯(lián)苯.

2.2凈化方式的選擇

由于本實驗選擇自動液液萃取法萃取水體中多氯聯(lián)苯,萃取液通常需要凈化.文獻報道最多的是濃硫酸凈化或固相萃取凈化.濃硫酸可破壞活性強、穩(wěn)定性差的有機化合物,經(jīng)研究表明濃硫酸凈化法可以除去大多數(shù)的干擾雜質(zhì),但始終有雜質(zhì)對PCB52產(chǎn)生干擾,且有時對PCB28也產(chǎn)生干擾.雖然固相萃取法凈化效果也較好,但操作復雜,需要進行萃取柱活化—上樣—淋洗—洗脫等過程,耗時較長,不適合批量化樣品處理.本研究采用分散固相萃取凈化法,只需在萃取濃縮液中加入適量合適吸附劑吸附雜質(zhì),便可達到凈化目的.整個分散固相萃取凈化過程最多只需要5 min,而常規(guī)固相萃取通常需要50 min,大大縮短前處理時間.

2.3固相吸附劑種類和用量的選擇

比較了100 mg PSA吸附劑和100 mg C18吸附劑的凈化效果(圖1).結(jié)果表明,C18吸附劑對PCB28、PCB52附近雜質(zhì)凈化基本沒效果,PSA吸附劑能有效消除雜質(zhì)對PCB28、PCB52檢測的干擾.這可能是因為PSA吸附劑能有效除去影響目標物檢測的碳水化合物、脂肪酸、有機酸、酚類、糖類以及一些極性色素的干擾,C18吸附劑主要用于去除脂肪和酯類等非極性干擾物,而對于水體中多氯聯(lián)苯檢測,雜質(zhì)主要干擾PCB28、PCB52.接著,考察PSA吸附劑含量(0～200 mg)對凈化效果的影響.結(jié)果(圖2)表明,隨著PSA吸附劑用量的增加,凈化效果有所增加,當達到一定量后,即使吸附劑增加,但回收率變化不大.由于PSA吸附劑會吸附一定的正己烷,PSA劑量增加,離心分離后,上清液減少,最終選擇100 mg,此時既能達到較好的凈化效果,又能保證較滿意的回收率.另外,多次收集廢棄PSA吸附劑,使用合適的有機溶劑可以解析被PSA吸附的雜質(zhì),從而實現(xiàn)PSA的集中回收利用,這不僅降低了實驗成本,也減少了廢棄固相吸附劑帶來的環(huán)境問題.這方面的研究將在今后工作中開展.

2.4方法評價

2.4.1方法的線性范圍及檢出限

將已配制的1.25、2.5、5、10、50、100μg/L 6個質(zhì)量濃度梯度的標準系列,按樣品分析相同的色譜條件進行GC-ECD分析.用外標法繪制出濃度-峰面積標準曲線.7種多氯聯(lián)苯在1.25～100μg/L范圍內(nèi)呈良好線性關系,相關系數(shù)為0.999 0～0.999 8.各組分的線性回歸方程、線性范圍和相關系數(shù)見表1,根據(jù)3倍信噪比測得7種多氯聯(lián)苯的檢出限為0.000 2～0.000 3μg/L.7種多氯聯(lián)苯的標準氣相色譜譜圖見圖3.

2.4.2實際樣品分析、方法的精密度和回收率

分別準確量取千島湖采集的6個湖水樣品(樣品1至樣品6)和岱衢洋海域12個采樣點采集的海水樣品(樣品7至樣品18)1 L,進行3次平行測定,結(jié)果均未檢出7種多氯聯(lián)苯.在其中2個樣品(樣品1和樣品7)中分別加入12.5μg/L、100μg/L和1 000μL 的100μg/L多氯聯(lián)苯混合標準使用液,配制成低(0.001 25μg/L),中(0.01μg/L)和高(0.1μg/L)3種質(zhì)量濃度的標樣,分別進行5次重復測定.結(jié)果(表2,3)表明,樣品1和樣品7中7種PCBs回收率范圍分別為74%～105%和71%～107%,RSDs范圍分別為3.1%～6.2%和3.5%～5.9%,準確度和精密度均滿足分析方法要求.2種不同基質(zhì)樣品回收率差別不大,圖4為樣品7和加標樣品7的氣相色譜圖.結(jié)果表明,經(jīng)過PSA吸附劑快速分散固相萃取后,雜質(zhì)對目標化合物基本無干擾峰.

3　結(jié)論

采用正己烷自動液液萃取提取水體中的多氯聯(lián)苯,再采用分散固相萃取快速凈化后,進行GC-ECD分析.實驗結(jié)果表明,將萃取濃縮液直接用固相吸附劑吸附雜質(zhì)實現(xiàn)分散固相萃取凈化,與水樣直接分散萃取或固相萃取相比,只需分散、吸附,無需富集、洗脫步驟.該方法簡單、快速、靈敏度高、重現(xiàn)性好,回收率令人滿意,可以實現(xiàn)批量化處理樣品,值得大力推廣,對水質(zhì)環(huán)境中多氯聯(lián)苯的檢測具有重要的指導意義.

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收稿日期(Received):2015-07-10;接受日期(Accepted):2015-08-27;網(wǎng)絡出版日期(Published online):2016-01-19

*通信作者(

Corresponding author):郭遠明(http://orcid.org/0000-0003-2443-3890),E-mail:yuanming_guo@126.com

基金項目:國家自然科學基金(21407127);浙江省自然科學基金(LQ13C200004;LQ14B070002).

DOI:10.3785/j.issn.1008-9209.2015.07.102

中圖分類號O 657.7;R 123.1;X 832

文獻標志碼A