祝銀+劉琴+楊承虎+王范盛+李子孟+宋凱
摘要 本文建立一種改進(jìn)的高效液相色譜-電感耦合等離子體質(zhì)譜法測(cè)定淡水中鉻形態(tài)的方法。通過樣品加標(biāo)回收驗(yàn)證本方法的準(zhǔn)確度,本方法Cr(Ⅲ)和Cr(Ⅵ)的回收率均在93%~115%之間。通過制備7個(gè)濃度水平確定得到鉻元素的校準(zhǔn)曲線范圍,Cr(Ⅲ)和Cr(Ⅵ)的相關(guān)系數(shù)接近1(r=0.999 9),Cr(Ⅲ)和Cr(Ⅵ)的LOD分別為0.094、0.100 μg/L,Cr(Ⅲ)的LOQ為0.28 μg/L,Cr(Ⅵ)為0.30 μg/L。綜上所述,方法的定量限、重現(xiàn)性和準(zhǔn)確度滿足淡水中Cr(Ⅲ)和Cr(Ⅵ)的定量分析,可以有效應(yīng)用于其預(yù)期的使用。
關(guān)鍵詞 形態(tài)分析;鉻形態(tài);飲用水;高效液相色譜-電感耦合等離子體質(zhì)譜法
中圖分類號(hào) O657.7+2;O657.63 文獻(xiàn)標(biāo)識(shí)碼 A 文章編號(hào) 1007-5739(2018)01-0174-02
Determination of Chromium Speciation in Drinking Water by RPIP-HPLC-ICP-MS
ZHU Yin 1,2 LIU Qin 1,2 YANG Cheng-hu 1,2 WANG Fan-sheng 1,2 LI Zi-meng 1,2 SONG Kai 1,2
(1 Marine Fisheries Research Institute of Zhejiang Province,Zhoushan Zhejiang 316021; 2 Key Lab of Sustainable Utilization of Technology Research for Fishery Resource of Zhejiang Province)
Abstract The approach presented in this paper refered to the modification of a method for the detection and quantitative determination of chromium species in water by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The accuracy of the method was verified by sample adding recovery estimation. The recovery rates of both determined analytes were between 93% and 115%.Calibration curve was obtained by preparing seven concentration levels of each chromium species. In both cases,the correlation coefficient was close to 1(r=0.999 9)for Cr(Ⅲ)and Cr(Ⅵ). Using the HPLC-ICP-MS method,LOD was 0.094 μg/L and 0.100 μg/L for Cr(Ⅲ)and Cr(Ⅵ),respectively. According to the modified blank determination method,LOQ for Cr(Ⅲ)was 0.28 μg/L and for Cr(Ⅵ)was 0.30 μg/L.As a result of the method validation experiment,the obtained limit of quantification,repeatability and intermediate precision were satisfied for the quantification of Cr(Ⅲ)and Cr(Ⅵ)in water matrices. The method can be applied effectively for its intended use.
Key words speciation analysis;chromium speciation;drinking water;HPLC-ICP-MS
鉻是硬度最大的金屬元素,化學(xué)符號(hào)Cr,廣泛分布于環(huán)境中,并且在工業(yè)中有許多應(yīng)用,例如電鍍與鋼鐵業(yè)[1]。在鉻的幾種存在形式中,Cr(Ⅲ)是人體必需的營(yíng)養(yǎng)物質(zhì),但Cr(Ⅵ)是劇毒,具強(qiáng)氧化性,并且極易滲透生物膜[2]。目前,歐盟飲用水中允許的總鉻含量是50 μg/L。國內(nèi)現(xiàn)行地表水的Cr(Ⅵ)根據(jù)不同的水域?qū)?yīng)不同限量值,Ⅴ類水質(zhì)限量為100 μg/L,Ⅱ類、Ⅲ類和Ⅳ類水質(zhì)限量均為50 μg/L,Ⅰ類限量為10 μg/L。
高效液相色譜-電感耦合等離子體質(zhì)譜技術(shù)(HPLC-ICP-MS)是測(cè)定水樣中鉻元素形態(tài)的良好分析手段。ICP-MS作為最靈敏的檢測(cè)器之一,具有元素特異性、寬線性動(dòng)態(tài)范圍和極低檢測(cè)限等優(yōu)點(diǎn)[3]。ICP-MS的動(dòng)態(tài)反應(yīng)池技術(shù)(DRC)極大地降低了40Ar12C+和35Cl16OH+的光譜干擾,從而提高了鉻元素分析的靈敏度[4]。鉻形態(tài)分析的色譜方法可能包括離子色譜(IC),離子對(duì)反相色譜(RPIPC)。RPIP-HPLC是廣泛使用的一種簡(jiǎn)單、靈活、靈敏的分離鉻化合物的方法。盡管在這一領(lǐng)域擁有大量文獻(xiàn),但尚未建立充分有效的方法,尤其是關(guān)于形態(tài)分析的可追溯性和不確定度測(cè)量的論證。本研究的目的是使用RPIP-HPLC-ICP-MS測(cè)定飲用水中Cr(Ⅲ)和Cr(Ⅵ),并對(duì)分析程序進(jìn)行詳細(xì)的驗(yàn)證。
1 材料與方法
1.1 儀器設(shè)備
ICP-MS:7900a型(USA,Agilent);HPLC:1220型(USA,Agilent)。色譜柱:Perkin Elmer C8(3.3 mm,3 μm);柱溫25 ℃;進(jìn)樣體積50 μL;流速1.2 mL/min;流動(dòng)相0.8 mmol/L TBAH,0.6 mmol/L EDTA,pH=6.9;洗脫程序?yàn)榈榷认疵摚豢傔M(jìn)樣時(shí)間3 min。質(zhì)譜條件RF 功率1 050 W;采樣深度7.8 mm;冷卻氣流量(Ar)13 L/min;等離子體氣流量(Ar)15 L/min;霧化氣流量(Ar)0.88 L/min;輔助氣流量(Ar)1.2 L/min;樣品提升速率0.8 mL/min;采集時(shí)間750 s;積分時(shí)間1 s;監(jiān)測(cè)質(zhì)量數(shù)(m/z+)為52Cr+;采樣錐和截取錐為Ni。
1.2 試劑材料
Cr(Ⅵ)標(biāo)準(zhǔn)儲(chǔ)備溶液1 000 mg/L,NSI;Cr(Ⅲ)標(biāo)準(zhǔn)儲(chǔ)備溶液1 000 mg/L,NSI;四丁基氫氧化銨(TBAH,美國Sigma-Aldrich 公司);乙二胺四乙酸(EDTA),分析純;硝酸,優(yōu)級(jí)純;甲醇,優(yōu)級(jí)純。
1.3 樣品處理
樣品收集在100 mL聚乙烯瓶中,并立即凍結(jié),在分析前除霜。樣品經(jīng)0.2 μm再生纖維素濾膜過濾。樣品與流動(dòng)相按體積比3∶1稀釋,保存在玻璃瓶中,室溫下1 h左右,形成(CrEDTA)-復(fù)合物。
2 結(jié)果與分析
2.1 線性范圍
用10 μg/L的標(biāo)準(zhǔn)溶液配置工作曲線(n=7),確定Cr(Ⅲ)和Cr(Ⅵ)的保留時(shí)間。通過分析極端濃度分析物的方差,確定工作曲線范圍,并根據(jù)文獻(xiàn)計(jì)算F值[5]。在本研究中,F(xiàn)值估計(jì)鉻元素校準(zhǔn)曲線的濃度限值為0.3、10.0 μg/L。可以得出結(jié)論,計(jì)算結(jié)果的方差在統(tǒng)計(jì)學(xué)上無顯著差異。因此,校準(zhǔn)曲線的選擇是正確的。制備7個(gè)濃度水平(0.3、1.0、2.0、3.0、5.0、7.5、10.0 μg/L)的點(diǎn)分別得到鉻元素的校準(zhǔn)曲線,Cr(Ⅲ)和Cr(Ⅵ)的相關(guān)系數(shù)接近1(r=0.999 9)。Cr(Ⅵ)的靈敏度高于Cr(Ⅲ)。
2.2 檢出限和定量限
檢出限(LOD)定義為可以可靠測(cè)量的最低濃度。這個(gè)值是由空白樣品-空白測(cè)定方法信號(hào)的標(biāo)準(zhǔn)偏差的3倍計(jì)算出來的[6-8]。在本研究中,使用了以下3種方法測(cè)定LOD:①改進(jìn)的空白測(cè)定方法?;趯?duì)可定量分析的空白樣本的測(cè)定:LOD=3 S。其中S表示鉻元素濃度為的0.5 μg/L時(shí)10個(gè)獨(dú)立測(cè)量值的標(biāo)準(zhǔn)偏差(n=3)[5,9]。②圖解法。基于3個(gè)標(biāo)準(zhǔn)溶液的標(biāo)準(zhǔn)偏差得到,根據(jù)公式LOD=3 S0(S0表示截距)計(jì)算Cr(Ⅲ)和Cr(VI)(n=6)濃度為0.3、0.4、0.5 μg/L時(shí)的標(biāo)準(zhǔn)偏差。③線性回歸方法?;谛盘?hào)的標(biāo)準(zhǔn)偏差和校準(zhǔn)曲線的斜率(標(biāo)準(zhǔn)偏差/斜率比)計(jì)算:LOD=3.3 S/b。其中,S表示表示信號(hào)的標(biāo)準(zhǔn)偏差(根據(jù)校準(zhǔn)曲線估計(jì)),b為校準(zhǔn)曲線的斜率[5,10]。定量限(LOQ)是分析物定量測(cè)定的最低濃度,可用精度和準(zhǔn)確度的可接受水平確定。在本研究中,計(jì)算為3倍LOD。采用HPLC-ICP-MS法,根據(jù)改進(jìn)的空白測(cè)定方法Cr(Ⅲ)和Cr(Ⅵ)的LOD分別為0.094、0.100 μg/L[Cr(Ⅲ)的LOQ為0.28 μg/L,Cr(Ⅵ)為0.30 μg/L]。因?yàn)樵趍/z+為52時(shí),鉻元素的LOD值為背景標(biāo)準(zhǔn)偏差的3倍(表1)。因此,得到的結(jié)果易于與其他比較。
2.3 精密度
精密度在重現(xiàn)性和中間精密度條件下確定,并通過分析加入了2 μg/L鉻元素標(biāo)準(zhǔn)溶液的飲用水進(jìn)行評(píng)估。重現(xiàn)性和中間精密度表示為變異系數(shù)(CV)。同一操作者在短時(shí)間內(nèi)使用相同的方法和設(shè)備測(cè)定重現(xiàn)性,在同一天重復(fù)測(cè)量上述水樣10次。對(duì)于Cr(Ⅲ)和Cr(Ⅵ),得到的結(jié)果分別為1.5%和1.6%。所得結(jié)果對(duì)應(yīng)于先前提出的值。
同一操作者在較長(zhǎng)時(shí)間內(nèi)用相同方法獲得的結(jié)果評(píng)估中間精密度,連續(xù)3 d從相同的加標(biāo)飲用水樣品中進(jìn)行測(cè)定。得到變異系數(shù)Cr(Ⅲ)為3.4%、Cr(Ⅵ)為3.5%,表明中間精密度良好。
2.4 準(zhǔn)確度
評(píng)價(jià)方法準(zhǔn)確度最常用的方式是使用特定標(biāo)準(zhǔn)物質(zhì)。本研究中,因?yàn)槿鄙龠m用于鉻形態(tài)分析的標(biāo)準(zhǔn)物質(zhì)[13,18-19],方法通過確定每個(gè)分析物的回收率來驗(yàn)證優(yōu)化分析過程的效率。將2種鉻元素添加到濃度為2.0 μg/L的4種不同水體基質(zhì)中,在飲用水加標(biāo)溶液中進(jìn)行的回收率結(jié)果見表2??梢钥闯?,提出的方法可以檢測(cè)水中存在的Cr(Ⅲ)和Cr(Ⅵ),并且低于WHO提出的水中總鉻含量。采集的樣品中檢測(cè)出鉻元素的回收率在93%~115%之間。結(jié)果表明,Cr(Ⅲ)和Cr(Ⅵ)的回收率在±10%之內(nèi)。加標(biāo)樣品回收率在加標(biāo)值±25%以內(nèi),則認(rèn)為可接受。該標(biāo)準(zhǔn)由美國EPA方法6020A推薦用于ICP-MS的元素分析,并在本研究中得到確認(rèn)。
3 結(jié)論
目前,鉻的形態(tài)分析主要是在環(huán)境樣品中進(jìn)行。HPLC-ICP-MS法使飲用水中Cr(Ⅲ)和Cr(Ⅵ)的檢測(cè)和量化快速、準(zhǔn)確。采用改良的空白測(cè)定法測(cè)定LOD,并將所得結(jié)果與其他研究人員所得的值進(jìn)行比較。在大部分鉻形態(tài)研究文獻(xiàn)中,LOD通常用最簡(jiǎn)單的方法計(jì)算,即背景的3倍標(biāo)準(zhǔn)偏差。每個(gè)元素的回歸系數(shù)為0.999 9,從而證明了該方法的線性和重現(xiàn)性。對(duì)加標(biāo)樣品的定量分析表明,2種鉻元素的回收率在93%~115%之間。
4 參考文獻(xiàn)
[1] KOTAS′ J,STASICKA Z.Chromium occurrence in the environment and methods of its speciation[J].Environ Pollut,2000(107):263-283.
[2] METZE D,JAKUBOWSKI N,KLOCKOW D.Speciation of chromium[M]//CORNELIS R,CREWS H,CARUSO J,et al.Handbook of elemental spe-ciation II:Species in the environment,food,medicine and occupational health. New York:Wiley,2005.
[3] WROBEL K,CARUSO JA.Elemental and isotope ratio mass spectrometry [M]//GROSS M L,CAPRIOLI R M.The encyclopedia of mass spectrometry,Volume 5:elemental and isotope ratio mass spectrometry.Oxford:Elsevier,2010.
[4] EIDEN G,BARINAGA C J,KOPPENAAL D W[M]//GROSS ML,CAPRI-OLI RM.The encyclopedia of mass spectrometry,Volume 5:elemental and isotope ratio mass spectrometry. Oxford:Elsevier,2010.
[5] KONIECZKA P,NAMIES′NIK J.Quality assurance and quality control in the analytical chemical laboratory[M]//A practical approach. Boca Raton:Taylor & Francis Group,2009.
[6] KUO CY,JIANG SJ,SAHAYAM AC.Speciation of chromium and vanad-ium in environmental samples using HPLC-DRC-ICP-MS[J].J Anal At Spectrom,2007(22):636-641.
[7] CHANG Y L,JIANG S J.Determination of chromium species in water samples by liquid chromatography-inductively coupled plasma-dynamic reaction cell-mass spectrometry[J].J Anal At Spectrom,2001(16):858-862.
[8] NEUBAUER K,REUTER W,PERRONE P.Chromium speciation in water by HPLC/ICP-MS:Application Note[Z].Norwalk:Perkin Elmer,2003.
[9] EURACHEM GUIDE.The fitness for purpose of analytical methods:a laboratory guide to method validation and related topics[Z].Teddington:LGC,1998.
[10] GU¨RLEYU¨KH,WALLSCHLA¨GERD.Determination of chromium(III)and chromium(VI)using suppressed ion chromatography inductively coupled plasma mass spectrometry[J].J Anal At Spectrom,2001(16):926-930.
[11] XING L,BEAUCHEMIN D.Chromium speciation at trace level in potable water using hyphenated ion exchange chromatography and inductively coupled plasma mass spectrometry with collision/reaction interface[J].J Anal At Spectrom,2010(25):1046-1055.
[12] International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use. ICH Guideline Q2(R1):validation of analytical procedures:text and methodology[EB/OL].[2013-02-12].http://www.ich.org/.
[13] CHEN Z L,MEGHARAJ M,NAIDU R.Removal of interferences in the speciation of chromium using an octopole reaction system in ion chromatography with inductively coupled plasma mass spectrometry[J].Talanta,2007(73):948-952.
[14] WOLF R E,MORRISON J M,GOLDHABER M B.Simultaneous determi-nation of Cr(III)and Cr(VI)using reversed-phased ionpairing liquid chromatography with dynamic reaction cell inductively coupled plasma mass spectrometry[J].J Anal At Spectrom,2007(22):1051-1060.
[15] WANG HJ,DU XM,WANG M,et al.Using ion-pair reversed-phase HPLC ICP-MS to simultaneously determine Cr(III)and Cr(VI)in urine of chromate workers[J].Talanta,2010(81):1856-1860.
[16] VANHAECKE F,SAVERWYNS S,DE WANNEMACKER G,et al.Comparison of the application of higher mass resolution and cool plasma conditions to avoid spectral interferences in Cr(III)/Cr(VI)speciation by means of high-performance liquid chromatography-inductively coupled plasma mass spectrometry[J].Anal Chim Acta,2000(419):55-64.
[17] SE′BY F,CHARLES S,GAGEAN M,et al.Chromium speciation by hy-phenation of high-performance liquid chromatography to inductively coupled plasma-massspectrometry:study of the influence of interfering ions[J].J Anal At Spectrom,2003(18):1386-1390.
[18] XIE Q,KERRICH R,IRVING E,et al.Determination of five arsenic sp-ecies in aqueous samples by HPLC coupled with a hexapole collision cell ICP-MS[J].J Anal At Spectrom,2002(17):1037-1041.
[19] CASTILLO A,ROIG-NAVARRO A F,POZO O J.Capabilities of microbore columns coupled to inductively coupled plasma mass spectrometry in speciation of arsenic and selenium[J].J Chromatogr A,2008(1202):132-137.