Determination of trace multi-elements in coal fly ash by inductively coupled plasma mass spectrometr

J Cent. South Univ. Technol. (2007)01-0068-05DO10.1007/s11771007-0014-32 SpringerDetermination of trace multi-elements in coal fly ash byinductively coupled plasma mass spectrometryXIE Hua-lin(谢华林}2, TANG You:gen(唐有根), LI Yu-jie(李玉杰), LI Li-bo(李立波)2(1. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China;2. Department of Chemistry, Hunan Institute of Technology, Hengyang 421008, China)Abstract: The contents of Cr, Cu, Ni, As, Cd and Pb in coal fly ash were determined by a high resolution inductively coupled plasmamass spectrometry method. The sample digestions were performed in closed microwave vessels with HNO3, HCIO4 and HF.Theptimum conditions for the determination were obtained. The applicability of the proposed method was validated by the analysis ofcoal fly ash reference material (NIST SRM 1633a). The results show that most of the spectral interferences can be avoided bymeasuring in the high resolution mode(maximum mass resolution R-9 000). The detection limit is from 0.05 to 0.21 ug/g, and theprecision is fine with relative standard deviation less than 4.3%.Key words: coal fly ash; microwave digestion; inductively coupled plasma mass spectrometry; determinationHigh resolution inductively coupled plasma mass1 Introductionspectrometry(HR-ICP-MS)is capable of resolving manyplasma, water-, and matrix-based polyatomicCoal contains large amounts of metallic elements. interferences, and the technique has been used for theThe determination of trace elements in coal fly ash successful determination of elements which subject toamples is important with respect to health and spectral interference in complex matrices/ 4). HR-ICPenvironment. Thus, a sensitive, rapid and reliable MS is characterized by its high sensitivity, low detectionanalytical method for analysis of trace elements in coal limits, and the possibility of separating analytic signalsfly ash is required. Several analytical techniques, from spectral interferences using higher mass resolutionincluding atomic absorption spectrometry (AAS) techniques"51methods-3,inductively coupled plasma atomicIn this study, a microwave-assisted digestionemission spectrometry(ICP-AES)7, neutron activation procedure for dissolution of coal fly ash samples wasX-ray fluorescence spectrometry investigated and the contents of Cr, Cu, Ni, As, Cd andXRF)0, and inductively coupled plasma mass Pb were determined by HR-ICP-MSspectrometry(ICP-MS)-14) have been applied for traceelemental determination in coal fly ash samples. ICP-Ms 2 Experimentalhas emerged as one of the favored methods due to itsunique combination of low detection limits, wide 2.1 Instrumentsdynamic range, capabilities for rapid multi-elemental anda Micromass Plasma Trace 2 HR-ICP-MSisotopic determination. However, in spite of many (Micromass Ltd, Manchester, England)was used for theadvantages of quadrupole based ICP-MS, it still suffers determination of trace elements. The instrumentalfrom spectral interferences due to overlaps of atomic and parameters were as follows: power 1.45 kW, coolant gasmolecular ions. As complete digestion of coal fly ash flow 14.5 L/min, auxiliary gas flow 0.9 L/min, nebulizersample requires perchloric acid, the determination of As gas flow 1.2 L/min, sampling cone nickel(1.1mmand Cr by quadrupole ICP-MS (ICP-QMS)is susceptible orifice diameter), skimmer cone nickel( 0.8 mm orificeto being interfered byArCl3CIOH, andCI0 at diameter), ion sampling depth 11 mm, sample uptake rateAs, Cr, and >Cr, respectively. An alternative of 0. 25 mL/min, dwell time 20 ms, accelerating voltage 6ICP-QMS cannot resolve isobaric interferences at the kv, remasses of As and Cr. ICP-QMS is difficult to the madifferentiate analyte ions and interring polyatomic ionsYH中国煤化工djusted to obtainCNMH GCEM Corporationtion item: Project(04JJ40016) supported by the Natural Science Foundation of Hunan Province, China20060423; Accepted date:2006-0615pondingauthor:TANGYou-gen,Professor:Tel:+86-731-8830886;E-mail::ygtang@mail.csu.edu.cnXIE Hua-lin, et al: Determination of trace multi-elements in coal fly ash by ICP-MSUSA)was used for sample digestion. A peristaltic pump consequence, the sensitivity is reduced to a certain(MP-32, Tokyo Rikakikai, Tokyo, Japan)was used to extent. Therefore, to measure the trace elements, suitableregulate the flow rates of the carrier solutionsmass resolution should be chosen to separate analyte ionpeaks from interfering polyatomic ion2. 2 Standard solution and reagentsmeasured peaks to determine contents in the samplesUltrapure water from a Milli-Q deionization unit isotopes whose abundances are maximum, or isotopes(Millipore, Milli-Q SP)was used throughout the which are not overlapped by the polyatomic or doublyexperiment. Single element calibration solutions were charged ion peaks of matrix elements and Ar.Theprepared from I g/L stock solutions of Cr, Cu, Ni, As, Cd isotopes determined are listed in Table 1and Pb in 10% HNO, by dilution with ultrapure waterThe same procedure was followed for the preparation of Table 1 Isotopes, resolution, detection limits and blank testthe working solution to be used as the internal standard Isotope Resolution Detection limit/ Blank value/for mass spectrometric determinations. Multi-elementug g (ug gstandard solutions were prepared from single element0.120.15stock solutions. These solutions were freshly prepared<007Reference material SRM 1633a was used to study theaccuracy.9000The acids used to digest samples were high-purityconcentrated HNO,, HCIO4 as well as HF, respectively<0.03High-purity H3 BO3 was employed to neutralize HF in thesolutions produced after the digestion of samples anddecomposition of fluorides. All glass and plastic waresIn ICP-MS, isotopes of all but two(Cd and Pb)ofwere cleaned by immersion in concentrated HNO, and the elements determined may suffer from interferencescaused by polyatomic ions resulted from the plasma gas,concentrated HCl overnight, then steamed successively entrained atmospheric gases, water and acid. The Cd andwith HNO3 and water vapor for & hPb ion peaks without being overlapped by the interfering2.3 Analytical proceduresion peaks were measured at m/Am=400. The analyte ionMicrowave digestion was adopted for sample peaks of Cr, Cu, Ni and As overlapped by polyatomicpreparation. About 0. 1 g sample of coal fly ash was ion peaks at m/Am=400. No visible interferences wereaccurately weighed and transferred into Teflon vessel,found in the vicinity of Cu peak at m/Am=3 000. Thefollowed by adding 3 mL HNO3, 3 mL HCIO4 and 2 mL other analyte ion peaks can be separated fromHE 3 mL H3 BO3 was added for buffering The digestion polyatomic ion peaks at m/Am=5 000 to m/Am=9000 onprogram was as followscalculation. The mass resolutions used are listed inFirst, the samples were digested with HNO,+ Table IHC104+HF at microwave power of 300 w for 8 minThe overlapping of Cr with"Ar?C and3C1 OHfollowed by 600 W for 10 min and 450 W for 4 mindicated in coal fly ash is shown in Fig. l, which mightsecondly H3BO3 was added into the solution at be caused by the decomposition of the sample bymicrowave of 300 w for 2 min and then at 600 w foraddition of HCIO4. It is very difficult to remove theminchlorine ions in the digested samples. If low resolutionOn cooling at room temperature the vessels were ICP-MS is used, the interference of 4Ar'2C on the 5Cropened, the mixtures were filtered and then diluted to will be significant 4. The interference from Ca 0 on50 mL with ultrapure water. The solution was further Ni is an example of spectral interferences in lowdiluted twice with ultrapure water so that the content of resolution ICP-MS for the remainder of the coal fly ashthe total dissolved salt(TDS)was about 0.1%, and the with a high concentration of Ca. Cr andNi weresolution was injected into the HR-ICP-MS. A blank measured at m/Am=5 000 Fig. 2 shows the peaks of'reagent was also prepared in the same way(100entering40△r35 Cl obtained at m/△m=中国煤化工 f75 is th3 Results and discussiononlyCN Gination of As. Theoverlapping does not affect the determination of As in3.1 Spectral interferencescoal fly ash because the concentration of As is highThe increase of the mass resolution leads toTherefore, HR-ICP-MS provides a more effectivereduction of the number of transmitted ions, as a and straightforward means to overcome the majority ofUniv. TechnoL. 2007, 14(1)spectral interferences using the high resolution modintensities of the three elements(1 ug/L)influenced byis sufficient to resolve the analyte signal from interfering the TDS are shown in Fig3I- Coal fly ash2-100 Hg/L Cr solution40-0204050080.1051905192519451.9651985200w(TDS)%Relative atomic massFig. I Mass spectra of Cr obtained by HR-ICP-MSCoal fly ash100 ug/LAs solution200.020.040.060.080.10BArCIw(TDS)%74.91Relative atomic massFig 2 Mass spectra of As obtained by HR-ICP-MS403.2 Non-spectral interferencesNon-spectral interference is another problem inCP-MS. Matrix effect resulted from the co-existingmatrix element leads to signal suppression orenhancement for the elements In order to evaluate the0020.040.060.080.10influence of non-spectral interferences on thedetermination of trace elements by HR-ICP-MSFig3 Sensitivity of three intermal standard elements in SRMmatrix effects should be corrected using internal standard1633a as function of TDS contentelements. If the matrix effects for internal standard(a) Low-resolution mode; (b) Medium-resolution modeelements agree with those for analyte elements, these(c)High-resolution modematrix effects can be corrected. It was reported thatfortrix effect wasusing internal standard elements with relative atomic intensities of the three elements gradually decrease withmass close to those of the analyte elements 7,Y, 0 Rh increasing the content of TDS. The respective sensitivityand In were selected to test respectively. These of 0.1elements are frequently used as intemal standards for about中国煤化工In is decreased bymedium-resolutiondrift correction in mass spectrometric measure-modeCNMHGmilar period, thments8-2. Five kinds solutions were prepared with sensitivity of the three elements gradually decreases withSRM 1633a controlling the content of TDS in mass increasing TDS content in the low-resolution modefraction range from 0.02%to 0.10%(0.02%, 0.04%,(m/Am=400)and high-resolution mode(m/Am=9 000)0.06%, 0.08% and 0.10%). The ion peak relative The optimum internal standard elements cannot be foundXIE Hua-lin, et al: Determination of trace multi-elements in coal fly ash by ICP-MSTherefore. it is difficult to correct the matrix effectsusing internal standard elements. So the standard Table 3 Contents of elements in three natural coal fly ashaddition method was used for each sample throughoutthis study.RSD/%Ele-Samplement3.3 Detection limits and blanksBThe detection limit was estimated as the analyte Cr 651#17 857#19 336#10 2.6 3.0concentration corresponding to three times the standard Cu 1623+291256+15 2447+59 1.22.4deviation(3o) of the blank signals obtained in the Ni86±3163±3213±73replicate measurements(n=10). The detection limits for±2272±3193±31analyte elements and blank tests are shown in Table IThe detection limits obtained by HR-ICP-MS are belowCd124±3206±8158±4243.9250. 1 ug/g for most elements. The results of blank tests forPb5572±751370±42681±16133.123all the elements are below the detection limits but Crindicating that the samples are treated without any 4 Conclusionssignificant contaminationD)A novel and reliable method for simultaneousIn order to validate the HR-ICP-MS method, the HR-ICP-MS after microwave dissolution is establish ia3.4 Analysis of SRM 1633adetermination of trace elements in coal fly ash usingcontents of Cr, Cu. Ni. As, Cd and Pb were determine2)HR-ICP-MS is not only a powerful diagnosticin the SRM 1633a sample. The analytical results for the tool for determining and resolving spectroscopicSRM 1633a standard sample together with certified interferences, but also a versatile technique forvalues are listed in Table 2, showing that for Cu, Ni, As, quantitative determination of analytes in low", medium-,Cd and Pb, the measured contents are in good agreement and high-resolution modes. The measured values are inwith the certified values. The relative standard deviations good agreement with the certified values, indicating that(RSDs for all elements of the observed values are within the accuracy is adequate for the determination of these5%. These results indicate that the present methodelementsprecise enough to apply to the multielement analysis of3)HR-ICP-MS may provide a better altermative forthe coal fly ash samplesmeasuring trace elements in coal fly ash because ofshorter analytical time and less contaminationTable 2 Analytical results for coal fly ash reference material(SRM 1633a) determined by HR-ICP-MsReferencesMob" RSD/ McerRelativeElement(ugg) (ugg") variance" [1 MESTER Z, ANGELONE M, BRUNORI C, et al.DigestionCr19300±3001.6196.00±040-1.5spectrometry[]. Anal Chim Acta, 1999, 395(1/2): 157-163.[2] HORVAT M, LUPSINA V, PIHLAR B. Determination of totalCu11500±4003.511800±300-2.5mercury in coal fly ash by gold amalgamation cold vapour atomicNi130.00±1000.8127.00±400+24absorption spectrometry[]. Anal Chim Acta, 1991, 243: 71-793] ZHANG D Q, NI Z M, SUN H W. Direct determination ofAs139.00±60043145.00±1500-41parts-per-billion levels of germanium in botanical samples and coal1.03±0.043.91.00±0.15+3.0fly ash by graphite fumace atomic absorption spectrometry(J)Fresenius J Anal Chem, 1997, 358(5): 641-645Pb73.60±0901.27240±040+1.7[4] NADLARNI R A. Applications of microwave oven sampleI)Mean value+ SD(standard deviation), n=5; 2)[(Mobr-MeeMoe]X%,dissolution in analysis[J]. Anal Chem, 1984, 56(12): 2233-2237.bere Mos and Mcer are observed and certified values, respectively[5] BETTINELLI M, BARONI U, PASTORELLI N Analysis of coal flyash and environmental materials by inductively coupled plasma3.5 Analysis of natural samplesdecomposition procedures[]. J Anal Atom Spectrom, 1987, 2(5):Table 3 shows the analytical results obtained fc485-489three natural coal fly ash samples from different power (61 D山中国煤化工 ELLINMicrowave ovenstations in China by using HR-ICP-MS. Each result isironmental and biologicalhe average of five sample determinations. As aCNMHGS9-174[7] RILEY K W, GODBEER W C. Acid extraction of coal for theconsequence the concentration in each sampledetermination of major ash forming elements]. Analyst, 1990different. The three samples contain comparatively highl15(6:865-867contents of all elements[8 NORTON G A, MALABY K L, DEKALB E L. ChemicalJ Cent. South Univ. Technol. 2007, 14(1)haracterization of ash produced during combustion ofinductively coupled plasma mass spectrometry (HR-ICPMS)refuse-derived fuel with coal[J]. Environ Sci Technol, 1988, 22(9)determination and multivariate evaluation of 10 trace elements in1279-1283mussels from 7 sites in Limfjorden, Denmark[]. Fresenius JAnal[9] WINBURN R S, GRIER D G, MCCRRTHY G J, et al. Rietveldhem2000368(7:708-714quantitative X-ray diffraction analysis of NIST fly ash standard [16] RODUSHKIN L Capabilities of high resolution inductively coupledreference materials). Powder Diffraction, 2000, 15(3): 163-172.plasma mass spectrometry for trace clement determination in plant[10] FURUYA K, MIYAJIMA Y, CHIBA T Recovery of uranium frommple digests[]. Fresenius J Anal Chem, 1998, 362(6): 541-546nuclear fuel scrap[J]. Environ Sci Tech, 1987, 21(9): 898-903[17 VANHAECKE F, VANHOE H, DAMS R, et al. The use of internal[11] LIU H T, JIANG S J. Determination of copper in coal fly ash in thestandards in ICP-MSU) Talanta, 1992, 39(7): 737-742.presence of excess titanium by dynamic reaction cell inductively [18] Das A K, chakRaBoRTY R, de la GUARDIA M, et al. ICP-MSupled plasma mass spectrometry[]. Anal Bioanal Chem, 2003multielement determination in fly ash after microwave-assisted375(2):306-309digestion of samples[]. Talanta, 2001, 54(6): 975-981[12] LIAO H C, JIANG S J. Determination of cadmium, mercury and [19] YU LL, VOCKE R D, MURPHY K E, et al. Determination of As,lead in coal fly ash by slurry sampling electrothermal vaporizationCd, Cr, and Hg in SRM 2584(trace elements in indoor dust) by highinductively coupled plasma mass spectrometry[]. Spectrochim Actasolution inductively coupled plasma mass spectrometry(J).Part E,199954(8):1233-1242Fresenius J Anal Chem, 2001, 370(): 834-837.[13] JACKSON B P, MILLER W. Arsenic and selenium speciation in [20] RODUSHKIN L, ODMAN F, BRANTH S Multielement analysis ofcoal fly ash extracts by ion chromatography- inductively coupledwhole blood by high resolution inductively coupled plasma massplasma mass spectrometry[]. J Anal Atom Spectrom, 1998, 13(10)spectrometry []. Fresenius J Anal Chem, 1998, 364(4): 338-34607-1112[21] TURK G C, YU L L, SALIT M L, et al. Using high-performance[14] RIONDATO J, VANHAECKE F, MOENS L, et al. Determination ofpectrometric methods for calibration transfer betweentrace and ultratrace elements in human serum with a double focusingenvironmental CRMs[]. Fresenius J Anal Chem, 2001, 370(2/3)magnetic sector inductively coupled plasma mass spectrometry[J]. J259-263.Anal Atom Spectrom, 1997, 12 (9): 933-937(Edited by CHEN Wei-ping)[15] BECHMANN IE, STURUP S, KRISTERSEN L V High resolution中国煤化工CNMHG