吳少尉，胡 航

(湖北民族學(xué)院 化學(xué)與環(huán)境工程學(xué)院，湖北 恩施 445000)

電熱蒸發(fā)電感耦合等離子體原子發(fā)射光譜/質(zhì)譜(ETV-ICP-OES/MS)分析技術(shù)中，電熱蒸發(fā)(ETV)作為固/液體共同適用的微量進(jìn)樣裝置，可以與各種傳統(tǒng)的和新型的微型化分離預(yù)富集技術(shù)聯(lián)用.使ETV-ICP-OES/MS聯(lián)用檢測(cè)技術(shù)在痕量/超痕量元素分析及元素形態(tài)分析中發(fā)揮重要作用.削弱甚至克服了以下困難：樣品中目標(biāo)元素的濃度極低，其各種不同形態(tài)的濃度則更低難檢測(cè)；進(jìn)樣效率低，分析的靈敏度及準(zhǔn)確性不高；大量共存基體成分所產(chǎn)生的干擾導(dǎo)致不準(zhǔn)確的分析結(jié)果.建立一些分離基體、富集目標(biāo)元素、簡(jiǎn)便快捷且環(huán)境友好的微型化樣品前處理技術(shù)，是當(dāng)前ETV-ICP-OES/MS應(yīng)用研究中的重點(diǎn)和熱點(diǎn)之一.本文在ICP-OES/MS中的進(jìn)樣技術(shù)[1]之后，從傳統(tǒng)的和新型的分離預(yù)富集技術(shù)延續(xù)評(píng)論ETV-ICP-OES/MS中的分離預(yù)富集技術(shù)，以期就ETV-ICP-OES/MS研究給讀者以及時(shí)捕捉前沿研究信息的目的.

1 傳統(tǒng)的分離預(yù)富集技術(shù)

1.1 液-液萃取(Liquid-liquid extraction,LLE)

常規(guī)LLE的缺點(diǎn)是需要消耗大量的有機(jī)溶劑，環(huán)境欠友好，操作過程中有時(shí)產(chǎn)生乳化現(xiàn)象，費(fèi)力費(fèi)時(shí).可是LLE技術(shù)成本低，無需特殊裝置，操作簡(jiǎn)便，重現(xiàn)性好，樣品容量大，目前在一些樣品[2,3]分析中仍然還有應(yīng)用.協(xié)同萃取(synergic extraction)是使用兩種或兩種以上萃取劑的混合物做萃取相的一種特殊的LLE技術(shù)，加入的第二種萃取劑(協(xié)萃劑)對(duì)萃取有增強(qiáng)作用，提高了萃取效率，被萃取物可得到更高的富集倍數(shù).協(xié)同效應(yīng)的性質(zhì)和程度主要取決于協(xié)萃劑本身的性質(zhì)，以及金屬離子和螯合劑的性質(zhì).混配絡(luò)合物的形成被認(rèn)為是產(chǎn)生協(xié)同萃取效應(yīng)、提高萃取效率的主要原因.如果一個(gè)中性給予體分子(協(xié)萃劑)從萃取螯合物中置換了水分子，則會(huì)降低該絡(luò)合物的親水性而有利于萃取.Matsubayashi等[4]采用噻吩甲酰三氟丙酮(TTA)和安息香酸(HB)實(shí)現(xiàn)了對(duì)稀土元素(REEs) 的協(xié)同萃取，發(fā)現(xiàn)隨著原子序數(shù)的增大，由同樣數(shù)目的水分子和稀土離子帶來的熵變逐步占主導(dǎo)地位，從而影響絡(luò)合反應(yīng)，使絡(luò)合物的二次穩(wěn)定常數(shù)減小，導(dǎo)致協(xié)同萃取效應(yīng)的逐步減弱.這個(gè)發(fā)現(xiàn)從理論上解釋了協(xié)同萃取REEs時(shí)的變化規(guī)律，為更好的利用協(xié)同萃取來分析REEs奠定了基礎(chǔ).Yin[5]和Xiong[6]等利用協(xié)同萃取建立了ETV-ICP-MS測(cè)定環(huán)境樣品中稀土元素的新方法.在相比不超過10時(shí)，均可得到5～7倍的富集.

1.2 固相萃取(Solid phase extraction,SPE)

SPE是通過一定粒徑的多孔固體材料選擇性地吸附溶液中的被測(cè)物質(zhì)，即目標(biāo)分析物被定量吸附后，再用體積較小的一種溶劑洗脫或用物理熱解吸法解吸被萃取物，在此過程中達(dá)到分離基體、富集待測(cè)物質(zhì)的目的，最后選用適當(dāng)?shù)臋z測(cè)方法進(jìn)行分析測(cè)定.若難以洗脫而吸附材料廉價(jià)易得，也可以不經(jīng)洗脫[1,7]直接將萃取待測(cè)物的固定相引入ETV中，設(shè)定合理的升溫程序用ETV-ICP-OES/MS進(jìn)行檢測(cè).與傳統(tǒng)的LLE相比，固相萃取具有以下優(yōu)點(diǎn)：①較理想的回收率(70%～100%)，富集倍數(shù)高；②無相分離操作，處理試樣體積彈性大，易于收集目標(biāo)組分；③可現(xiàn)場(chǎng)采集，并分離/富集待測(cè)組分；④將試樣脫鹽，便于試樣的儲(chǔ)存和運(yùn)輸；⑤可供選擇的固相萃取材料種類繁多，應(yīng)用范圍廣；⑥避免使用有機(jī)溶劑，環(huán)境友好，操作簡(jiǎn)單，快速、易于實(shí)現(xiàn)自動(dòng)化.SPE與ETV-ICP-OES/MS檢測(cè)儀器的聯(lián)用分析[8，9]已有很多報(bào)道，Valerie[10]對(duì)SPE原理、操作和應(yīng)用等方面作了較為全面的評(píng)述.目前，對(duì)于SPE的研究主要集中在新型固相萃取材料的開發(fā)和萃取裝置的微型化兩方面.SPE柱材料的選擇一般由分析目的和分析對(duì)象所決定，針對(duì)性的選擇合適的萃取材料是成功建立一個(gè)分析方法的關(guān)鍵所在.目前，一些新型的功能吸附材料，如無機(jī)納米金屬氧化物[11]、碳納米管[12]、介孔材料[13]、離子印跡材料[14，15]等，被不斷開發(fā)出來并成功用于SPE及痕量元素分析.

表1 電熱蒸發(fā)等離子體原子光/質(zhì)譜中的樣品前處理技術(shù)

2 微型化的樣品前處理技術(shù)

作為一種微量進(jìn)樣技術(shù)，ETV與微型化的樣品前處理技術(shù)聯(lián)用是一種完美的微微結(jié)合，可使ETV-ICP-OES/MS 發(fā)揮出巨大的分析潛能，分析應(yīng)用范圍得到更進(jìn)一步的拓寬.這與目前樣品前處理技術(shù)微型化、綠色化的發(fā)展趨勢(shì)相吻合.表1列出了ETV-ICP-OES/MS與各種分離富集技術(shù)聯(lián)用的分析應(yīng)用情況.下面將對(duì)一些微型化的樣品前處理技術(shù)進(jìn)行逐一介紹.

2.1 液相微萃取(Liquid-phase microextraction,LPME)

針對(duì)LLE技術(shù)的缺點(diǎn)，1996年Jeannot和Cantwell[30]發(fā)展和建立了一種綠色環(huán)保的新型樣品前處理技術(shù)—LPME.與傳統(tǒng)LLE技術(shù)相比，它只需要幾十微升甚至幾微升的有機(jī)溶劑，富集倍數(shù)高，特別適用于環(huán)境樣品中痕量、超痕量污染物的測(cè)定.同時(shí)，該技術(shù)集萃取、濃縮和進(jìn)樣于一體，靈敏度高，易于實(shí)現(xiàn)與高靈敏的檢測(cè)技術(shù)聯(lián)用.迄今為止，已經(jīng)發(fā)展了3種液相微萃取的萃取方式：直接單滴液相微萃取(direct single drop microextraction,Direct-SDME)、頂空單滴液相微萃取(headspace single drop microextraction,HS-SDME)和中空纖維膜液相微萃取(hollow fiber liquid phase Microextraction,HF-LPME).

圖1 循環(huán)單滴微萃取示意圖

圖2 中空纖維液相微萃取示意圖

Direct-SDME方式是利用懸掛在微量進(jìn)樣器針尖或聚四氟乙烯棒端的有機(jī)溶劑液滴浸沒在樣品溶液中對(duì)分析物進(jìn)行直接萃取.Liu和Lee[31]報(bào)道了一種名為循環(huán)流微萃取的方法，對(duì)5種硝基苯化合物和6種氯苯化合物進(jìn)行了分析，實(shí)現(xiàn)了260～1 600倍的高倍富集.吳英亮等[32]對(duì)該文獻(xiàn)提出的裝置進(jìn)行了改進(jìn)，將同一個(gè)裝置用于連續(xù)流和循環(huán)流兩種模式的萃取(如圖1所示)，首次將這種微萃取技術(shù)應(yīng)用于無機(jī)物的分離富集中，建立了微滴溶劑萃取-低溫ETV-ICP-OES檢測(cè)超痕量La的新方法.Xia等將揮發(fā)性小、環(huán)境友好的離子液體用作萃取單滴[33]，用ETV-ICP-MS測(cè)定了生物和環(huán)境樣品中痕量有毒元素Pb、Hg、Cd.

將有機(jī)萃取液滴懸于樣品溶液上部空間而進(jìn)行萃取的方法，被稱為HS-SDME[34]，這種萃取方式對(duì)揮發(fā)性的目標(biāo)分析物有較好的萃取作用.Zhang等[35]則直接使用比有機(jī)溶劑揮發(fā)性小的水作為溶劑，對(duì)試樣中的揮發(fā)性離子型化合物進(jìn)行了很好地分離富集.

基于中空纖維膜[36]的液相微萃取技術(shù)的建立，很好地避免了HS-SDME方式中液滴穩(wěn)定性不好的問題，如圖2所示.目標(biāo)分析物通過不流動(dòng)的、充滿于中空纖維膜多孔結(jié)構(gòu)中的薄層有機(jī)溶劑，從水相樣品中被萃取出來，然后進(jìn)入中空纖維膜內(nèi)腔的接受溶液中，最后則可直接注入GC、HPLC、CE或ETV-ICP-OES/MS分析儀器中進(jìn)行檢測(cè).

2.2 濁點(diǎn)萃取和分散相液相微萃取(Cloud point extraction,CPE and dispersive liquid-liquid microextraction,DLLME)

CPE是以中性表面活性劑膠束水溶液的溶解性和濁點(diǎn)現(xiàn)象為基礎(chǔ)[37，38]，通過改變體系溫度引發(fā)相分離，將疏水性物質(zhì)與親水性物質(zhì)分離.該技術(shù)不使用揮發(fā)性有機(jī)溶劑，是一種環(huán)境友好的液相微萃取技術(shù).如表1所示，CPE技術(shù)與ETV-ICP-OES/MS聯(lián)用在痕量元素測(cè)定及元素形態(tài)分析中已經(jīng)得到了廣泛的應(yīng)用，主要集中在痕量金屬離子的分離/預(yù)富集和痕量元素的形態(tài)分析[39]以及作為CE與HPLC分離之前的一種預(yù)濃縮手段[40,41].其操作方式也由傳統(tǒng)的離線操作朝向在線操作[42]發(fā)展.

DLLME[43]是2006年出現(xiàn)的一種液相微萃取模式.這種微萃取的樣品前處理方法起源于HLLE和CPE，是基于3種溶劑成分共存的體系，通過離心作用誘導(dǎo)相分離，使分析物進(jìn)入第三相，然后將小體積的萃取相引入檢測(cè)儀器中進(jìn)行分析.在DLLME中，通過注射器將萃取溶劑和分散溶劑的混合物快速的注入到樣品溶液中，水相溶液即刻變得渾濁，離心之后溶液分為兩相，一相為澄清的水相溶液，另一相為微滴狀的有機(jī)相.與其它模式的液相微萃取相比，DLLME操作簡(jiǎn)便，重現(xiàn)性好，更重要的是DLLME適合批量操作，萃取動(dòng)力學(xué)快，在幾秒鐘之內(nèi)即可完成平衡萃取，節(jié)省了分析時(shí)間.DLLME技術(shù)大多用于對(duì)有機(jī)物的分離富集方面，而其在無機(jī)物分析中的應(yīng)用相對(duì)較少[44,45].

2.3 固相微萃取(Solid phase microextraction，SPME)

20世紀(jì)90年代，Pawliszyn等[46]研發(fā)出了一種集樣品預(yù)處理和進(jìn)樣于一體的SPME技術(shù).SPME是一種基于氣固吸附和液固吸附平衡原理的分離富集方法，利用物質(zhì)對(duì)活性固體表面(熔融石英纖維表面的涂層)的吸附親合力不同而達(dá)到分離預(yù)富集的目的.它既有固相萃取操作簡(jiǎn)便、成本低、避免使用有機(jī)溶劑的優(yōu)點(diǎn)，又克服了吸附劑孔道易堵塞的缺點(diǎn).此外，SPME裝置攜帶方便，特別適合于現(xiàn)場(chǎng)分析，也易于實(shí)現(xiàn)自動(dòng)化.SPME自1993年由Supelco公司商品化以來，已有不同類型的商品化萃取頭可供選擇，并被廣泛的應(yīng)用于環(huán)境、生物技術(shù)、食品、醫(yī)藥等眾多分析領(lǐng)域.

SPME方法是通過萃取頭上的固相吸附劑涂層對(duì)樣品中的待測(cè)物進(jìn)行萃取和預(yù)富集，分為直接法、頂空法和膜保護(hù)3種操作方式：直接SPME法是將SPME纖維頭直接插入水相或暴露于氣體樣品中進(jìn)行萃取的方法.在樣品充分?jǐn)嚢璧那疤嵯拢胶馑钑r(shí)間由待測(cè)物在涂層中的擴(kuò)散速率決定；頂空SPME法是將SPME萃取頭置于試樣溶液的上部空間進(jìn)行萃取.待測(cè)物在試樣基質(zhì)、液上空間、纖維涂層這三相中的化學(xué)勢(shì)是推動(dòng)待測(cè)物從基質(zhì)進(jìn)入纖維涂層的驅(qū)動(dòng)力，而這種驅(qū)動(dòng)力可以通過不斷攪拌水溶液試樣來增強(qiáng).通常，化合物氣態(tài)下的擴(kuò)散系數(shù)比其液態(tài)下的擴(kuò)散系數(shù)至少大10 000多倍，因而揮發(fā)性物質(zhì)其頂空濃度要大于其液相濃度.在相同的恒溫?cái)嚢钘l件下，對(duì)于液相中的揮發(fā)性物質(zhì)，頂空SPME達(dá)到平衡的時(shí)間較直接SPME短；膜保護(hù)SPME法是通過一個(gè)選擇性的高分子材料膜將試樣與萃取頭分離，以實(shí)現(xiàn)間接萃取.膜的作用是保護(hù)萃取頭不被基質(zhì)污染，同時(shí)提高萃取的選擇性.在這種萃取方式中，由于待測(cè)物在達(dá)到萃取頭涂層之前必須擴(kuò)散通過膜，因此萃取速度比直接SPME慢.采用較薄的保護(hù)膜和提高萃取溫度可以縮短萃取時(shí)間.在實(shí)際分析應(yīng)用中選擇何種萃取方式應(yīng)根據(jù)樣品基體，分析物揮發(fā)性和它與基體的親合力而定.SPME與GC的聯(lián)用是研究得最早也是目前發(fā)展得最成熟的技術(shù)[47]，SPME也被應(yīng)用到元素形態(tài)分析[48]中.

圖3 固相微萃取示意圖

2.4 注射器微萃取(Microextraction in packed syringe，MEPS)

在固相萃取以及SPME研究中，醫(yī)用注射器可方便地用作吸附材料的填充柱并易于靈活推拉抽提溶液，成本低廉而且操作方便.Akman等[49]將Dowex HCR cationic型交換樹脂作為吸附材料填充在一個(gè)圓盤中，再套接到塑料注射器針筒前端，這種萃取裝置被用來分離富集海水樣品中的Pb和Cd，使用2.5 mol·L-1的鹽酸對(duì)保留在萃取柱上的Pb和Cd進(jìn)行洗脫，洗脫液直接引入FAAS進(jìn)行檢測(cè).方法簡(jiǎn)便快速，污染小，適用性強(qiáng).Akman等在后續(xù)研究[50]中，把一填裝吸附劑的小微柱套接到注射器的前端，在一定程度上減小了死體積.若使其進(jìn)一步微型化，這種方式可作為常規(guī)微柱分離富集技術(shù)的一種延伸.與其它固相萃取技術(shù)一樣，MEPS吸附材料性能的開發(fā)及其裝置的進(jìn)一步微型化是其發(fā)展的主要方向.瑞典分析家Abdel-Rehim Mohamed等[51]將MEPS裝置微型化：把微米級(jí)粒徑的固相吸附材料1 mg填充在一個(gè)微量注射器(100～250 μL)中當(dāng)作吸附床，如圖3所示，先后經(jīng)過采樣、清洗、洗脫、進(jìn)樣4個(gè)階段，接著注進(jìn)色譜儀進(jìn)行分析，對(duì)色譜儀進(jìn)樣口無需做任何改動(dòng).在采樣階段可以重復(fù)多次抽提來增加富集倍數(shù).整個(gè)過程基本實(shí)現(xiàn)在線自動(dòng)化，這個(gè)裝置使用吸附劑少，沖洗變得更容易.他們把這種微型化前處理技術(shù)命名為注射器微萃取.其洗脫劑的消耗量?jī)H為幾十微升，環(huán)境友好，簡(jiǎn)便易用.MEPS被成功用于血漿樣品中的麻醉劑，羅哌卡因及其代謝物[52，53]的前處理.

同傳統(tǒng)的SPME方法相比，MEPS分析速度更快,萃取效率更高，操作簡(jiǎn)便而且可以實(shí)現(xiàn)完全自動(dòng)化.另外，對(duì)于基體復(fù)雜的樣品比如血漿、尿樣等，MEPS抗基體干擾的能力更強(qiáng).

2.5 毛細(xì)管微萃取(Capillary microextraction，CME)

受氣相色譜本身的限制，SPME與GC的聯(lián)用技術(shù)不適合分析熱不穩(wěn)定的物質(zhì)和極性大、揮發(fā)性差的物質(zhì).SPME與HPLC的聯(lián)用可很好的解決上述問題.SPME與HPLC成功聯(lián)用的關(guān)鍵是接口的選擇，早期的SPME-LC聯(lián)用的接口只能采用手動(dòng)進(jìn)樣器與HPLC接口完成進(jìn)樣.

為了解決這一實(shí)際問題，1997年，Eisert和Pawliszyn[54]等率先提出了管內(nèi)固相微萃取(in tube solid phase micoextraction)的思想，并將其與HPLC聯(lián)用，實(shí)現(xiàn)了在管內(nèi)的SPME-HPLC的自動(dòng)化.后來，Malik[55]課題組又將管內(nèi)固相微萃取稱為毛細(xì)管固相微萃取(capillary solid phase microextraction)或毛細(xì)管微萃取.CME是將內(nèi)壁涂有固定相的GC毛細(xì)管柱用于樣品萃取，并與商品化HPLC自動(dòng)進(jìn)樣器相連，無需使用特殊的接口進(jìn)行解吸，實(shí)現(xiàn)了SPME與LC聯(lián)用的自動(dòng)化；同時(shí)，CME還克服了纖維固相微萃取(fiber SPME)的涂層在極性大的有機(jī)溶劑中容易發(fā)生膨脹、脫落和溶解等缺點(diǎn).與傳統(tǒng)外涂萃取針的固相微萃取法(fiber SPME)相比，CME的萃取涂層是涂附在毛細(xì)管內(nèi)壁的，所以萃取的化合物被富集在毛細(xì)管的內(nèi)壁.因CME使用細(xì)徑毛細(xì)管對(duì)樣品進(jìn)行萃取，為了防止柱和流路的堵塞，必須在萃取前除去樣品中的顆粒物，受此限制，CME較適合于潔凈水樣的分析.而Fiber SPME則可通過頂空萃取消除樣品中顆粒物的影響，還可在直接萃取后用水沖洗以清除纖維表面的顆粒物，因此，可以分析基體相對(duì)復(fù)雜的樣品，但是萃取纖維頭易發(fā)生斷裂，且萃取涂層易在攪動(dòng)中被破壞.

目前，CME常用的萃取柱是商品化的氣相毛細(xì)管色譜柱，其萃取涂層為一層色譜固定相，由于種類有限，選擇性較差，其應(yīng)用在一定程度上受到限制.因此，新萃取涂層材料的研制和出現(xiàn)大大推動(dòng)了CME技術(shù)的發(fā)展.2000年，Pawliszyn[56]研究小組將聚吡咯(PPY)通過化學(xué)聚合的方法對(duì)毛細(xì)管內(nèi)壁進(jìn)行修飾，并用自動(dòng)in-tube SPME與LC-MS聯(lián)用的方法分析了血清和尿液中的鹽酸醋丁洛爾類藥物；他們還將其與LC-ESI-MS聯(lián)用，成功的實(shí)現(xiàn)了水樣和生物標(biāo)樣中有機(jī)砷形態(tài)的分析[57].將鍵合了TiO2-PDMS的溶膠-凝膠涂層[58]的毛細(xì)管柱用于水樣中烷基苯、酮和多環(huán)芳烴的萃取，由于該涂層是通過化學(xué)鍵合的方式與毛細(xì)管內(nèi)表面鍵合的，具有好的熱穩(wěn)定性和溶劑穩(wěn)定性，并且在高pH值環(huán)境下化學(xué)穩(wěn)定性仍較好.此外，CME技術(shù)在痕量元素及其形態(tài)分析方面也有應(yīng)用：Wu等[59]用涂有多孔的二乙烯基苯聚合物固定相的商品化的Supel-Q PLOT毛細(xì)管柱直接萃取環(huán)境樣品沉積物中的三丁基錫化合物，用HPLC-ES-MS方法對(duì)其進(jìn)行檢測(cè)和表征，方法的檢出限為0.05 ng·mL-1.利用3-氨基丙基三甲氧基硅烷(APTMS)涂層毛細(xì)管萃取消除了ArCl+對(duì)ICP-MS測(cè)定砷的干擾[60].利用甲基丙烯酸[61]修飾的毛細(xì)管在pH大于7時(shí)可定量保留無機(jī)鉛而不保留有機(jī)鉛(三乙基鉛)的特性，建立了CME-ICP-MS在線檢測(cè)分析鉛形態(tài)的方法，方法對(duì)三乙基鉛和無機(jī)鉛的檢出限分別是90 ng·L-1和200 ng·L-1.胡斌教授課題組[23，62，63]采用溶膠-凝膠技術(shù)先后制備了ZrO2和有序介孔TiO2以及有序介孔Al2O3涂層毛細(xì)管柱，建立了流動(dòng)注射在線CME-ICP-MS分析環(huán)境和生物樣品中痕量/超痕量元素的新方法，實(shí)驗(yàn)結(jié)果表明有序介孔涂層由于具有的大比表面積、高的孔隙率和孔道排列長(zhǎng)程有序等特點(diǎn)，對(duì)金屬離子具有高效的吸附萃取率.另外，2-氨基乙基-3-氨基丙基三乙氧基硅烷(AAPTS)改性硅膠[25]涂層毛細(xì)管雙柱被成功用于鋁的組形態(tài)研究.這些應(yīng)用實(shí)例表明，開發(fā)和研制高選擇性的和高萃取效率的涂層材料是毛細(xì)管微萃取技術(shù)的一個(gè)重要的發(fā)展方向.

管壁涂漬(鍵合)的毛細(xì)管微萃取柱通常存在涂層不夠穩(wěn)定、傳質(zhì)阻力大、吸附容量小等缺點(diǎn).為了克服上述缺點(diǎn)，人們開發(fā)出了毛細(xì)管整體柱，在一定程度上有效克服了上述缺點(diǎn)，具有制備簡(jiǎn)單、滲透性好、傳質(zhì)速率高等優(yōu)點(diǎn).Shintani等[64]將C18改性后的硅膠整體柱用于烷基酚類和稠環(huán)芳烴的分析.馮鈺锜課題組將有機(jī)聚合物引入到CME中，制備了聚(丙稀酰胺-乙烯基吡咯)[65,66]毛細(xì)管整體柱，并已用于有機(jī)和無機(jī)物的前處理上.他們還制備了聚(甲基丙稀酸-乙烯基乙二醇二甲基丙烯酸脂)[67,68]毛細(xì)管整體柱用于血漿中喜樹堿和奶粉中五種抗菌磺胺類藥物的前處理及測(cè)定.研究表明，這些毛細(xì)管整體柱具有高的萃取效率以及較好的生物相容性.此外，分子印跡技術(shù)、介孔材料等制備技術(shù)的發(fā)展也拓展了CME涂層制備及應(yīng)用新前景，使得CME技術(shù)具有更大的發(fā)展空間.

3 ETV-ICP-OES/MS聯(lián)用技術(shù)及形態(tài)分析

環(huán)境、醫(yī)藥、生命科學(xué)的迅速發(fā)展對(duì)分析方法提出了越來越高的要求：不僅要提供分析對(duì)象中元素的總含量, 還要提供元素的價(jià)態(tài)、化學(xué)形態(tài)及其遷移轉(zhuǎn)化等信息.由于ETV-ICP-OES/MS對(duì)元素形態(tài)或價(jià)態(tài)不具備選擇性，使ETV-ICP-OES/MS用于元素形態(tài)分析面臨著更大的挑戰(zhàn).

基于不同物質(zhì)的揮發(fā)性差異，可以設(shè)置不同的蒸發(fā)溫度使不同形態(tài)發(fā)生分離，所以通過控制ETV的升溫程序，或者借助合適的化學(xué)改進(jìn)劑，用ETV-ICP-OES/MS進(jìn)行元素形態(tài)分析是有一定可行性的.Gelaude等[69]將生物樣品直接引入ETV-ICP -MS，利用甲基汞和無機(jī)汞的揮發(fā)性差異，在150～200℃之間蒸發(fā)出甲基汞，在400～700℃之間蒸發(fā)出無機(jī)汞，實(shí)現(xiàn)了汞的形態(tài)分析.Hassler等[70]使用ETV-ICP -OES，在1250～2000℃蒸發(fā)出結(jié)合態(tài)鋁，而在2000～2450℃之間蒸發(fā)出晶格態(tài)鋁，實(shí)現(xiàn)了燒結(jié)碳化硅材料中鋁的形態(tài)分析.利用不同硼化合物的揮發(fā)性差異，使用四甲基氫氧化銨做ETV中的化學(xué)改進(jìn)劑，Okamoto等[71,72]實(shí)現(xiàn)了以ETV-ICP- OES/MS對(duì)生物和鋼樣品中硼的形態(tài)分析.

如前所述，為了達(dá)到形態(tài)分析的目的，發(fā)展由高效分離技術(shù)和高靈敏度光譜/質(zhì)譜檢測(cè)相結(jié)合的聯(lián)用技術(shù)是實(shí)現(xiàn)復(fù)雜樣品中元素形態(tài)分析的最有效途徑.在眾多的分離技術(shù)中，高選擇性、高效的色譜(高效液相色譜、氣相色譜、超臨界流體色譜)技術(shù)和毛細(xì)管電泳分離技術(shù)與ICP-OES/MS聯(lián)用是元素形態(tài)分析中首選的、也是當(dāng)前應(yīng)用最多的形態(tài)分析方法，體現(xiàn)了高選擇性分離與高靈敏度檢測(cè)的完美結(jié)合.胡斌等[73]在這一領(lǐng)域撰寫了全面詳細(xì)的專著，法國(guó)分析化學(xué)家Szpunar[74]對(duì)HPLC-ICP-OES/MS在元素形態(tài)分析方面的應(yīng)用進(jìn)行了全面完整的評(píng)論.近年來，對(duì)于色譜分離技術(shù)與ICP-OES/MS檢測(cè)聯(lián)用技術(shù)用于元素形態(tài)分析及金屬組學(xué)[75]研究的報(bào)道如同雨后春筍般不斷涌現(xiàn)，而其中將ETV-ICP-OES/MS作為后續(xù)檢測(cè)手段的研究工作相對(duì)甚少.Chery等[26]應(yīng)用聚丙烯酰胺凝膠電泳(PAGE)分離含硒蛋白，然后從PAGE板上截取出不同分子量的斑點(diǎn)物，將其引入ETV-ICP-MS進(jìn)行檢測(cè)，實(shí)現(xiàn)了實(shí)際樣品中硒蛋白的形態(tài)分析.Chen等[76]應(yīng)用毛細(xì)管電泳分離人血清中的鋁形態(tài)，然后利用FETV-ICP-OES離線檢測(cè)進(jìn)行鋁的組形態(tài)分析.

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