土壤重金屬快速檢測技術(shù)研究進展

毛雪飛，劉霽欣，錢永忠

土壤重金屬快速檢測技術(shù)研究進展

毛雪飛，劉霽欣，錢永忠

（中國農(nóng)業(yè)科學(xué)院農(nóng)業(yè)質(zhì)量標(biāo)準(zhǔn)與檢測技術(shù)研究所/農(nóng)業(yè)農(nóng)村部農(nóng)產(chǎn)品質(zhì)量安全重點實驗室，北京 100081）

近年來，隨著我國工農(nóng)業(yè)的高速發(fā)展，尤其是無節(jié)制的礦藏開采、“三廢”排放、汽車尾氣以及農(nóng)業(yè)化學(xué)投入品的濫用，重金屬污染已成為我國當(dāng)前最嚴(yán)重的環(huán)境污染問題之一，因此土壤重金屬監(jiān)測工作顯得尤為重要。但是，目前的土壤重金屬檢測標(biāo)準(zhǔn)方法仍以實驗室確證性分析為主，無法用于土壤重金屬的現(xiàn)場、快速分析，從而難以從源頭上及時、有效地對土壤重金屬污染進行監(jiān)測和預(yù)防，開發(fā)重金屬快速檢測設(shè)備和技術(shù)勢在必行。從土壤樣品的基質(zhì)特點來看，固體進樣分析是最可行的技術(shù)方案，主要包括電熱蒸發(fā)（ETV）原子光譜、X射線熒光光譜（XRF）、激光燒蝕（LA）、激光誘導(dǎo)擊穿光譜（LIBS）、X射線吸收光譜（XAS）、中子活化（INAA）等。上述固體進樣分析技術(shù)均無需樣品消解處理，高效、快捷，但是部分技術(shù)的檢出能力和穩(wěn)定性尚難以滿足土壤質(zhì)量標(biāo)準(zhǔn)的全部要求，如XRF、LA、LIBS，還有部分技術(shù)難以實現(xiàn)現(xiàn)場化，如LA、XAS、INAA等。因此，基于電熱蒸發(fā)（ETV）固體進樣的原子光譜分析技術(shù)在分析靈敏度、穩(wěn)定性和小型化方面具有特殊的優(yōu)勢。ETV是利用電加熱將樣品中的待測元素以氣溶膠的形式導(dǎo)入原子化器或激發(fā)源的技術(shù)，可實現(xiàn)土壤中常見重金屬元素的快速、高效導(dǎo)入，技術(shù)簡單、通用性強，適用于原子吸收、原子熒光、原子發(fā)射、無機質(zhì)譜等多種檢測系統(tǒng)。ETV常采用碳、金屬、石英等材料，如石墨管、多孔碳管、鎢絲、錸絲、石英管，其中利用高熔點金屬的電磁感應(yīng)電熱蒸發(fā)技術(shù)具有無冷點、升/降溫速度快、易于小型化的優(yōu)勢。但是，土壤樣品基質(zhì)復(fù)雜，基體干擾一直是困擾ETV技術(shù)應(yīng)用的核心瓶頸問題。新型的氣相富集（GPE）、介質(zhì)阻擋放電（DBD）、基體改進及背景校正等技術(shù)，有望實現(xiàn)土壤基體干擾的有效消除。特別是GPE技術(shù)，在特異性捕獲消除基體干擾的同時，還可以通過預(yù)富集提高儀器的分析靈敏度。通過上述技術(shù)的集成與創(chuàng)新，可以有效解決固體進樣的分析靈敏度和基體干擾問題，這將為土壤重金屬速測技術(shù)的研發(fā)提供新的思路，從而為土壤環(huán)境監(jiān)測與治理工作提供有效的技術(shù)支撐。

土壤；重金屬；快速檢測；電熱蒸發(fā)；固體進樣；基體干擾

0 引言

近年來，隨著我國工農(nóng)業(yè)的高速發(fā)展，尤其是無節(jié)制的礦藏開采、“三廢”排放、汽車尾氣以及農(nóng)業(yè)化學(xué)投入品的濫用，重金屬污染已成為我國當(dāng)前最嚴(yán)重的環(huán)境污染問題之一。2014年4月，環(huán)境保護部與國土資源部聯(lián)合發(fā)布的《全國土壤污染狀況調(diào)查公報》顯示：全國耕地土壤點位污染超標(biāo)率達19.4%，主要污染物為Cd、Ni、Cu、As、Hg、Pb等重金屬，會直接或間接影響到食品安全和人體健康。為了及時掌握、預(yù)警土壤中重金屬的污染情況，2016年國務(wù)院啟動了《土壤污染防治行動計劃》（土十條），提出了土壤環(huán)境質(zhì)量監(jiān)測點位對所有縣（市、區(qū)）全覆蓋的要求，在“土壤詳查”等工作中每年花費大量人力、物力和財力開展重金屬污染監(jiān)測。目前，土壤重金屬檢測的標(biāo)準(zhǔn)方法仍以實驗室確證性分析為主，如原子吸收光譜法（atomic absorption spectrometry，AAS）[1]、原子熒光光譜法（atomic fluorescence spectrometry，AFS）[2]、電感耦合等離子體發(fā)射光譜法（induced coupled plasma optical emission spectrometry，ICP-OES）[3]、電感耦合等離子體質(zhì)譜法（induced coupled plasma mass spectrometry，ICP-MS）[4]、波長色散型X射線熒光光譜法（wavelength dispersion X-ray fluorescence，WDXRF）[5]等。但是，上述方法需要復(fù)雜、耗時的樣品制備以及消解或提取處理，或較大的儀器尺寸和復(fù)雜精密的硬件配置，無法用于土壤的現(xiàn)場、快速分析，從而難以從源頭上及時、有效地對土壤重金屬污染進行監(jiān)測和預(yù)防。因此，本文對當(dāng)前重金屬快速檢測儀器與方法，及其對土壤樣品來說最核心的技術(shù)瓶頸——“基體干擾”問題進行綜述，以期為土壤環(huán)境監(jiān)測與治理研究提供技術(shù)參考。

1 土壤重金屬的固體進樣分析技術(shù)概述

與現(xiàn)有的液體進樣原子光譜方法相比，固體進樣分析是最有可能實現(xiàn)土壤重金屬現(xiàn)場快速檢測的技術(shù)，其無需消解處理，具有較高的樣品導(dǎo)入效率，可有效提高分析靈敏度、縮短分析時間、避免痕量元素的損失，同時減少有害化學(xué)試劑的使用，更加環(huán)保和安全。實際上，早期的原子光譜儀器大多基于固體樣品的直接分析，如鉀鹽、鈉鹽火焰發(fā)射譜線的觀測。現(xiàn)代意義上的固體進樣原子光譜儀器，可以追溯到1957年L’VOV[6]利用石墨坩堝電熱蒸發(fā)固體NaCl，采用AAS測定。這是現(xiàn)代石墨爐AAS（graphite furnace atomic absorption spectrometry，GF-AAS）的雛形，后經(jīng)Massmann改進為管式石墨爐，并由L’VOV設(shè)計增加了原子化平臺以改善空間溫度分布。

目前，可實現(xiàn)固體進樣元素分析的技術(shù)，主要包括電熱蒸發(fā)（electrothermal vaporization，ETV）[7]、XRF[8]、激光燒蝕（laser ablation，LA）[9]、激光誘導(dǎo)擊穿光譜（laser induced breakthrough spectrometry，LIBS）[10]、X射線光電子能譜（X-ray photoelectron spectroscopy，XPS）[11]、X射線吸收光譜（X-ray absorption spectroscopy，XAS）[12]、中子活化（instrumental neutron activation analysis，INAA）[13]等。其中，電熱蒸發(fā)（electrothermal vaporization，ETV）所需的材質(zhì)來源廣，易改裝和小型化，通用性強，是研究和應(yīng)用最多的固體進樣分析技術(shù)之一，將在下文予以專門闡述。

1.1 X射線熒光光譜法

XRF是指原子在X射線或粒子的激發(fā)下發(fā)射X射線熒光（0.01—10 nm），檢測器測量熒光的波長和強度從而實現(xiàn)元素的定性和定量分析。除了XRF，X射線光譜還有X射線衍射（X-ray diffraction，XRD）、XPS等。XRF是一種性能優(yōu)異的多元素分析手段，分析速度快，其中能量色散型XRF（energy dispersive X-ray fluorescence spectrometry，EDXRF）結(jié)構(gòu)簡單、功率較小，易于小型化，可用于現(xiàn)場快速檢測，已在地礦、鋼鐵、材料等領(lǐng)域獲得廣泛應(yīng)用[5, 8, 14-16]。但是，EDXRF的能量分辨率較差，對背景干擾較為敏感，常采用基體匹配作為標(biāo)準(zhǔn)曲線策略，同時對光源、濾光片、靶材、算法等加以優(yōu)化和改進，以提高分析靈敏度和消除基體干擾[14,16]。當(dāng)前的便攜式XRF對于土壤中Cu、Zn、As、Pb、Ni、Cr等元素的檢出能力可以達到土壤質(zhì)量標(biāo)準(zhǔn)的要求，仍難以滿足土壤中亞mg·kg-1級Cd和Hg元素的精準(zhǔn)測定需求。

1.2 激光樣品導(dǎo)入技術(shù)

LA[17]和LIBS[18]是利用高功率脈沖激光聚焦到固體樣品表面，使樣品等離子化或蒸發(fā)后以氣溶膠形式傳輸進入檢測器，簡單、快速，空間分辨率高，可用于元素的微區(qū)分析。其中，LA須與ICP-MS聯(lián)用，無法現(xiàn)場使用；LIBS構(gòu)造簡單，易于小型化、現(xiàn)場化。但是，由于激光激發(fā)樣品的絕對量過小，其分析靈敏度多在mg·kg-1以上級，同時受限于樣品表面特性對激光的吸收和激發(fā)效能差異，分析穩(wěn)定性仍是限制LA和LIBS進一步發(fā)展應(yīng)用的主要因素。目前，LA和LIBS主要用于常/微量元素的定性或半定量分析，還很難用于痕量重金屬的快速檢測。

1.3 等離子體進樣技術(shù)

分析儀器中常用的等離子體包括ICP、微波等離子體（MWP）等“高溫”等離子體，以及介質(zhì)阻擋放電（dielectric barrier discharge，DBD）、輝光放電、尖端放電等低溫等離子體（LTP），其蘊含豐富的能量可以激發(fā)或刻蝕固體樣品[19-22]。如DUAN等[19]研發(fā)了一種MWP-AES的直接固體進樣裝置，通過等離子體與固體樣品直接作用，將樣品加熱、使其元素原子化并連續(xù)激發(fā)，成功地測定了地質(zhì)樣品中Cu、Pb、Cr和Co等元素的含量。內(nèi)炬蒸發(fā)（ITV）技術(shù)是利用ICP的“高溫”等離子體作用將樣品中的元素蒸發(fā)和激發(fā)，再導(dǎo)入發(fā)射光譜或質(zhì)譜檢測器，實現(xiàn)了樣品激發(fā)與導(dǎo)入的“無縫”銜接，極大地提高了傳輸效率[23]。目前，ITV-ICP技術(shù)已用于部分生物和水樣品中Cr、V、Sr、Pb、Cd、Mn、Mg、Ca、Be、Zn、Ti、Ba等元素的分析[24-25]。但是，上述基于“高溫”等離子體技術(shù)的固體進樣儀器裝置依然存在功耗高、體積大的問題，難以用于現(xiàn)場快速分析。

此外，LTP也具有導(dǎo)入固體樣品中元素的能力，如XING等[20]將DBD-LTP探針與ICP-MS聯(lián)用，剝蝕薄層材料中的待測元素并轉(zhuǎn)化成氣溶膠，再導(dǎo)入檢測器；XING等[21]還利用該技術(shù)對巖石樣品中元素進行二維成像。相對于LA和LIBS，DBD-LTP探針結(jié)構(gòu)簡單、成本低廉，也是一種可行的微區(qū)分析技術(shù)[22]。但是，DBD-LTP的激發(fā)能力還不夠強，刻蝕的均勻性和分析的穩(wěn)定性還需進一步提高。

1.4 其他固體進樣技術(shù)

此外，XAS、INAA等儀器[12-13]可多元素分析，靈敏度高，其中XAS還可給出元素形態(tài)的特征信息。但是，XAS作為同步輻射大科學(xué)裝置，而INAA是一種放射性分析技術(shù)，兩者都無法用于土壤樣品的現(xiàn)場快速檢測。

2 電熱蒸發(fā)固體進樣技術(shù)

ETV是利用電加熱將樣品中的待測元素以干燥氣溶膠的形式導(dǎo)入原子化器或激發(fā)源的技術(shù)，有時ETV自身也是原子化器或激發(fā)源。ETV技術(shù)簡單，常采用碳、金屬、石英等材料；樣品導(dǎo)入快、進樣效率高，土壤中常見的重金屬元素都可以通過ETV實現(xiàn)導(dǎo)入[26-30]；同時，適用于原子吸收、原子熒光、原子發(fā)射、無機質(zhì)譜（ICP-MS）等多種檢測系統(tǒng)，通用性非常強。

2.1 碳材料ETV技術(shù)

碳材料ETV裝置最早源于L’VOV石墨坩堝原子化器，多制成管、舟、杯狀等作為進樣器[31-34]。其中，石墨爐原子吸收（graphite furnace atomic absorption spectrometry，GF-AAS）的石墨管是最常用的ETV裝置，在ETV-AAS上使用時既是蒸發(fā)器也是原子化器，但與ICP-MS/OES聯(lián)用時僅作為蒸發(fā)器，完成樣品的干燥、灰化和蒸發(fā)過程[35]。還有研究將W[36]、Ir[37]、Ta[33]等高熔點金屬熱解或電鍍在進樣器和石墨管表面，可有效改善管內(nèi)溫度分布、提高碳材料壽命。目前，基于碳材料的ETV技術(shù)已成功用于土壤、地礦、食品等樣品[34, 28-40]中Cd、Cu、Zn、Hg、Ni、Mn、Pb、As、Cr等數(shù)十種元素的分析。

但是，常用的石墨管ETV耗電高、散熱慢，需要復(fù)雜的冷卻和電源系統(tǒng)，難以小型化，如德國Jena公司生產(chǎn)的基于高聚焦短弧氙燈光源、中階梯光柵高分辨率分光系統(tǒng)和電荷耦合器件圖像傳感器（charge coupled device，CCD）檢測器的GF-AAS[41]。由于石墨爐的樣品承載量有限，必須將土壤樣品處理成干燥、均質(zhì)的粉末才能置入GF進行蒸發(fā)，一般在毫克級，這大大增加了樣品制備和分析過程的難度。LIU等[42]對多孔碳材料進行了改良，穩(wěn)定性與石墨管接近，但蒸發(fā)功耗僅需0.3—0.5 kW，遠低于后者，加上多孔碳自身的空隙大，因此散熱快，無需額外冷卻系統(tǒng)，對土壤中Cd的方法檢出限（limit of detection，LOD）可以達到μg·kg-1以下。同時，多孔碳樣品舟的樣品承載量可以達到100 mg，這些都為碳材料ETV裝置小型化及應(yīng)用提供了思路。

2.2 金屬材料ETV技術(shù)

高熔點金屬也是良好的ETV材料，如W、Mo、Pt、Ta、Re等，可制成絲、舟、管、片等形狀[37, 43]。金屬鎢具有良好的導(dǎo)電導(dǎo)熱性能和延展性，熔點高、化學(xué)惰性，并且成本低、易獲取，是當(dāng)前常用的ETV金屬材料。其中鎢絲（tungsten coil，TC）應(yīng)用最為廣泛，可與AAS、AFS、AES和ICP等串聯(lián)[44-45]，易于儀器小型化和便攜化，且不像GF那樣易與樣品成分產(chǎn)生難蒸發(fā)的碳化物，從而影響測定重現(xiàn)性。如HOU等[44]首次將TC-ETV直接插入Ar-H2火焰石英管原子化器中，形成了一種新型、小型化、緊湊的AFS進樣裝置，對Cd，Pb，Au和Ag等元素的絕對LOD分別可以達到0.02、0.6、2.5、4.4 pg；HOU等[45]比較了TC與不同的檢測器串聯(lián)的檢測技術(shù)，其中，TC-ETV-AAS中Cd的LOD為10 pg，而TC-ETV-AFS中As、Se、Cr、Sb和Pb的LOD分別為950、320、1400、330和160 fg（TC-ETV-AAS、TC-ETV-AFS的檢出能力在pg級，甚至更低）；當(dāng)與ICP串聯(lián)，其LOD與傳統(tǒng)ICP檢測器接近。為了防止金屬材料的氧化，使用TC時常在氬氣中補充氫氣作為還原性保護氣氛，并有提供自由基源、促進原子化的作用。

TC-ETV用于土壤樣品導(dǎo)入的主要難點在于樣品承載和基體干擾。由于TC無支撐結(jié)構(gòu)，無法承載固體樣品，因此一般多將土壤樣品制成懸浮液再導(dǎo)入TC，依靠表面張力承載，但最大也僅能加載10—20 μL。若將高熔點金屬制成舟或杯狀，雖然可以承載固體樣品[46-47]，如OKAMOTO等[46]利用鎢舟承載樣品并電熱蒸發(fā)，ICP-MS做為檢測器測定固體生物樣品中Cd的LOD為0.84 ng·g-1。但是對于直接電阻加熱方式，加熱體質(zhì)量或尺寸過大會導(dǎo)致過高的功率需求，以及升溫、導(dǎo)熱等性能的限制，這就失去了TC那樣的特殊優(yōu)勢。而且，部分研究中仍選擇將樣品消解后再加熱蒸發(fā)消解液進行元素測定[47]，依然難以實現(xiàn)現(xiàn)場快速檢測。

實際上，不管是碳材料還是高熔點金屬材料ETV，一般多采用電阻式加熱，必須在加熱體兩端引入電極，所以電極的接觸好壞對加熱的影響極大，而且易于損壞；另一方面，為保證電極的良好接觸，往往會在電極附近形成一個低溫區(qū)域，這個區(qū)域也容易造成元素的殘留，影響測定的穩(wěn)定性。本課題組研制的電磁感應(yīng)電熱蒸發(fā)器（inductive electrothermal vaporization，IETV），通過強制電流趨膚增加表面電阻，突破了常規(guī)鐵磁性金屬材料居里點1 200℃以上失磁無法繼續(xù)加熱的瓶頸，實現(xiàn)了非接觸ETV進樣。初步實驗結(jié)果表明，IETV裝置升溫速率＞300 ℃·s-1、最高溫度＞2 000 ℃，實現(xiàn)了樣品中Cd、Hg、As、Pb等元素的全部導(dǎo)入。

2.3 石英材料ETV技術(shù)

石英管（quartz tube，QT）是原子光譜中常用的原子化器，也可用于ETV，但受自身材料局限，耐受溫度最高僅有1 000 ℃左右，因此主要適用于Hg、Cd、Pb等中低溫元素。如基于催化熱解原理的測汞儀，一般采用QT-ETV來實現(xiàn)樣品中Hg的快速導(dǎo)入[48-50]，可用AAS或AFS檢測，是目前最為成功的基于ETV技術(shù)的商品化儀器，如有研究分別利用ETV-AFS與ETV-AAS檢測土壤中的Hg，其LOD分別為0.08、0.5 μg·kg-1[48-49]。針對測Hg時的基體干擾，主要采用金汞齊或塞曼扣背景的技術(shù)予以消除。此外，LIU和MAO等[7]研制了一體化石英管，前段QT-ETV作為進樣系統(tǒng)，后段QT作為氣相富集（gas phase enrichment，GPE）裝置用于預(yù)富集Pb，實現(xiàn)了食品樣品中Pb的直接固體進樣分析，方法LOD達到2—3 pg[7,51]。

3 基體干擾及消除技術(shù)

土壤樣品基質(zhì)成分復(fù)雜，除了大量的礦物質(zhì)，還富含微生物、腐殖質(zhì)等有機組分，直接電熱蒸發(fā)會導(dǎo)入大量的基體，如土壤樣品中共存元素的化學(xué)干擾、復(fù)雜基質(zhì)的背景干擾、微顆粒物的物理干擾、分子吸收干擾、特定元素的電離干擾等，可能對儀器的各個系統(tǒng)帶來不利影響，因此基體干擾一直是限制ETV技術(shù)廣泛應(yīng)用的瓶頸。為了實現(xiàn)固體進樣元素分析的準(zhǔn)確測定，研究者嘗試多種技術(shù)手段來消除基體干擾，如GPE[52-54]、基體改進劑[43,55-57]、標(biāo)準(zhǔn)加入法[30]、基體匹配[58]、塞曼背景校正[59]、程序升溫[7, 52-54,60]以及化學(xué)計量學(xué)校正[61]等。

3.1 氣相富集技術(shù)

GPE主要以氣相分析物為對象，如ETV[51-54]、化學(xué)蒸氣發(fā)生（chemical vapor generation，CVG）[62-63]都是較好的氣相導(dǎo)入技術(shù)，所以GPE裝置大多直接耦合到原子光譜儀器中，效率高、通用性強。早期的原子光譜儀器由于分析靈敏度不高，為了提高元素檢出能力，常采用氣球法[64]、冷凝法[65]、溶液/固體吸附[66-68]等方法對氣相分析物進行預(yù)富集。這是GPE技術(shù)最初的用途，當(dāng)時的GPE裝置結(jié)構(gòu)復(fù)雜、操作繁瑣。近年來，隨著材料、等離子體等技術(shù)的發(fā)展，與GPE密切相關(guān)的材料表面改性、快速升降溫、微等離子體放電均可簡單實現(xiàn)，這為GPE的發(fā)展提供了新的思路。

GPE在儀器系統(tǒng)中的主要作用有兩點：一是通過預(yù)富集提高分析靈敏度；二是通過與基體干擾物的分離作用降低或消除基體干擾。常見的GPE捕獲材料主要有石英、碳、金屬材料等，如石英管[62-63,69-71]、石墨爐[72-75]、金絲[53,76-77]、鎢絲[42,52-54,78-80]、鍍貴金屬的鎢絲[81-82]等；捕獲/釋放方式主要有冷/熱處理[65,83]、合金捕獲[53,60]、放電捕獲/釋放[62-63,71]等。對于GPE的樣品導(dǎo)入，HG[62-63]是研究最多的方式，但只適用于液相分析物，或部分元素的固體懸浮液/泥漿法[84]進樣分析。若將GPE技術(shù)用于土壤樣品ETV導(dǎo)入時的基體干擾消除，則可充分發(fā)揮兩種技術(shù)的優(yōu)勢，有望實現(xiàn)土壤重金屬的直接進樣分析。

3.1.1 ETV與GPE聯(lián)用 目前，GPE與ETV聯(lián)用的研究還相對較少，只有Hg、Cd、Pb、As等元素可以分別通過金阱（捕Hg）[53]、鎢阱（捕Cd）[42,85]和石英阱（捕Pb、As）[7,86]實現(xiàn)氣相富集，其中最成功的測汞儀和測鎘儀已實現(xiàn)商品化，儀器檢出限可達pg—ng級別，可用于土壤的固體進樣快速檢測。但是，目前尚無研究將金、鎢、石英等捕獲材料有效耦合，實現(xiàn)多種目標(biāo)重金屬元素的同時捕獲，這也是ETV-GPE技術(shù)的難點之一。對于土壤的基體干擾，由于Hg的蒸發(fā)溫度較低，不易蒸出大量干擾基體，因此催化熱解-金汞齊原理的測汞儀可以完全消除測Hg時的干擾，實現(xiàn)溶液標(biāo)準(zhǔn)曲線的直接定值。但是，蒸發(fā)溫度越高，隨蒸發(fā)攜帶的基體干擾則更為復(fù)雜，由于尚未摸清具體干擾的來源和作用機制，目前還很難完全消除土壤中Cd、Pb、As等元素的基體干擾，仍需使用標(biāo)準(zhǔn)加入法或基體匹配法予以校正。

3.1.2 介質(zhì)阻擋放電GPE技術(shù) DBD亦稱無聲放電，是一種常溫常壓下非平衡態(tài)交流放電技術(shù)，也是一種產(chǎn)生低溫等離子的有效方式，常用作原子光譜的原子化器、發(fā)射光譜激發(fā)源和化學(xué)蒸氣發(fā)生源[87-89]。KRATZER等[90]最早報道了DBD作為原子化器時Bi的殘留問題，但未能實現(xiàn)捕獲和釋放過程的精確控制。LIU等[62-63]利用同軸型雙介質(zhì)層DBD裝置，構(gòu)建了氫化物發(fā)生（hydride generation，HG）DBD-AFS系統(tǒng)，實現(xiàn)了O2和H2氣氛切換下DBD 對As捕獲/釋放的精確控制，As的LOD可以達到1.0 ng·L-1，分析靈敏度提高一個數(shù)量級。與石英、石墨爐、金屬等GPE技術(shù)相比，DBD能夠?qū)崿F(xiàn)常溫下對待測元素的捕獲和釋放，無需加熱過程，釋放快，并可避免因溫度反復(fù)變化而出現(xiàn)的捕獲材料退化問題。

此外，由于DBD中包含紫外輻射以及大量自由基、離子、激發(fā)態(tài)原子、分子碎片等化學(xué)性質(zhì)異?；钴S物質(zhì)，對有機物具有非常好的降解效果[89,91-93]，具有消除ETV導(dǎo)入的有機干擾物的能力。本課題組已經(jīng)研發(fā)了相關(guān)的干擾消除裝置，并申請了國家發(fā)明專利。總體來看，DBD裝置價格低廉、結(jié)構(gòu)簡單、尺寸小巧，通用性強，HG和ETV[89]均可實現(xiàn)樣品導(dǎo)入，是一種簡單、低耗、易控的捕獲/釋放元素手段和有機干擾消除技術(shù)，有潛力在ETV-GPE中得到廣泛應(yīng)用。

3.2 基體改進劑技術(shù)

又稱化學(xué)改進劑，是改善基體干擾最常用的方法，如鈀等鉑系金屬固體顆粒[44]或鹽[94]、磷酸鹽[55]、銨鹽[95]、鎂鹽[96]、Triton X-100[97]、四甲基氫氧化銨[98]、NaF[99]、PTFE[100]、8-羥基喹啉[101]以及混合改進劑[102]等，通過與干擾元素或待測元素結(jié)合以降低或提高蒸發(fā)溫度而與基體分離，還有改善原子化環(huán)境、助熔、避免難熔物產(chǎn)生等作用。目前，上述基體改進劑在液體進樣系統(tǒng)的GF-AAS上使用最多。然而，由于改進劑需要與樣品中待測元素或干擾物質(zhì)充分反應(yīng)才能發(fā)揮作用，因此與固體的土壤粉末樣品很難充分接觸。有研究[103]采用懸浮液技術(shù)制備土壤樣品，再與基體改進劑混合使用，但是土壤的懸浮液制備難度較大，同時干擾消除效果也非常有限。其實，原先在催化劑合成領(lǐng)域廣泛使用的“自發(fā)單層分散”（spontaneous monolayer dispersion，SMD）理論[104]，恰好具備在ETV過程中實現(xiàn)的可能，也就是說樣品中的待測元素可以通過“載體”表面的自發(fā)分散，而與基體干擾物分離，從而有可能消除ETV的化學(xué)干擾。

此外，最早由SHUTTLER提出的持久性化學(xué)改進劑也是常用的基體改進技術(shù)[105]，主要使用高熔點金屬Ir、Pd、Pt、Rh、Ru等，生成難熔化合物的Hf、Mo、Nb、Re、Ta、Ti、V、W、Zr等，以及生成共價碳化物的B、Si等[100]，或者上述改進劑的混合使用。持久性化學(xué)改進劑主要采用涂覆、鍍層等方式用于原子化器、電熱蒸發(fā)器，可反復(fù)使用，并延長加熱裝置壽命。但為了減少持久性化學(xué)改進劑的損失，必須嚴(yán)格控制加熱的溫度。由于直接ETV導(dǎo)入的固體土壤樣品基體過于復(fù)雜，在持久性化學(xué)改進劑的實際使用過程中，不僅基體干擾消除作用效果不明顯，而且會嚴(yán)重縮短其使用壽命。

3.3 標(biāo)準(zhǔn)加入與基體匹配法

基體匹配或標(biāo)準(zhǔn)加入法做標(biāo)線也是一種可行的基體干擾校正方法[106]，若有條件獲得基體標(biāo)物，其固體便攜的特點也較為適于現(xiàn)場操作，可以提前準(zhǔn)備好標(biāo)曲所需的基體樣品，在現(xiàn)場直接上機使用。如OLESZCZUK等[106]在研究中利用固體標(biāo)準(zhǔn)物質(zhì)校準(zhǔn)檢測咖啡樣品中的Cu，LOD為0.06 μg·g-1。但是，與基體相近或待測元素濃度已知的標(biāo)準(zhǔn)物質(zhì)不易獲得，需要提前篩選大量的典型樣品基體，構(gòu)建樣品庫進行基體分類與校正，并且現(xiàn)場需要預(yù)判樣品適用的基體類型，大大增加了分析難度。其實，基體匹配的方法只能校正與濃度無關(guān)的干擾，終究只是一種有限的補救措施。

3.4 其他基體干擾消除技術(shù)

其他一些技術(shù)也可以實現(xiàn)部分元素或特定條件下的基體干擾消除，如塞曼背景校正、程序升溫、連續(xù)光源與高分辨率分光系統(tǒng)的背景校正等。德國Jena公司在固體進樣GF-AAS中將高聚焦短弧氙燈光源、中階梯光柵高分辨率分光系統(tǒng)和CCD檢測器技術(shù)聯(lián)用發(fā)揮到了極致，通過背景校正技術(shù)實現(xiàn)了毫克級樣品的直接進樣與基體干擾消除[107-108]，但對于復(fù)雜基質(zhì)的土壤樣品仍顯得捉襟見肘。另外，塞曼扣背景是AAS常用的背景校正技術(shù)，在ETV進樣方面應(yīng)用最為成功的是Lumex公司生產(chǎn)的基于塞曼背景校正AAS技術(shù)的測汞儀，對于基體較為簡單的土壤樣品或者進樣量較少的情況下，可以實現(xiàn)溶液標(biāo)準(zhǔn)曲線直接定值。LIU等[53]利用Hg和Cd元素的蒸發(fā)溫度差，實現(xiàn)了樣品中兩種元素的順序蒸發(fā)，并利用金阱、鎢阱分別捕獲Hg和Cd，LOD分別為0.07、0.05 μg·kg-1，這也是利用程序升溫技術(shù)消除基體干擾的一種嘗試。

4 土壤重金屬快速檢測技術(shù)發(fā)展的思考

當(dāng)前，土壤重金屬的現(xiàn)場快速檢測已經(jīng)列入國家重大科研需求。要實現(xiàn)土壤重金屬現(xiàn)場、快速、準(zhǔn)確測定的目標(biāo)，無論是樣品消解還是提取處理都無法滿足實際的檢測需求，因此無需消解處理的固體進樣元素分析技術(shù)已成為最可行的技術(shù)方案。在諸多的固體進樣元素分析技術(shù)中，XRF、LIBS和ETV均具有自身的優(yōu)劣勢，其中XRF有可能解決土壤重金屬mg·kg-1級或亞mg·kg-1級的檢測需求，也是當(dāng)前重金屬快速檢測儀器市場表現(xiàn)較為突出的技術(shù)。但是，若要進一步提升固體進樣技術(shù)的分析靈敏度，特別是XRF難以解決的Hg和Cd等痕量重金屬的檢測問題，ETV技術(shù)則具有特殊的優(yōu)勢。ETV作為一種簡單、高效、通用性強的進樣方式，在樣品導(dǎo)入過程中幾乎不會損失，因此具有較高的樣品導(dǎo)入效率；同時，適用于吸收、熒光、發(fā)射等多種原子光譜檢測器以及無機質(zhì)譜，可以達到pg級的絕對檢出能力，因此是一種極具潛力的固體樣品導(dǎo)入技術(shù)。但是，由于固體樣品復(fù)雜基質(zhì)的直接導(dǎo)入，不可避免地帶來不同程度的基體干擾，從而影響測試的靈敏度、準(zhǔn)確度和精密度。特別對ETV技術(shù)，其蒸發(fā)出來的大量基體氣溶膠可能對儀器的各個系統(tǒng)帶來不利影響，因此基體干擾一直是限制其廣泛應(yīng)用的瓶頸。總體來說，當(dāng)前急需系統(tǒng)性地研究ETV過程中土壤基體干擾的來源及作用機制，以期為消除干擾提出理論支撐。同時，通過GPE、DBD[109]、基體改進、背景校正等技術(shù)的創(chuàng)新與集成，有望實現(xiàn)土壤基體干擾的有效消除，構(gòu)建電熱固體進樣的重金屬速測儀器設(shè)備。這也是固體進樣元素分析技術(shù)體系中非常重要的一個環(huán)節(jié)，從而最終為實現(xiàn)土壤重金屬的現(xiàn)場、快速、準(zhǔn)確測定提供可靠的技術(shù)手段。

[1] FRIMPONG S, KORANTENG S. Levels and human health risk assessment of heavy metals in surface soil of public parks in Southern Ghana., 2019, 191(9): 588-602.

[2] GENG W H, NAKAJIMA T, TAKANASHI H, OHKI A. Determination of mercury in ash and soil samples by oxygen flask combustion method--cold vapor atomic fluorescence spectrometry (CVAFS)., 2008, 154(1/3): 325-330.

[3] TIGHE M, LOCKWOOD P, WILSON S, LISLE L. Comparison of digestion methods for ICP-OES analysis of a wide range of analytes in heavy metal contaminated soil samples with specific reference to arsenic and antimony., 2006, 35(9/10): 1369-1385.

[4] ODUKOYA A, OLOBANIYI S, OLUSEYI T. Assessment of Potentially Toxic Elements Pollution and Human Health Risk in Soil of Ilesha Gold Mining Site, Southwest Nigeria., 2018, 91(6): 743-748.

[5] SHIBATA Y, SUYAMA J, KITANO M, NAKAMURA T. X-ray fluorescence analysis of Cr, As, Se, Cd, Hg, and Pb in soil using pressed powder pellet and loose powder methods., 2009, 38(5): 410-416.

[6] L’VOV B. Fifty Years of Atomic Absorption Spectrometry.ry, 2005, 60(4): 382-392.

[7] FENG L, LIU J X, MAO X F, LU D, ZHU X F, QIAN Y Z. An integrated quartz tube atom trap coupled with solid sampling electrothermal vapourization and its application to detect trace lead in food samples by atomic fluorescence spectrometry., 2016, 31(11): 2253-2260.

[8] ALMEIDA E, DURAN N M, GOMES M H F, SAVASSA S M, DA CRUZ T N M, MIGLIAVACCA R A, DE CARVALHO H W P. EDXRF for elemental determination of nanoarticle‐related agricultural samples., 2019, 48(2): 151-161.

[9] ABREGO Z, UNCETA N, SANCHEZ A, CABALLERO A G, OCHOA L M B, GOICOLEA M A, BARRIO R. Determination of mercury(ii) in water at sub-nanomolar levels by laser ablation-ICPMS analysis of screen printed electrodes used as a portable voltammetric preconcentration system., 2017, 142(7): 1157-1164.

[10] LI J M, XU M L, MA Q X, ZHAO N, LI X Y, ZHANG Q M, GUO L, LU Y F. Sensitive determination of silicon contents in low-alloy steels using micro laser-induced breakdown spectroscopy assisted with laser-induced fluorescence., 2019, 194: 697-702.

[11] KUBALA A, BANA? D, STABRAWA I, SZARY K, SOBOTA D, MAJEWSKA U, WUDARCZYK-MOCKO J, BRAZIEWICZ J, PAJEK M. Analysis of Ti and TiO2nanolayers by total reflection X-ray photoelectron spectroscopy., 2018, 145: 43-50.

[12] STELLATO F, CALANDRA M, D'ACAPITO F, DE SANTIS E, LA PENNA G, ROSSI G, MORANTE S. Multi-scale theoretical approach to X-ray absorption spectra in disordered systems: an application to the study of Zn(ii) in water., 2018, 20(38): 24775-24782.

[13] REZA P, ALIASGHAR F, ELHAM M. Determination of trace elements in the seeds of fruits using instrumental neutron activation analysis (INAA) in Arak, I.R. Iran., 2017, 315(1): 89-93.

[14] VANHOOF C, BACON J, ELLIS A, VINCZE L, WOBRAUSCHEK P. Atomic spectrometry update - a review of advances in X-ray fluorescence spectrometry and its special applications., 2018, 33(9): 1413-1431.

[15] SERVIN A, CASTILLO-MICHEL H, HERNANDEZ-VIEZCAS J, DIAZ B, PERALTA-VIDEA J, GARDEA-TORRESDEY J. Synchrotron micro-XRF and micro-XANES confirmation of the uptake and translocation of TiO2nanoparticles in cucumber () plants., 2012, 46(14): 7637-7643.

[16] PEREZ R, FALCHINI G, VINCENTE F, SOARES L, POLETTI M, SANCHEZ H. A new XRF spectrometer using a crystal monochromator and parallel plates beam guides., 2019, 440: 48-53.

[17] KANTOR T. Electrothermal vaporization and laser ablation sample introduction for flame and plasma spectrometric analysis of solid and solution samples., 2001, 56(9): 1523-1563.

[18] SANTOS D, NUNES L, DE CARVALHO G, GOMES M, DE SOUZA P, LEME F, DOS SANTOS L, KRUG F. Laser-induced breakdown spectroscopy for analysis of plant materials: A review., 2012, 71-72: 3-13.

[19] NIU G, SHI Q, YUAN X, WANG J, WANG X, DUAN Y. Combination of support vector regression (SVR) and microwave plasma atomic emission spectrometry (MWP-AES) for quantitative elemental analysis in solid samples using the continuous direct solid sampling (CDSS) technique.2018, 33(11): 1954-1961.

[20] XING Z, WANG J A, HAN G J, KUERMAITI B, ZHANG S C, ZHANG X R. Depth profiling of nanometer coatings by low temperature plasma probe combined with inductively coupled plasma mass spectrometry.2010, 82(13): 5872-5877.

[21] XING Z, YANG M, GUO W, JIN L L, LIU Z F, HU S H. Elemental imaging method based on a dielectric barrier discharge probe coupled with inductively coupled plasma mass spectrometry., 2018, 147: 141-148.

[22] 李銘, 李健, 陳帥, 楊萌, 黃秀, 馮璐, 范博文, 邢志. 低溫等離子體探針-原子熒光光譜法檢測鎘元素的方法研究. 分析儀器, 2017, 2: 53-57.

LI M, LI J, CHEN S, YANG M, HUAMG X, FENG L, FAN B W, XING Z. Determination of cadmium by low temperature plasma probe-atomic fluorescence spectrometry., 2017, 2: 53-57. (in Chinese)

[23] KARANASSIOS V, DROUIN P, REYNOLDS G G. Electrically heated wire-loop，in-torch vaporization (ITV) sample introduction system for ICP-AES with photomultiplier tube detection and ICP-MS., 1995, 50: 4-7.

[24] BADIEI H R, LAI B, KARANASSIOS V. Micro- and nano-volume samples by electrothermal, near - torch vaporization sample introductionusing removable, interchangeable and portable rhenium coiled-filament assemblies and axially-viewed inductively coupled plasma -atomic emission spectrometry., 2012, 77: 19-30.

[25] BADIEI H R, LIU C, KARANASSIOS V. Taking part of the lab to the sample: On - site electrodeposition of Pb followed by measurement in a lab using electrothermal, near-torch vaporization sample introduction and inductively coupled plasma-atomic emission spectrometry., 2013, 108: 131-136.

[26] SARDANS J, MONTES F, PE?UELAS J. Electrothermal atomic absorption spectrometry to determine As, Cd, Cr, Cu, Hg, and Pb in soils and sediments: A review and perspectives., 2011, 20(4): 447-491.

[27] 黃亞濤, 毛雪飛, 劉霽欣, 王敏, 張立華, 馮禮, 湯曉艷, 周劍. 電熱蒸發(fā)鎢絲在線捕獲原子熒光光譜法直接測定菠菜中痕量鎘. 分析化學(xué), 2013, 41(10): 1587-1591.

HUANG Y T, MAO X F, LIU J X, WANG M, ZHZNG L H, FENG L, TANG X Y, ZHOU J. Direct determination of ultratrace cadmium in spinach by electrothermal vaporization atomic fluorescence spectrometry using on-line atom trap of tungsten coil., 2013, 41(10): 1587-1591. (in Chinese)

[28] COSTLEY C T, MOSSOP K F, DEAN J R, GARDEN L M, MARSHALL J, CARROLL J. Determination of mercury in environmental and biological samples using pyrolysis atomic absorption spectrometry with gold amalgamation., 2000, 405(1/2): 179-183.

[29] BELARRA M, RESANO M, VANHAECKE F, MOENS, L. Direct solid sampling with electrothermal vaporization/atomization: what for and how?2002, 21(12): 828-839.

[30] RESANO M, VANHAECKE F, DE LOOS-VOLLEBREGT M T C. Electrothermal vaporization for sample introduction in atomic absorption, atomic emission and plasma mass spectrometry-a critical review with focus on solid sampling and slurry analysis., 2008, 23(11): 1450-1475.

[31] REYES M N M, CAMPOS R C. Determination of copper and nickel in vegetable oils by direct sampling graphite furnace atomic absorption spectrometry., 2006, 70(5): 929-932.

[32] FRIESE K C, HUANG M D, SCHLEMMER G, KRIVAN V. A two-step atomizer system using a transversely heated furnace with Zeeman background correction: Design and first solid sampling applications., 2006, 61(9): 1054-1062.

[33] 張巖, 呂品, 李揮, 王多, 劉敬澤. 涂鉭石墨管-石墨爐原子吸收法測定食品中鋁含量. 食品科學(xué), 2008, 29(11): 498-500.

ZHANG Y, Lü P, LI H, WANG D, LIU J Z. Determination of aluminum in food with tantalum-coated graphite tube-graphite furnace atomic absorption spectrometry., 2008, 29(11): 498-500. (in Chinese)

[34] CHEN S Z, LU D B, XU Q Y. Electrothermal Vaporization in inductively coupled plasma atomic emission spectrometry for direct multielement analysis of food samples with slurry sampling., 2004, 49(5): 290-295.

[35] KAVEH F, BEAUCHEMIN D. Improvement of the capabilities of solid sampling ETV-ICP-OES by coupling ETV to a nebulisation/pre- evaporation system., 2014, 29(8): 1371-1377.

[36] REGO J F, VIRGILIO A, NOBREGA J A, NETO J A G. Determination of lead in medicinal plants by high-resolution continuum source graphite furnace atomic absorption spectrometry using direct solid sampling., 2012, 100: 21-26.

[37] VASSILEVA E, BAETEN H, HOENIG M. Advantages of the iridium permanent modifier in fast programs applied to trace-element analysis of plant samples by electrothermal atomic absorption spectrometry., 2001, 369(6): 491-495.

[38] MELLO P A, PEDROTTI M F, CRUZ S M, MULLER E I, DRESSLER V L, FLORES E M M. Determination of rare earth elements in graphite by solid sampling electrothermal vaporization- inductively coupled plasma mass spectrometry., 2015, 30(10): 2048-2055.

[39] WU C H, JIANG S J, SAHAYAM A C. Using electrothermal vaporization inductively coupled plasma mass spectrometry to determine S, As, Cd, Hg, and Pb in fuels., 2018, 147: 115-120.

[40] TINAS H, OZBEK N, AKMAN S. Determination of lead in flour samples directly by solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry., 2018, 140: 73-75.

[41] SOARES B M, SANTOS R F, BOLZAN R C, MULLER E I, PRIMEL E G, DUARTE F A. Simultaneous determination of iron and nickel in fluoropolymers by solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry., 2016, 160: 454-460.

[42] FENG L, LIU J X. Solid sampling graphite fibre felt electrothermal atomic fluorescence spectrometry with tungsten coil atomic trap for the determination of cadmium in food samples., 2010, 25(7): 1072-1078.

[43] BRUHN C G, HUERTA V N, NEIRA J Y. Chemical modifiers in arsenic determination in biological materials by tungsten coil electrothermal atomic absorption spectrometry.2004, 378(2): 447-455.

[44] JIANG X M, WU P, DENG D Y, GAO Y, HOU X D, ZHENG C B. A compact electrothermal-flame tandem atomizer for highly sensitive atomic fluorescence spectrometry., 2012, 27(10): 1780-1786.

[45] HOU X D, LEVINE K E, SALIDO A, JONES B T, EZER M, ELWOOD S, SIMEONSSON J B. Tungsten coil devices in atomic spectrometry: Absorption, fluorescence, and emission., 2001, 17(1): 175-180.

[46] OKAMOTO Y. Furnace-fusion system for the direct determination of cadmium in biological samples by inductively coupled plasma atomic emission spectrometry using tungsten boat furnace-sample cuvette technique., 1999, 14(11): 1767-1770.

[47] MATSUMOTO A, OSAKI S, KOBATA T, HASHIMOTO B, UCHIHARA H, NAKAHARA T. Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry., 2010, 95(1): 85-89.

[48] 李菊蘭, 林建奇. 電熱蒸發(fā)-直接進樣-原子熒光光譜法檢測土壤中的汞. 糧食科技與經(jīng)濟, 2017, 42(4): 49-51.

LI J L, LIN J Q. Determination of Mercury in soil by electrothermal evaporation-direct injection-atomic fluorescence spectrometry.2017, 42(4): 49-51. (in Chinese)

[49] 孫鵬, 劉海濤, 李崇江, 林建奇, 任晉源, 閆麗明, 李威, 趙慷. 電熱蒸發(fā)-直接進樣-冷原子吸收光譜法測定土壤以及沉積物中汞. 中國無機分析化學(xué), 2018, 8(1): 6-10.

SUN P, LIU H T, LI C J, LIN J Q, REN J Y, YAN L M, LI W, ZHAO K. Determination of mercury in soil and sediment by electrothermal evaporation-direct injection-cold atomic absorption spectrometry., 2018, 8(1): 6-10. (in Chinese)

[50] 林建奇, 孫鵬, 李崇江, 閆麗明, 任晉源, 李威, 林達芳. 鍍金石英砂富集-冷原子吸收光譜法測定環(huán)境空氣中的汞. 化學(xué)分析計量, 2018, 27(1): 55-58.

LIN J Q, SUN P, LI C J, YAN L M, REN J Y, LI W, LIN D F. Determination of mercury in ambient air by gold-plated quartz sand enrichment-cold atomic absorption spectrometry., 2018, 27(1): 55-58. (in Chinese)

[51] SHANG D R, ZHAO Y F, ZHAI Y X, NING J S, DUAN D L, ZHOU Y D. Direct determination of lead in foods by solid sampling electrothermal vaporization atomic fluorescence spectrometry., 2016, 32(9): 1007-1010.

[52] ZHANG Y, MAO X F, LIU J X, WANG M, QIAN Y Z, GAO C L, QI Y H. Direct determination of cadmium in foods by solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry using a tungsten coil trap., 2016, 118: 119-126.

[53] WANG B, FENG L, MAO X F, LIU J X, YU C C, DING L, LI S Q, ZHENG C M, QIAN Y Z. Direct determination of trace mercury and cadmium in food by sequential electrothermal vaporization atomic fluorescence spectrometry using tungsten and gold coil traps., 2018, 33(7): 1209-1216.

[54] ZHANG Y, MAO X F, WANG M, GAO C L, QI Y H, QIAN Y Z, TANG X Y, ZHOU J. Direct determination of cadmium in grain by solid sampling electrothermal vaporization atomic fluorescence spectrometry with a tungsten coil trap., 2015, 48(18): 2908-2920.

[55] 龔文杰, 馬建明, 趙立達. 微波消解-石墨爐原子吸收法測定小海鮮產(chǎn)品中的鉛和鎘. 中國衛(wèi)生檢驗雜志, 2011, 21(7): 1663-1665.

GONG W J, MA J M, ZHAO L D. Determination of lead and cadmium in small seafood products by microwave digestion-graphite furnace atomic absorption spectrometry., 2011, 21(7): 1663-1665. (in Chinese)

[56] LI Y C, JIANG S J. Determination of Cu, Zn, Cd and Pb in Fish samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry.1998, 359(1/2): 205-212.

[57] YI Y Z, JIANG S J, SAHAYAM A C. Palladium nanoparticles as the modifier for the d-termination of Zn, As, Cd, Sb, Hg and Pb in biological samples by ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry., 2012, 27(3): 426-431.

[58] CARRION N, ITRIAGO A M, ALVAREZ M A, ELJURI E. Simultaneous determination of lead, nickel, tin and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS., 2003, 61(5): 621-632.

[59] THONGSAW A, SANANMUANG R, UDNAN Y, ROSS G M, CHAIYASITH W C. Speciation of mercury in water and freshwater fish samples using two-step hollow fiber liquid phase microextraction with electrothermal atomic absorption spectrometry., 2019, 152: 102-108.

[60] MAO X F, ZHANG Y, LIU J X, WANG M, QIAN Y Z, ZHANG Z W, QI Y H, GAO C L. Simultaneous trapping of Zn and Cd by a tungsten coil and its application to grain analysis using electrothermal inductively coupled plasma mass spectrometry., 2016, 6(54): 48699-48707.

[61] MAO X F, LIU J X, HUANG Y T, FENG L, ZHANG L H, TANG X Y, ZHOU J, QIAN Y Z, WANG M. Assessment of homogeneity and minimum sample mass for cadmium analysis in powdered certified reference materials and real rice samples by solid sampling electrothermal vaporization atomic fluorescence spectrometry., 2013, 61(4): 848-853.

[62] MAO X F, QI Y H, HUANG J W, LIU J X, CHEN G Y, NA X, WANG M, QIAN Y Z. Ambient-temperature trap/release of arsenic by dielectric barrier discharge and its application to ultratrace arsenic determination in surface water followed by atomic fluorescence spectrometry., 2016, 88(7): 4147-4152.

[63] QI Y H, MAO X F, LIU J X, NA X, CHEN G Y, LIU M T, ZHENG C M, QIAN Y Z. In situ dielectric barrier discharge trap for ultrasensitive arsenic determination by atomic fluorescence spectrometry., 2018, 90(10): 6332-6338.

[64] 郭旭明, 郭小偉, 黃本立. 氫化物的氣相富集及其在超痕量分析中的應(yīng)用. 光譜學(xué)與光譜分析, 2000(4): 533-536.

GUO X M, GUO X W, HUANG B L. Gas phase enrichment of hydride and its application in ultra-trace analysis., 2000(4): 533-536. (in Chinese)

[65] CHEN G Y, LAI B, MAO X F, CHEN T W, CHEN M M. Continuous arsine detection using a peltier-effect cryogenic trap to selectively trap methylated arsines., 2017, 89(17): 8678-8682.

[66] YOGARAJAH N, TSAI S S H. Detection of trace arsenic in drinking water: challenges and opportunities for microfluidics., 2015, 1(4): 426-447.

[67] SHAMSIPUR M, FATTAHI N, ASSADI Y, SADEGHI M, SHARAFI K. Speciation of As(III) and As(V) in water samples by graphite furnace atomic absorption spectrometry after solid phase extraction combined with dispersive liquid-liquid microextraction based on the solidification of floating organic drop., 2014, 130: 26-32.

[68] HAGIWARA K, INUI T, KOIKE Y, AIZAWA M, NAKAMURA T. Speciation of inorganic arsenic in drinking water by wavelength- dispersive X-ray fluorescence spectrometry after in situ preconcentration with miniature solid-phase extraction disks., 2015, 134: 739-744.

[69] KILIN? E, BAKIRDERE S, AYDIN F, ATAMAN O Y. In situ atom trapping of Bi on W-coated slotted quartz tube flame atomic absorption spectrometry and interference studies., 2013, 89: 14-19.

[70] KILIN? E, BAKIRDERE S, AYDIN F, ATAMAN O Y. Sensitive determination of bismuth by flame atomic absorption spectrometry using atom trapping in a slotted quartz tube and revolatilization with organic solvent pulse., 2012, 73: 84-88.

[71] KRATZER J, MUSIL S, MARSCHNER K, SVOBODA M, MATOUSEK T, MESTER Z, STURGEON R E, DEDINA J. Behavior of selenium hydride in heated quartz tube and dielectric barrier discharge atomizers., 2018, 1028: 11-21.

[72] DO?EKAL B, DEDINA J, KRIVAN V. Radiotracer investigation of hydride trapping efficiency within a graphite furnace., 1997, 52(6): 787-794.

[73] SHALTOUT A A, CASTILHO I N B, WELZ B, CARASEK E, MARTENS I B G, MARTENS A, COZZOLINO S M F. Method development and optimization for the determination of selenium in bean and soil samples using hydride generation electrothermal atomic absorption spectrometry., 2011, 85(3): 1350-1356.

[74] FURDíKOVá Z, DO?EKAL B. Trapping interference effects of arsenic, antimony and bismuth hydrides in collection of selenium hydride within iridium-modified transversally-heated graphite tube atomizer., 2009, 64(4): 323-328.

[75] ?I?MA J, RYCHLOVSKY P. Electrochemical selenium hydride generation with in situ trapping in graphite tube atomizers., 2003, 58(5): 919-930.

[76] COSTLEY C T, MOSSOP K F, DEAN J R, GARDEN L M, MARSHALL J, CARROLL J. Determination of mercury in environmental and biological samples using pyrolysis atomic absorption spectrometry with gold amalgamation., 2000, 405(1/2): 179-183.

[77] RIVARO P, IANNI C, SOGGIA F, FRACHE R. Mercury speciation in environmental samples by cold vapour atomic absorption spectrometry with in situ preconcentration on a gold trap., 2007, 158(3/4): 345-352.

[78] TITRETIR S, KENDüZLER E, ARSLAN Y, KULA I, BAKIRDERE S, ATAMAN O Y. Determination of antimony by using tungsten trap atomic absorption spectrometry., 2008, 63(8): 875-879.

[79] CANKUR O, ATAMAN O Y. Chemical vapor generation of Cd and on-line preconcentration on a resistively heated W-coil prior to determination by atomic absorption spectrometry using an unheated quartz absorption cell., 2007, 22(7): 791-799.

[80] 王金玉, 黃亞濤, 毛雪飛, 王敏, 焦必寧, 張英. 鎢絲捕獲-電熱蒸發(fā)原子熒光光譜法直接測定飲料中痕量鎘. 食品科學(xué), 2013, 34(24): 131-134.

WANG J Y, HUANG Y T, MAO X F, WAMG M JIAO B N, ZHANG Y. Direct determination of ultra-trace amounts of cadmium in beverages by tungsten coil trapping electrothermal vaporization atomic fluorescence spectrometry., 2013, 34(24): 131-134. (in Chinese)

[81] XI M Y, LIU R, WU P, XU K L, HOU X D, LV Y. Atomic absorption spectrometric determination of trace tellurium after hydride trapping on platinum-coated tungsten coil., 2010, 95(2): 320-325.

[82] LIU R, WU P, XU K L, LV Y, HOU X D. Highly sensitive and interference-free determination of bismuth in environmental samples by electrothermal vaporization atomic fluorescence spectrometry after hydride trapping on iridium-coated tungsten coil., 2008, 63(6): 704-709.

[83] MATUSIEWICZ H, KRAWCZYK M. Determination of nickel by chemical vapor generation in situ trapping flame AAS., 2011, 9(4): 648-659.

[84] LIU M T, LIU T P, LIU J X, MAO X F, NA X, DING L, CHEN G Y, QIAN Y Z. Determination of arsenic in biological samples by slurry sampling hydride generation atomic fluorescence spectrometry using in situ dielectric barrier discharge trap., 2019, 34(3): 526-534.

[85] ZOU Z R, DENG Y J, HU J, JIANG X M, HOU X D. Recent trends in atomic fluorescence spectrometry towards miniaturized instrumentation-A review., 2018, 1019: 25-37.

[86] BERNHARD W, MARIANNE S J, MICHAEL S, DAVID L S, DAVID A R. Investigation of reactions and atomization of arsine in a heated quartz tube using atomic absorption and mass spectrometry., 1990, 45(11): 1235-1256.

[87] NA N, ZHANG C, ZHAO M X, ZHANG S C, YANG C D, FANG X, ZHANG X R. Direct detection of explosives on solid surfaces by mass spectrometry with an ambient ion source based on dielectric barrier discharge., 2007, 42(8): 1079-1085.

[88] NA N, ZHAO M X, ZHANG S C, YANG C D, ZHANG X R. Development of a dielectric barrier discharge ion source for ambient mass spectrometry., 2007, 18(10): 1859-1862.

[89] 劉美彤, 劉霽欣, 毛雪飛, 丁蘭. 介質(zhì)阻擋放電微等離子體在元素分析中的應(yīng)用研究. 農(nóng)產(chǎn)品質(zhì)量與安全, 2018(4): 18-24.

LIU M T, LIU J X, MAO X F, DING L. Application research of dielectric barrier discharge microplasma on elemental analysis.2018(4): 18-24. (in Chinese)

[90] KRATZER J, BOUSEK J, STURGEON R E, MESTER Z, DEDINA J. Determination of bismuth by dielectric barrier discharge atomic absorption spectrometry coupled with hydride generation: method optimization and evaluation of analytical performance., 2014, 86(19): 9620-9625.

[91] 毛雪飛, 齊悅涵, 王世光, 劉霽欣, 王敏, 錢永忠. 介質(zhì)阻擋放電在農(nóng)業(yè)領(lǐng)域的應(yīng)用研究進展. 農(nóng)業(yè)機械學(xué)報, 2016, 47(4): 216-227.

MAO X F, QI Y H, WANG S G, LIU J X, WANG M, QIAN Y Z. Review for application of dielectric barrier discharge in agriculture., 2016, 47(4): 216-227. (in Chinese)

[92] LI S P, MA X L, JIANG Y Y, CAO X H. Acetamiprid removal in wastewater by the low-temperature plasma using dielectric barrier discharge., 2014, 106: 146-153.

[93] GUSHCHIN A A, GRINEVICH V I, IZVEKOVA T V, KVITKOVA E Y, TYUKANOVA K A, RYBKIN W. The destruction of carbon tetrachloride dissolved in water in a dielectric barrier discharge in oxygen., 2019, 39(2): 461-473.

[94] TORMEN L, GIL R A, FRESCURA V L A, MARTINEZ L D, CURTIUS A J. The use of electrothermal vaporizer coupled to the inductively coupled plasma mass spectrometry for the determination of arsenic, selenium and transition metals in biological samples treated with formic acid., 2012, 717: 21-27.

[95] LI Y C, JIANG S J. Determination of Cu, Zn, Cd and Pb in fish samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry., 1998, 359(1/2): 205-212.

[96] ARAUJO R R O, OLESZCZUK N, RAMPAZZO R T, COSTA P A, SILVA M M, VALE M G R, WELZ B, FERREIRA S L C. Comparison of direct solid sampling and slurry sampling for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry., 2008, 77(1): 400-406.

[97] SAVIO M, CERUTTI S, MARTINEZ L D, SMICHOWSKI P, GIL R A. Study of matrix effects and spectral interferences in the determination of lead in sediments, sludges and soils by SR-ETAAS using slurry sampling., 2010, 82(2): 523-527.

[98] KATAOKA H, OKAMOTO Y, TSUKAHARA S, FUJIWARA T, ITO K. Separate vaporisation of boric acid and inorganic boron from tungsten sample cuvette-tungsten boat furnace followed by the detection of boron species by inductively coupled plasma mass spectrometry and atomic emission spectrometry (ICP-MS and ICP-AES)., 2008, 610(2): 179-185.

[99] KARANASSIOS V, ABDULLA M, HORLICK G. The application of chemical modification in direct sample insertion-inductively coupled plasma-atomic emission spectrometry.1990, 45(1/2): 119-129.

[100] 鄧勃. 石墨爐原子吸收光譜分析中化學(xué)改進技術(shù)的進展. 現(xiàn)代科學(xué)儀器, 2009, 1(1): 100-115.

DENG B. Recent development of chemical modification technique in graphite furnace atomic absorption spectrometry., 2009, 1(1): 100-115. (in Chinese)

[101] 朱霞石, 胡斌, 何蔓, 江祖成. 8-羥基喹啉在ETAAS和ETV-ICP- AES測定鉻形態(tài)中基體改進作用的比較研究. 分析科學(xué)學(xué)報, 2005, 21(1): 1-4.

ZHU X S, HU B, HE M, JIANG Z C. Comparative study on chemical modification of 8-oxin determination of Cr(Ⅲ)and Cr(Ⅵ)by ETAAS and ETV-ICP-AES.2005, 21(1): 1-4. (in Chinese)

[102] TSENG Y J, LIU C C, JIANG S J. Slurry sampling electrothermal vaporization inductively coupled plasma Mass spectrometry for the determination of As and Se in soil and sludge., 2007, 588(2): 173-178.

[103] DOBROWOLSKI R. Slurry sampling for the determination of thallium in soils and sediments by graphite furnace atomic absorption spectrometry., 2002, 374(7/8): 1294-1300.

[104] XIE Y C, TANG Y Q. Spontaneous monolayer dispersion of oxides and salts onto surfaces of supports: applications to heterogeneous catalysis.1990, 37: 1-43.

[105] SHUTTLER I, FEUERSTEIN M, SCHLEMMER G. Communication. Long-term stability of a mixed palladium–iridium trapping reagent for in situ hydride trapping within a graphite electrothermal atomizer., 1992, 7(8): 1299-1301.

[106] OLESZCZUK N, CASTRO J T, DA SILVA M M, KORN M D A, WELZ B, VALE M G R. Method development for the determination of manganese, cobalt and copper in green coffee comparing direct solid sampling electrothermal atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry., 2007, 73(5): 862-869.

[107] VALE M, SILVA M M, WELZ B, LIMA E C. Determination of cadmium, copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry., 2001, 56(10): 1859-1873.

[108] DA SILVA A F, BORGES D, LEPRI F, WELZ B, CURTIUS A, HEITMANN U. Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry., 2005, 382(8): 1835-1841.

[109] JIN L L, YUAN S S, LI M, XING Z, LIU Z F, HU S H. Dielectric barrier discharge atomizer for mercury speciation by HPLC-CVG atomic fluorescence spectrometry., 2019, 40(2): 69-73.

Technical Review of Fast Detection of Heavy Metals in Soil

MAO XueFei, LIU JiXin, QIAN YongZhong

(Institute of Quality Standard and Testing Technology for Agri-Products, Chinese Academy of Agricultural Sciences / Key Laboratory of Agri-Food Safety and Quality, Ministry of Agriculture and Rural Affairs, Beijing 100081)

Recently, with the high-speed development of industry and agriculture in China, the contamination of heavy metal has become a severe environmental problem caused by immoderate mining operation, "three wastes" emissions, vehicle exhaust, and misuse of agricultural chemical inputs. So, it is very important to monitor the contamination of heavy metals in soil. However, the national and industrial standards of detecting heavy metals in soil mainly focus on the traditional analytical approaches employed in laboratory at present. So, it is still difficult to achieve the on-site and fast detection of heavy metals in soil, which gives rise to such difficulty of monitoring and preventing the source contamination effectively and timely. In view of the matrix of soil sample, solid sampling analysis should be feasible to the fast detection of heavy metals, including electrothermal vaporization (ETV), X-ray fluorescence spectrometry (XRF), laser ablation (LA), laser induced breakthrough spectrometry (LIBS), X-ray photoelectron spectroscopy (XPS), and instrumental neutron activation analysis (INAA). The solid sampling techniques do not require digestion treatment and is thereby fast and efficient. However, among them, the detection limit and stability of XRF, LA, and LIBS cannot satisfy the all demands in standards of soil quality; on the other hand, it is too difficult to reach the miniaturization and on-site testing for LA, XAS, and INAA. By comparison, ETV is a kind of solid sampling tool with excellent advantages such as high analytical sensitivity, favorable stability, and being easy to be miniaturized, using electric heating to introduce analysesaerosol from the sample into the atomizer or exciter for measurement. ETV is able to introduce heavy metals fast and efficiently, which is versatile to atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), atomic emission spectrometry (AES), and induced coupled plasma mass spectrometry (ICP-MS). As usual, many materials such as carbon, metals, and quartz can be utilized for ETV, which are frequently processed into graphite furnace, porous carbon tube, tungsten coil, rhenium coil, quartz tube and so on. Among various ETV approaches, electromagnetic induction ETV is characterized with no cold zone, fast heating or cooling and miniaturization. Considering the complicated soil matrices, however, ETV has been always confronted with the bottleneck problem, namely matrix interference. Through integrating these advanced techniques including gas phase enrichment (GPE), dielectric barrier discharge, matrix modifier, background correction and so on, the matrix interference will be eliminated completely for the detection of heavy metals in soil when solid sampling by using ETV atomic spectrometers. Especially for GPE, it can realize both two aims at one time: eliminating matrix interference and improving analytical sensitivity. This review is about to bring some valuable suggestions for innovating the fast detection of heavy metals in soil, to play parts in the environmental monitoring and protection in the future.

soil; heavy metals; fast detection; electrothermal vaporization; solid sampling; matrix interference

2019-04-28；

2019-08-22

國家重點研發(fā)計劃（2017YFD0801203、2017YFF0108203）、國家自然科學(xué)基金面上項目（31571924）、中國農(nóng)業(yè)科學(xué)院基本科研業(yè)務(wù)費專項（Y2019XK05）

毛雪飛，E-mail：mxf08@163.com & maoxuefei@caas.cn。通信作者錢永忠，Tel：010-82106298；E-mail：qyzcaas@163.com。通信作者劉霽欣，Tel：010-82106540；E-mail：ljx2117@gmail.com

（責(zé)任編輯 李云霞）