Chern. Anal. (Warsaw), 46,305 (2001) REVIEW

MicrowaveInduced. Plasma Emission Spectrometryfor Environmental Analysis. A Review*

by Krzysztof Jankowski

Department o/Analytical Chel11istry, Facultyo/Chemistry, Technical University o/Warsaw,3 Noakowskiego Str., 00-664 Warszawa, Poland

Key words: microwave induced plasma, environmental analysis, speciation

Microwave induced plasma is included among the new generation of spectrochemicalexcitation sources, which in therecent twenty years considerably broadened the possibil-ities of trace analysis and speciation studies. Analytical problemsconnected with envi-ronmental control and protection are the main field of applications ofatomic emissionspectrometry with the use ofmicrowave plasma(MIP-AES). A critical evaluation oftheusability ofthe MIP-AES method for multi-element analysis ofenvironmental samplesis presented. The analytical performance of this method considering various sample in-troduction techniques is shown. Examples of application of microwave. plasma. in theanalysis ofspecific environmental materials and also in speciation studies oftoxic heavymetal compounds are described.

Mikrofalowo indukowana plazma jest zaliczana do spektrochemicznych zr6del wzbu-dzenia nowej generacji, kt6re w ostatnich dwudziestu latach znacznie poszerzyly mozli-wosci analizy sladowej i badania specjacji.G16wnym obszarem zastosowan emisyjnejspektrometri( atomowej z uzyciem plazmy mikrofalowej (MIP-AES) s~ zagadnieniaanalityczne zwictzane z kontrol~ i ochron'l srodowiska. Przedstawiono krytyczn~ ocen~przydatnosci metody MIP-AES do analizy wielopierwiastkowej pr6bek srodowisko-wych. Zaprezentowano charakterystyk~ analityczn~ tej metody uwzgl~dniaj~c r6znetechniki wprowadzania pr6bek do plazmy. Opisano przyklady zastosowania plazmymikrofalowejw analizie konkretnych materia16w srodowiskowych, a takze w badaniachspecjacji toksycznych zwi~zk6wmetali ci~zkich.

*Presented at the VI Polish Conference on Analytical Chemistry, 9-14 July, 2000, Gliwice, Poland.

306 K. Jankowski

Atomic spectrOlTIetry based on absorption or emission of electromagnetic radia-tion by the atomized sample or on fluorescence are widely applied in environmentalstudies [1-3]. Among them, plasma atomic emission spectrometry plays an importantrole. This method, due to high sensitivity and specificity, and first of all versatilityand possibility of multielement analysis, is one of the lTIOst effective methods inchemical analysis. Due to the possibility of simultaneous determination ofmany ele-lnents and efficiency reaching several tens of determinations per hour, it is appropri-ate for monitoring the environment. A broad linear dynamic range for a large numberof elernents, enables silnultaneous determination of analytes at the ultra and microtrace level. Plasma sources ar~ characterized by high excitation efficiency, and atsame time by high stability, which results in a very sensitive and precise anal.yticalmethod.

Inductively coupled plasma atomic emission spectrometry (ICP-AES) is knownas a reliable and rapid method for multielement analysis, due to low detection limits,and appropriate, for the determination of practically all elements in environmentalsamples [4,5]. A different mechanism of the sample excitation inmicrowaveplaslnabased on Penning ionization with argon or helium metastables provides favorableconditions for the determination ofnon-metals, such as sulfur, nitrogen, phosphorus,chlorine and fluorine. In this sense ICP and MIP may be treated as supplementingeach other. There are reports on devices equipped simultaneously in both types ofplasma [6,7]. An important disadvantage having an essential effect on the extent ofapplication of lnicrowave plasma is the lack of commercially available instrumentsequipped with this excitation source. An apparatus ofHewlett-Packard in which MIPwas used as a universal and very sensitive detector in gas chromatography is an ex-emption here [8-11].

A great progress occurred in recent years in the field on Inicrowave inducedplasma [12-14] .• With the' aid of MIP over 70 elements at the trace level (detectionlimit 0.1 to 1000 ppb) can be determined. The ability to detect halogens at the ppblevel under the conditions of chromatographic analysis is a unique feature of heliummicrowave plasma in comparison to other types ofplasma. Microwave plasma can besustained in various gases such as argon, helium, nitrogen [15,16], air [16],oxygen[17], carbon dioxide [18], both under normal as well as reduced pressure, whichbroadens the possibility ofselecting appropriate measuring conditions and permits toanalyze samples of various origin, both inorganic and organic. The simplicity in de-sign ofMIP sources and low use ofenergy and gas are decisive for the low apparatusand operating costs ofMIP in comparison with other plasma excitation sources.

Analytical problems connected with the environment control and protection arethe main field of applications of the atomic emission spectrometry with microwaveplasma (MIP-AES). It finds application in the analysis of air and drinking water, soiland sediments, and also of biological materials. By selecting an appropriate experi-Inental setup the MIP-AES can be utilized for the determination ofthe total content ofelements in a sample [12], identification and determination of various chemical

Microwave induced plas111a emission spectroT11etry 307

forlTIsofone elelnent [11], or finally to deterlnine the structure ofmacrolnolecules ofnatural origin [19].

MIP exhibits the greatest analytical possibilities as coupled with salnple intro-duction techniques, which assure separation ofthe analyte froin the matrix and its in-troduction to plaslna in the forin of vapour. The number of applications of thehyphenated technique GC-MIP-AES in trace. analysis of real materials .and spe-ciation studies •rapidly increases [20,21]. Considerable analytical possibilities areprovided by coupling MIP with the.hydride generation [22] or electrotherlnal vapor-ization [23].

The lhnitations oflnicrowave plasma are connected mainly with the instability ofthe discharge caused by the introduction of the salnple lnaterial. It was found thatInaxilnuln lIng Inin-1 ofthematerial canbe introducedinto the plasma [24]. In recentyears several original resonator designs improving the MIP performance have beenproposed. The improved versions ofBeenakker's cavity [25,26], sufratons [27], Mi-crowave Plaslna Torch [28], or TE IOI rectangular cavity [29,30] perinit obtaining astable discharge even when introducing arelatively large ainount ofthe sample (val-ues froln? to 200 lng Inin-1 of water have been reported) [17,26,31l

Recently an increasing nUlnber ofMIP application in the analysis of agricultural[32,33], clinical [35,36] and industrial materials [37-39] are noted.

BASIC ASPECTS OF MIP-AES APPLICATION

The MIPcould be used as a source of sample excitation and atomic einission forthe Inultielement analysis, where depending on the form ofth.e sainple studied, vari-ous ways ofits introdllction are applied. In the second group ofapplication, MIP as at-oinizer, was applied in atoinic absorption spectrometry [40-42], atomic fluorescence[43-46] and especially Inass spectrometry [47-49]. The application of low-energylnicrowave piasina for fragmentation of large organic molecules in order to studytheir structure bY.Inass spectrometry [50] is an interesting example.

An ilnportant advantageofMIP-AES is its compatibility with various salnple in-troduction techniques. The operating parameters of microwave excitation sources,and especially the gas and analyte flow rates are similar to those applied in varioustypes of chrolnatography, hydride generation, graphite furnace, or flow injectionanalysis. Especially GC-MIP has an established position in trace analysis andspeciation studies [51-54]. This technique is utilized for the analysis oftrace ainountsof organic cOlnpounds containing heteroatoms, such as N, S, CI, Br, F, P, Si andorganometallic cOlnpounds [10,11]. High sensitivity and selectivity of detectiontakes advantage ofhigh resolution ofthe chromatographic separation. For lnany ele-mentsthe pg S-1 detection is achieved, and defined as the absolute detection lilnit di-vided by the elelneni peak half width. Absolute detection lilnit is defined as thealnountofeleluent (in pg) introduced on the .gas chromatographic coltunn, which pro-

308 K. Jankowski

duces an output signal equal to twice the background noise. The atomic emissionspectroinetry with Inicrowave piasina was applied also as a detection method in liquidchroinatography [55-59], capillary electrophoresis [60] and flow injection analysis[61].

Gas sainpies are introduced to the piasina after mixing with the piasina gas[62-64]. The deterinination ofnitrogen, oxygen, hydrogen, heliuln, krypton, amiTIO-nia, water vapour, carbon oxide and organic gases in argon can be an exainple. Thegas sample was introduced directly to the piasina gas streaITI by Ineans of a syringe.The detection lilnits permit direct analysis of argon of 5.5 N purity.

The analysis of liquid sainpies introduced by nebulization.is carried out Inainlyfor aqueous solutions [26,65,66]. However, the direct introduction of aqueous-organic [67] or organic [25, 61] solutions to the microwave piasina have also been re-ported. In the case ofsolid or liquid samples often conversion ofthe eleinent detectedto a volatile forin is applied, sOlnetilnes achieving also separation of the analyte froinother cOlnponents of the sample. Such techniques cover electrotherinal vaporization[23,68], especially irivolving a graphite furnace, hydride generation [22,69-71], coldvapour generation for Inercury [72,73] and other Inethods consisting in convertingthe detected eleinent into volatile halogens [74], carbonyls [45,75] or Inetal chelates[76], and in the case of non-InetaIs into volatile cOlnpounds such as chlorine, hydro-gen brolnide, sulfur dioxide or hydrogen sulfide [77-79].

Various sample introduction techniques are applied, in which no chemical modi-fication of the salnple occurs. Spark generation [37] or laser ablation [80] were usedfor the vaporization of solid salnples. Gelhausen and Carnahan [81] analysed coalsalnples by direct powder inj ection into He-MIP. Matusiewicz and Sturgeon [82] usedpneulnatic nebulization for slurry introduction of finely ground biological referenceInaterial dispersed in 10% nitric acid. Laylnan and Hieftje [83] suggested a Inicro arcfor the vaporization of salnples. A 0.1 to 40 f.ll salnple of the solution was placed onthe cathode, the solvent was evaporated, and the residue was atomized by an arc dis-charge.

Plaslna sources show variation with respect to the sainple excitation. The ICP is avery efficient excitation source, which leads to a very rich spectrlun, including in-tense ionic lines of many elements. The ICP spectrum is similar to that forlned in aspark discharge. However, the MIP spectrlun is siInilar to the arc spectruln with an ex-cess of atolnic lines and relatively slnall nUlnber of intense lines for particular ele-Inents, due to the slnaller excitation energy. The following order can be proposed inrespect of the degree of ionization:

spark> ICP» MIP ~ ncp > arc

Basic studies ofMIP spectra are still randoln and incolnplete [13, 66,84]. Spectraof a large group of eleinents excited in MIP have been recorded and the Inost intenselines have been chosen [85]. On the basis of data collected in Table 1 essential differ-

Microwave induced plasl'rla elnission spectro111etry 309

ences between Ar-MIP and Ar-ICP can be noticed. The ion lines ofTI and V,whichin ICP are the Inost intense lines ofthese elements, were not found in MIP. The inten-sity ofthe ion lines oiCd, Co, Cr, Hg, In, Mn, Ni, Pb and Pt is also Inuchsmaller inMIP than that in ICP [86,87]. For 18 of 50 elements presented an atoinic line is themost sensitive in MIP whereas the ionic one in ICP. However, for 20 of the eleinentsexactly the saIne line is reported as the Inost sensitive in MIP and ICP. ForAs, C, Ga,In, Mn, as, Pb, Re and V the Inost sensitive atoinic line in MIP is attributed to a transi-tion of lower energy than in ICP.

Table 1. The most intense atom and ion lines of some eletnents in the Ar-MIP and Ar-ICP (190-800 nn1)[13,85-88]; n.f. - not found; the most intense line of each element in MIP and ICP is underlined.

MIP-AES ICP-AES

Elelnent Atom line Ion line Atom line Ion linenm nn1 nn1 nm

Ag 328.07 n.f. 328.07 243.78

Al 396.15 n.f 309.27 281.62

As 234.98 n.f. 193.70 n.f.

Au 242.80 208.21 242.80 208.21

B 249.77 n.f. 249.77 n.f.

Ba 553.55 455.40 553.55 455.40

Be 234.86 313.04 234.86 313.04

Bi 223.06 n.f. 223.06 190.24

Br 635.07* 470.49*

C 247.86 n.f. 193.09 n.f.

Ca 422.67 393.37 422.67 393.37

Cd 228.80 226.50 228.80 214.44

CI 725.67* 479.45* 725.67

Co 240.73 238.89 240.73 238.89

Cr 425.43 205.55 357.87 205.55

Cs 455.53 452.67 455.53 452.67

Cu 327.40 213.60 324.75 224.70

F 685.60* n.f. 685.60 n.f.

Fe 248.33 238.21 302.05 259.94

Ga 417.21 209.13 294.36 209.13

Hg 253.65 194.23 253.65 194.23

206.24 516.12* 206.24

In 451.13 230.69 325.61 230.69

K 766.49 n.f. 766.49 n.f.Li 670.78 n.f. 670.78 n.f.

Mg 285.21 279.55 285.21 279.55

Mn 403.08 257.61 279.48 257.61

1\10 379.83 ,,){V'l (\') 379.83 202.03L.VL,.V:J

Na 589.00 n.f. 589.00 288.11

Ni 232.00 231.60 232.00 221.65

310 K. Jankowski

Table 1 (continued)

Os 375.25 228.24 222.80 225.59

P 213.61 n.f. 213.61 n.f.

Pb 405.78 220.35 217.00 220.35

Pd 340.46 n.f. 340.46 229.65

Pt 265.94 214.42 204.94 214.42

Re 229.45 227.53 204.91 197.31

Rh 343.49 n.f. 343.49 233.48

Ru 372.80 240.27 349.89 240.27

S 217.05* 545.39* 545.39

Sb 206.83 n.f. 206.83 n.f.

Se 196.03 n.f. 196.03 n.f.

Si 251.61 n.f. 251.61 n.f.

Sn 235.48 190.00 235.48 190.00

Sr 460.73 407.77 460.73 407.77

Te 214.28 n.f. 214.28 n.f.

Ti 365.35 334.90 363.55 334.90

TI 535.05 n.f. 276.79 190.86

V 437.92 n.f. 292.36 309.31

Zn 213.86 202.55 213.86 202.55

Zr 360.12 339.20 360.12 343.82

*data for helium plasma [89].

The lnost sensitive lines ofelements in the MIP spectra cover a broad range ofUVand VIS. However, in ICP a majority of intense emission lines is placed in the UV.Thus, lnicrowave plasma could be a modern excitation source recommended for qual-itative analysis, since in comparison with ICP spectral interferences are much lessprobable. An essentiallilnitation in the application of the MIP is that SOlne intenselines ofAI, Be, Bi, Cd, Ti and V overlap intense OH bands, especially in the 306-320nm range.

For analytical purposes low temperature plasmas (up to 10000 K) are utilized.MIP is definitely a plasma not in local thermodynamic equilibrium, and a consider-able difference between the electron temperature and that ofthe gas can occur. Condi-tions favorable for the occurrence of various chemical reactions exist in this type ofplasma. The excitation mechanisms in MIP are not yet sufficiently known. The mainrole is attributed to collisions with high energy electrons and Penning ionization in-volving argon or heliuln atolns in the metastable state.

Chelnical interferences are connected with the fact that the analyte excitation isaccolnpanied by reactions involving other components ofthe salnple. The decrease inthe calcium elnission in the presence ofphosphates [26] or alluninum [90] is a classi-cal exalnple of chemical interferences due to the forlnation ofrefractory cOlnpounds.This type ofinterferences can be eliminated in Iv1IP by the addition ofa spectral buffer[91].

Microwave induced plasT11a emission spectroT11etry 311

Alkali Inetals, usually present in environmental sainples, cause a positive Inatrixeffect, which leads to an improvement of analytical performance of MIP-AES forInanyeleinents [87]. An additional increase in einission is observed in the presence ofchlorides, owing to the formation· of volatile chlorides of the elements determined[87,92]. A very large increase in emission can be observed for someelelnents(1 OOO-fold forMn [93]) when thermal vaporization is used as the method ofsampleintroduction to MIP. Despite the occurrence of a clear matrix effect from such ele-ments as sodium,. potassium, calcilun or InagnesiuIn, the application of the Ina-trix-lnatching Inethod is sufficient for assuring good accuracy and precision of thedeterlninations in the analysis of environinental sainples.

ANALYTICAL PERFORMANCE OF THE MIP-AES

The .detection lilnit (DL) for individual elementsin the MIP-AES depend to agreat extent on the sample introduction technique applied. Table 2 summarizes DL forselected elements using solution nebulization. It is. generally assumed that in atoinicelnission the best detection liInits are achieved for ICP, as MIP and DCP offer smallersensitivity, whereas FAAS is in many cases the least sensitive method.

The DL for 31 elements by the MIP-AES have been determined [86]. A greatersensitivity ofthe MIP-AES in cOlnparison to that for ICP-AES was found for Ag, Cd,K, Li, Na, P, Pb and Sb. The detection limits for AI, Be, Se, As,Cu, Fe, Zn and Bi inMIP and ICP are comparable, and for the others Inuchbetter perforinance is providedby ICP. This concerns especially the determination ofmetals forining in plasma stableoxides, e.g. W, Mo, .Zr andTi.

Table 2. Comparison of detection limits by various spectroscopic techniques with solution nebulization;MIP - argon microwave induced plasma [12,13], CMP -argon capacitively coupled microwaveplasma [12,13], Iep - argon inductively coupled plasma [88],.DCP - argon direct current plasn1a[94,95], MINDAP -lnicrowave induced nitrogen discharge plasma [15], FAAS - flame aton1icabsorption spectron1etry [96].

ElementDetection limit, ng mr l

MIP CMP ICP DCP MINDAP FAAS

Ag 3 470 7 2

Al 24 500 23 15 13 20

As 30 53 150

B 10 4.8 10 6000

Ba 16 500 1,3 15 10

Ca 0.7 2 0.2 0.5 1.2 1

Cd 0.12 6 2.5 1.7 2

Cr 10 9 6 1 3Cu 9 10 5.4 1

Fe 8 150 4.6 5 280 10

312 K. Jankowski

Table 2 (continued)

K 2 40 10 5.4 1

Mg 0.6 2 0.15 0.1 13 0.1

Mn 6 8 1.4 2 2

Na 1 1 29 0.29 0.2

Ni 35 20 10 1 5.3 2

P 90 76 100

Pb 10 10 42 13 84 10

Ti 6 4 3.8 90

V

Zn

20

10

50

200

5

1.8 4

47

120

20

1

MIP-AES with the electrothermal vaporization is a useful and sensitive Inethodfor the analysis ofinicro-sainpies. The fact that the sample reaches the piasina zone asa vapour, and even partially atomized, which reinarkably facilitates its excitation, isan essential advantage ofthis Inethod ofsample introduction. In Table 3 are presentedthe DL for SOlne elementsachieved under various measurement conditions and usingvarious techniques of electrothermal vaporization including graphite rod, graphitefurnace and heated graphite atomizer, and reviewed by Carey and Caruso [23].

Table 3. Comparison of absolute detection limits by various spectroscopic techniques with electrothenllalvaporization [23,96] (in pg).

Elelllent ETV-MIP-AES ETV-ICP-AES GF-AAS

Al - 0.5 .. 400 1

As 120-300000 60-2000 8

Ca 3850 1-600 1

Cd 0.2 1-600 0.1

Cu 30-900 1.5-500 0.5

Fe 500-11000 10-100 1

Hg 6-100 4-200 5-90

Ni 110-3800 27-485 5

P 660-5000 100-2000 -

Pb 120 4-650 0.7

Se 140-250 - 20-60

Zn 400-500 0.6-800 0.1

In the cOlnbination of the hydride generation technique (HG) with MIP a lilnitedainount of the sainple Inaterial is introduced into the piasina in the gas forin. More-over, the use of relatively sinallplasma gas flow causes sinall dilution of the sampleand prolongs the tilne ofits residence in the piasina zone. The exceptionally low back-ground level is an additional advantage. As shown in Table 4 cOlnparable detectionlimits for As, Ge, Sb, Se, and Sn are obtained with various spectroscopic techniquesbased on MIP or ICP. Fricke et at. [97] deterinined nanograin alnounts ofelelnents ap-plying hydride generation, cold trap preconcentration and gas chroinatography.

Microwave induced plasnla enu'ssion spectronletry 313

Bulska et 'al. [69]ilnproved· the analytical performance of HG-MIP. by on-linepreconcentration of As, Sb and Se hydrides by hot graphite furnace trapping (GFT)and subsequent evaporization oftheanalyteinto the helium plaslna.

Table 4. COlnparison of detection limits (ng mr l ) by various atomic emission spectrometry systen1sutilized MIP or ICP with hydride generation [22,69,97].

Element HG-MIP HG-ICP HG~GFT-MIP HG-GC-MIP HG-GC-ICP

1

0.8

()QV.V0.35

0.15

0.5

1.25

2

0.12

0.14

0.031.4

Se

Sn

As 0.3 0.06 0.08

Ge 0.04 0.06

Sb 6.1 0.18

Coupling of MIP-AES with .gas chromatography is a unique. hyphenated tech-nique with a possibility of simultaneous multielement detection of the cOlnpoundsseparated [8-11,52,98]. The Inicrowave plaslna detector (MPD) belongs to the Inostsensitive detectors now used in gas chromatography. ·Especially heliulnplaslna ischaracterized by great sensitivity, both with respect tOlnetals and non-lnetals.Asshown in Table 5, for many elements the DL do not exceed several pg S-l. TheGC-MPD could be used for the identification ofall organic cOlnpounds present in thesalnple on the basis of the carbon concentration Ineasurelnent and individual reten-tion times, identification of selected classes of cOlnpounds, e.g. halogen derivativeson the basis of the heteroatomelnission measurement, speciation studies ofdifferentcOlnpounds of one element or determination of the chemicalcolnpositionof com-pounds on the basis of deterlnination of the elelnent ratio of several basic elelnents[99,100].

Table S.Analytical perforn1ance of the microwave plasma detector MPD (He-MIP-AES), [11,52].

ElementDetection limit,

Selectivity ElementDetection limit,

Selectivitypg S-I pg S-1

C 0.2 1 F 8.5 3500

H 2.2 6000 CI 16 2400

0 75 25000 Br 10 1400

N 7.0 6000 I 21 5000

P 1.5 25000 Fe 0.3 280000

S 1.7 150000 I-Ig 0.6 77000

As 6.5 47000 Pb 0.17 25000

Se 5.3 10900 Sn 1.6 36000

Si 9.3 1600 V 4.0 --

314 K. Jankowski

For the GC-MIP and other techniques ofgaseous salnple introduction a linear an-alytical graph extends to four or five orders of lnagnitude. However,. for MIP-AESwith solution nebulization this range is narrower due to full load of plasma. Ng andShen [101] achieved a linear dynamic range for several elelnents deterinined in syn-thetic ocean water in the range from 0.01 to 100 lng 1-1. Silnilar results were achievedfor several elements analyzed in fresh water [86]. Some elelnents (Au, Ca, Cd, Cu,Zn) yield instrumental responses linear over two orders of magnitude due to self-absorption effects [65,86].

In order to deterll1ine the accuracy of the ~v1IP-AESmethod, the analysis ofcerti-fied reference lnaterials was carried out, especially of vegetable and anilnal origin[29,30,34,102], and also using synthetic salnples corresponding to natural salnples[65,86]. In general, the results obtained were in good agreelnent with the certifiedvalues. However, lnatrix effects were observed in SOlne cases and additional analyti-cal procedures were applied, including addition of chelnical modifier [29] or separa-tion of the analytes [102].

In reviews concerning plasma emission spectrometry a comment could be foundthat MIP is characterized by poor precision oflneasurement owing to the lilnited sta-bility of the microwave discharge [94]. However, during the recent years technicalilnprovelnents brought an increase in the precision of lneasurements [12,13,30] . Theshort-term precision calculated for standard solutions of several elelnents (Ag, Ca,Cd, P, Pd, Zn) was froln 0.6 to 1.1% at the analyte concentration at the lng 1-1 level andfroin 1.5 to 2.0% at l-lg 1-1 level. The long-term precision lneasured for Zn and P solu-tions was 1.8 and 3.0% respectively [103]. Good precision of measurelnents wasachieved not only for standard solutions of elelnents, but also for real salnples, e.g.river water and fresh water [86] as well as synthetic ocean water [65,101].

AI1 evaluation of the MIP-AES lnethod with respect to the lnost popular instru-lnentallnethods can be found in some reviews [30,104,105].

AIR ANALYSIS BY MIP-AES

MIP is a promising excitation source for Inonitoring air and exhaust gas, even dueto the possibility of obtaining air Inicrowave piasina. Sielnens et al. [38] studied theMIP-AES for the monitoring of trace amounts of lnercury in flue gases using anon-Inixed argon-nitrogen discharge. The DL was 8 J.lg In-3 ofHg in nitrogen, whichis sufficient for carrying out on-line monitoring ofmercury for environmental protec-tion. Verlnaak et at. [106] utilized air MIP for the detection of the gaseous lead in ex-haust gases. The gas sample was introduced directly to the plaslna. Denkhaus et at.[64] deterlnined lnolecular nitrogen in natural gases by direct introduction ofthe san1-pIe into the low-pressure MIP. The emitted radiation was directed to the lnonochro-Inator by fiber optics. Linear response ofnitrogen emission was obtained in the rangeof 0-14% (v/v), and theDL was 0.01 ppIn (v/v).

Microwave induced plasma elnission spectrOl1'letry 315

Another method of analyzing gaseous .products .consists in injecting a definedvolume to the plasma gas stream. Serravalo and Risby [107] studied the determina-tion of vinyl chloride concentration in air by means of He-MIP under reduced pres-sure on the basis of the chlorine emission· for the 479.45·nITI line. The DL for vinylchloride was 300 ppm.

The determination ofsulfurin the form ofhydrogen sulfide or sulfur dioxide in airwas studied by Taylor et al. [108]. They injected to plasma up to·l Oml ofthesainplestudied. Air, helium and argonplasinas were studied and the best analytical perfor-mance \vas achieved for the latter: DL 0.2 flg ofsulfur and linear response from 100 to500 ppm.

BaUlnann and HeUlnann [78] determined organobromine compounds, hydrogenbromide and tetraalkyllead in exhaust .gases. Hydrogen bromide was preliminaryconverted into 2-bromocyclohexanol. Then organobroinine compounds were ad-sorbed on Tenax GC and the lead compound on Porapak N forpreconcentration andliberated by Ineans ofthermal desorptionto the GC-MIP-AES system. The contentsofthe compounds studied in theexhaust gases was froin several to several hundred IJg m-3.

Realner et al. [109] studied the content of the total gaseous lead (TGL) and totalparticle lead (TPL) in exhaust gases, tunnel air and lab air. The sample was transferredthrough a system in which particulate lead was collected on a filter and gaseous leadon an appropriate adsorbent. The compounds deterinined were released by means ofafreeze-drying system to the GC-MIP-AES instruinent. TGLandTPL contents lnea-sured were 20-1000 and 1000-55000 ng Pb m-3, respectively.

ANALYSIS OF WATER AND WASTE-WATER

Determination of metals and metalloids

Deterinination of impurities, for which the maximum adinissible concentration(MAC) non-toxic for live organisms was established, is essential in water analysis.Special monitoril)g programs and normalized analytical procedures utilizing effi-cient instrumental methods have been elaborated in order to obtain comprehensive in-forlnation on environinent pollution over large regions [110-114].

A comprehensive evaluation of the usability of the MIP-AESmethod for themulti-element analysis ofnatural waters [86] has been carried out on the basis of theprocedure of determining 31 trace and main elements by the ICP-AES method rec-ommended by international regulations [110]. The analytical lines and correspondingdetection limits for these elements determined by the MIP-AES in water have beenproposed. Relatively low DL are achieved, especially for alkali and alkali earth met-als. The accuracy and precision of analysis of impurities in water by the MIP-AESwas evaluated on the basis of the results obtained for two reference materials: syn-thetic river water and drinking water. For the Inain elements and a majority oftrace el~

316 K. Jankowski

ements a good correlation with the certified data was achieved. Matrix effects wereobserved when determining some elements in the synthetic river water sample due tothe presence ofeasily ionizable elements and concomitant anions. For chromium andlnanganese an over two-fold increase in the DL was found in the presence of a matrix(Ca, Na, Mg, Cl) in comparison with the results obtained for standard solutions. Silni-lar improvements in the DL were obtained for Ca, Cr, Mn, Ni, Pb and Zn when analyz-ing samples of water from deep water intakes, tap water, municipal waste water andtwo extractants used for the separation of the bioavailable fraction of heavy metals-trAm CAilc f11 "\1.LI. V~~~ ""V~.l.lJ l.l. ..L,./ J'

The MIP-AES with direct nebulization of solutions shows good usability for en-vironmental water analysis. Although the detection lilnits achieved are comparable tothose obtained in ICP for only about 50% ofthe elements studied, both techniques ful-fill the requirements of the EPA program to a silnilar extent. The DL obtained by theMIP-AES method have been compared with the Contract Required Detection Limits(CRDL) from the Environmental Protection Agency (EPA) program SOW No. 788[114] and the maximum admissible concentrations (MAC) for metals and non-metalsin ground waters recomlnended by WHO. MIP fulfils the requirements of the .EPAprograIn for 12 of 21 elements (ICP 15 of 21), and considering the possibility of ap-plying the hydride generation technique this number will rise to 17. From the compar-ison ofthe DL by the MIP-AES and MAC values presented by WHO it appears that 7elements of 15 can be determined with the lnethod described (11 when including theHG-MIP) without the necessity of preconcentrating the salnple components. It hasbeen proved that by lneans ofthe MIP-AES Fe, Mn, Zn, eu, Pb, Cr, Na, K, Mg and Cacan be deterlnined on the level, which in many cases is sufficient for the needs of atypical monitoring of pollutants in water.

However, the preconcentration oftrace impurities is essential in lnany cases. Kai-ser et al. [72] deterlnined nano and picogram amounts oflnercury in air, water, soiland milk applying different techniques ofpreconcentration and introduction ofthe el-elnent to plasma. Volland et al. [116] isolated less than 0.1 ng of Cu, Zn, Fe, Ni, Coand Bi frOln the solution during 1-2 h by lneans of hydrodynalnic electrolysis. Agraphite tube was used as the cathode. The ETV-MIP-AES system based on this tubewas constructed and multi-element analysis was perforlned. DLs below 0.01 ppbwere obtained.

The content of some lnetals and lnetalloids in water can be determined by firstconverting theln into a volatile complex. Tahni and Norvell [117] applied theGC-MIP-AES for the determination ofarsenic and antimony in drinking and seawa-ter as well as orchard leaves. The elements were precipitated with thionalid, and thenconverted into triphenyl arsine and stibine treating with phenyhnagnesium bromide.The compounds fOflned were extracted with ether and separated on a chromato-graphic column. The absolute detection limits were 20 pg for As and 50 pg for Sb,which corresponded to 50 and 125 ng 1-1, respectively to their initial concentrationsin water. The As and Sb content in the samples studied was 0.0016-11 ppm and0.00042-3.2 ppm, respectively.

Microwave induced plas11'za emission spectro11'zetry 317

Skogerboe et at. [74] used an ETV-MIP-AES setupin which the determined ele-ments were preliminary converted into volatile chloride. The absolute detection lilll-its for Bi, Cd, Ge, Mo, Pb, Sn and Zn were between 1 and.5 ng, and 0.1 ng for Tl. Themethod was applied for the determination of cadmium and lead in the 1-2 ng Illl-lrange·in water samples.

Lunzer et at. [118] used a continuous HG-MIP-AES system for thedeterillina-tion ofarsenic, antilnonyand selenium. The detection limits for As, Sb and Se were0.7,0.9 and 0.4 ng ml- I , respectively, and the precision ofdetermination was 3-4 %(RSD). The matrix effects occurring when determining As in seawater were also stud-ied.Bulskaet at. [119] determined below 0.1 mg 1-1 ofarsenic and selenium in waterby preconcentration of the separated hydrides in a graphite· furnace filled with spe-cially prepared vitreous carbon and then introducing thereleased compounds to MIP.Earlier Lichte and Skogerboe [120] determined 0.02-1.32 ppm As in water by theHG-MIP-AES method.

Dietz et at. [121] determined arsenic, selenium, antimony by HG-MIP-AES andIllercury by (cold vapour) CV-MIP-AES in river and waste waters. The content oftheeleinents mentioned varied in the 3-150-J.lg 1-1 range and respective DLs froill 2 to .13J.lg 1-]. Noijri et at. [73] determined below 1 ng 1-1 of mercury in lake water byCV-MIP-AES. The mercury vapour was preconcentrated by collection on gold de-posited on a porous structure and then therillally released to the plasma.

Tao et at. [122] deterinined berylliulll in lake water on a ng 1-] level byGC-MIP-AES. Berylliulll was preconcentrated by extraction as acetylacetonate.The DL for Be was 0.33pg ml-1 ofwater sample. A similar procedure was applied byTahni and Andren [123] when analyzing selenium in different sainples originatingfroIn the combustion ofcoal at steaInplant. Aftersainple digestion,selenium was ex-tracted as a volatile complex (p-nitro-piaselenol). The Se content in the analyzed ma-terials was from 0.05 to 10 J.lgg-I.

Madrid et at. [61] studied the FIA-MPT-AES system to deterininecopper in sea-water. Sodiuln diethyldithiocarbamate as the chelating agent and ·reversed-phasechroinatography microcolumn were used for separation and preconcentration ofcop-per. The detection limit for Cu was 0.16 ng 1-1.

Determination of non-metals

The determination of chloride, bromide, iodide [124], fluoride [125J as well ascarbon, phosphorus and sulfur [126] in aqueous solutions on the mg I-I level shouldbe mentioned among the analytically important applications ofhelium MIP. Barnett[77], and also Camuna et at. [127] determined Cl, Br and lin water continuously gen-erating halogens and·hydrohalides, which were introduced to MIP after separationfrom the aqueous phase. TheDL did not exceed 0.5 mg 1-1.

Chiba et at. [128] determined fluoride in natural waters by GC-MIP-AES afterextraction with toluene in the presence of trimethylchlorosilane as the derivatizingagent. TheDLof7.5pgs-1forFwasachieved.l.3 J.lgmr~l ofFinseawateralldO.l J.lg

318 K. Jankowski

ml-1 in tap and pond water samples were determined. Haraguchi [129] reported theDL of20 J.lg ml-1 for a similar analysis of natural water.

Nakahara et al. [130] elaborated two analytical procedures for the determinationof iodide in waters. The indirect method utilizes the decrease ofinercury emission in-tensity in the presence of iodide in highly acidic medium. In continuous flowCV-MIP-AES systein the DL for iodine was 50 ng ml-1• The direct method permitsthe determination of the iodide and iodate content in seawater and brine after conver-sion into iodine [131,132]. The DL was 2.3 ng ml-1 of iodine.

.AJvarado and Carnahan [133] determined some organic compounds ofsulfur, ase.g. cysteine and menthionine, by converting them into hydrogen sulfide, pre-concentration in a liquid nitrogen trap and excitation in a He-MIP. Thus, they coulddetermine these compounds in water on a J.lg 1-1 level. The DL for sulfur was 0.4 ppb.A similar procedure was accepted by Nakahara et al. [79] when determining below 1mg 1-1 ofsulfide in wastewater. However, when determining the content ofsulfites inwine at the 100 J.lg ml-1 level they liberated them from the sample as S02. The detec-tion lilnit was 0.13 ng ml-1 for sulfur generated as hydrogen sulfide and 1.28 ng ml-1

as sulfur dioxide.Gebersmann et al. [134] separated volatile organic sulfides and thiols by means

of purge-and-trap technique before deterinining their content in lake water and sea-water as well as in four types ofbeer and coffee by the GC-MIP-AES. Dimethyl sul-fide, carbon disulfide and etanothiol were at the 3.5-50 ng 1-1 level calculated withrespect to sulfur.

Mitchell at al. [135] applied the ETV-MIP-AES method for determining in waterthe total organic carbon (TOC) and particulate organic carbon (POC) at the lIng 1-1 level.The sample was placed in a platinum boat, water was evaporated off and by applyingan appropriate oxidizer and temperature program the particular compounds deter-Inined were released.

GC-MIP-AES was applied for the analysis of water polluted with halogen or-ganic compounds ofvarious classes [99,100]. Chibaand Haraguchi [136] determinedtrihalomethanes in tap, river, sea and pond waters at the 0.02-55 ng 1-1 level. Thecharacteristics of the MPD for F, Cl, Br and I was as follows: detection limits 36, 32,28 and 6.7 pg S-1 and selectivity 820,1000,530 and 530, respectively. Quhnby et al.[137] determined below 1 J.lg 1-1 of trihalomethanes in drinking water by thepurge-and-trap technique. By means of the purge-and-trap injection device Slaets etal. [138] determined volatile haloganated organic compounds (VOC) containing CI,Br or I in seawater at 0.05-15.28 J.lg 1-1 concentrations.

Turnes et al. [139] determined below 1 J.lg 1-1 ofchlorophenols in drinking waterapplying the solid phase extraction (SPE) for separation and preconcentration of theelements determined. The analytical conditions of determining halogen derivativesofhumic and fulvic acids in tap water were investigated by Quimby et al. [140]. Thepossibilities of separating and determining dioxins [141] and poly(chlorinated bi-phenyls) [142] by means of GC-MIP-AES were also studied.

Microwave inducedplasma emission spectroTnetry 319

Much attention is drawn toward the determination ofadsorbable halogen organiccompounds (AOC). Koschuh et al. [143] separated AOe 'scontaining Cl and Br frominorganic chloride, concentrated on activated carbon, and then subjected to pyrolysisand the released compounds were absorbed by 0.1 mol 1-1 sodium hydroxide. Afteroxidation to chlorine and bromine they introduced the resultant to helium MIP.TheDL for Cl and Brwere 3 and 8 ng ml-] , respectively. Lehnert et al. [144] elaborated aspecial measuring system for the determination ofAOC's utilizing preconcentrationon activated charcoal and thermal desorption. The absolute detection limit for .chlo-rine was 0.2 IJg.

ANALYSIS OF SOILS, SEDIMENTS AND BIOLOGICAL MATERIALS

The analysis ofcomplex materials such as soils or sediments is a valuable sourceof information on the analytical performance of a method. Although the nUlnber ofpublications concerning the application of MIP-AES for the determination of totalcontent ofelemental pollutants in this type ofmaterials are not too numerous, it is re-markably supplemented by speciation studies described in the next section.

Seeley at al. [145] performed simultaneous multielement detection of7 elementsin sediments and coal by pyrolysis-gas chromatography. Absolute detection lilnitsobtained withthe MPD for Se, S, P, 0, N, As and C were 4, 10, 17, 300, 20, 3 and 0.2pg,. respectively..Whenapplying the continuous HG-MIP-AES method, Ng et al.[146] determined selenium in soil. The DL was 40 ng ml-1 Se.

Jin et al. [147] determined Ag, AU,Ge, Pb, Sn and Te in sediments by means ofETV-MIP-AES. The sample was digested with simultaneous removal ofsilica. Thesolution obtained was vaporized from a tantalum filament loop. The DL was from 3 to147 pg. Ag, Sn and Te were determined at the level of 0.1-5 J.lg g-l in sediments withcertified values for the elements. Kawaguchi and Vallee [93] determined picogralnsofzinc by vaporizing lnicrogram amounts ofenzyme samples into a He-MIP. Barnett[148] determined nickel and lead in animal bones·(reference material). The sampleswere digested with sulfuric and nitric acids, and vaporized from a tantalum ribbon.

The applicability ofthe GF-MIP-AES method in the analysis ofbiological mate-rials for the content ofheavy metals has been shown. Leis and Broekaert [34] as wellas Aziz etal. [149] determined below O.lllg g-l ofCu, Fe, Mn, Pb andZnin samplesofspinach, orchard leaves and bovine liver afteracid digestion. In an other procedurethe powdered 2 mgsampleswere placed directly in a furnace, the organic matrix wasremoved at lower temperature, and then the elements determined were released andintroduced to argon MIP.

Yang et al. [29] determined heavy metals in tea leafs and hUlnan hairatthe J.lg 1-1level. The samples were digested in acids, and then placed in a graphite furnace, add-ing palladium as the chemical modifier. The atomized sample was introduced into aAr-MIP (TE Iol resonator). When applying the standard addition method a satisfac~

320 K. Jankowski

tory accuracy ofdeterminations was achieved for Ag, CU,Fe, Mn and Pb. Heltai et al.[102] determined Fe, Cu and Zn in tomato and orchard leaves and bovine liver. Mod-ified cellulose was added to the digested samples and the elements determined wereseparated as thiocarbamate complexes. Then, the elements were eluted by means ofnitric acid and froln 5 to 50 J.lI of the solution obtained was introduced to.a graphitefurnace coupled with a toroidal Ar-MIP.

Microwave plasma is readily utilized in environmental analysis when coupledwith the hydride generation technique. Schickling et al. [150] separated arsenic asi\sH3, concentrated with trapping in a graphite furnace coated with platinuln, andthen thermally vaporized and introduced to argon or helium MIP. From 0.05 to 10 J.lgg-l As were determined in citrus leaves, human hair, mussel tissue and pig kidney.Nakahara and Takeuchi [151] applied HG-MIP-AES with nitrogen plasma in theanalysis of arsenic in seaweed and scallop. For this experimental setup a DL of 3.13ng ml-1 and linear response of 10-5000 ng mg-1 were achieved.

De la Calle-Guntinas et al. [152] determined selenium present in wheat asselenolnethionine by means ofthe GC-MIP-AES after derivatization. The analyticalperformance ofFPD, MS and MIP-AES detectors has been compared in this study.Absolute detection limits for selenium were 0.9,0.015 and 0.78 ng, respectively.

The application ofcoupled techniques increases the possibilities ofutilizing MIPin the analysis of cOlnplex lnaterials ofnatural origin. Riviere et al. [153] studied thepossibility of applying a surfatron for pesticide analysis by the CGC-MIP-AESmethod. Earlier Bache and Lisk [32] determined picogram alnounts ofpesticides con-taining sulfur, halogens or phosphorus in food products such as wheat, potatoes, on-ions, carrots, cabbage, sugar beet, powdered lnilk and chicken meat as well asherbicides containing iodine in soil, wheat and oats samples [154]. The analysis ofpesticide content in food was dealt with also by Wylie and Oguchi [155].

APPLICATION OF MIP-AES TO SPECIATION STUDIES

In recent years considerable progress occurred in the speciation studies ofheavy~

metals and metalloids [11,21,156,157]. The appearance ofplasma excitation sourcesand their application for multielelnent analysis by lneans of atomic emission spec-trometry and mass spectrometry at the ultra-trace level were one of the reasons per-mitting the broadening of these studies. These lnethods in their essence perlnit,however, the determination of only the total content of elements in the sample stud-ied, but coupling with chrolnatographic techniques afforded a very efficient tool forspeciation studies. Due to the selectivity of the Atomic Emission Detector (AED),very clear chromatograms are obtained even in the analysis of cOlnplex environmen-tal samples. The elnission measurement at a wavelength corresponding to the lnetalstudied causes that the detector records only one, the required class of organic com-pounds.

Microwave induced plasma emission spectrometry 321

A large number ofpapers is concernedwiththe speciation ofalkyltin compounds[158-162]. Liu et al. [33] elaborated the conditions of extractive separation andspeciation analysis for 15 different alkyltin compounds which can occur in soil andsediments. Rodriguez-Pereiro et al. [163] applied multi-capillary GC-MIP-AES forspeciation studies ofalkyllead, alkylmercury and alkytin compounds in different en-vironmental samples. The accuracy of the Inethod was confirmed by carrying out theanalysis of tin compounds in certified materials: sediment and fish tissue.Szpunar-Lobinskaetat. [164] studied the speciationof tin compounds inwater anddetermined 1O~140 ng I-I oftin as 111onobutyltin, 8-67 ng I-I as dibutyltin and 4-11 ng 1-]as tributyltin. The cOlnpoundswere preconcentrated·on aSPE column and on-linederivatizatizedby means oftetraethylborate prior to introduction on the capillary col-umn.

Liu etal. [165] determined simultaneously organic tin, lead and mercury COln-pounds in environmental salnples using capillary gas· chromatographyCGC-MIP-AES.The calibration curves exhibited lineritybetween 2.5-2500 ng Inl-1

forSn andPb,and 2.5-10000 ng ml-I for Hg.Mercury is the secondlnetal often met in speciation studies [166,167]. Snell et at.

[168] studied speciation of mercury in the natural gas condensate using on-linepre-concentration by means ofcold vapor generation or solid-phasernicro-extraction(SPME) and· GC-MIP-:-AES. The DL fordimethylmercury was 0.24~g I-I and formethyhnercuryandHg(II) 0.56 J.lg I-I.

Donaiset al. [169J applied the GC-MIP-AES method for speciation studies oflnercury in various certified materials ofsea origin. The samples ofsediments, crusta-ceansand fishtissues were first subjected to solid-liquid extraction system. The lner-cury·compounds in the aqueous phase were extracted with toluene, and finally thetoluene extract was purified from high molecular lnass compounds by means of gelchrolnatography. The methylmercury content in the samples studied was from 0.6 ng r-- Ito 13 J.lg g-I ofHg, and the total mercury content was from 0.04 to 28 J.lg I-I. The DLfor mercury was O.lpg S-I.

When •studying the methylmercury content in fish tissue, Palmeri and Leonel[17OJ applied a ml;llti-step procedure ofpreparing the sample covering alkaline diges-tion, extraction and derivatization·· with· sodium tetraphenylborate prior toGC-MIP-AES determination. The DL ofMeHg was 0.1 J.lg g-I. The accuracy ofde-termination was checked by means. of BCR CRM 464 (tuna fish) and NRCCDORM-2 (dogfish lnuscle).certified reference lnaterials.

Elnteborg etal.. [171] studied the speciation of mercury in sediments by super-critical fluid extraction and GC-MIP-AES. They determined from 8 to 40 ng g--I oflnethylmercury, while the content of inorganic mercury in the samples was from 500to 2000 times higher. The same group determined mercury compounds in natural wa-ters, rich in humic acids [172]. Mercury was concentrated by solid phase extractionon a column packed with a resin \vith DDTC groups, followed by elution andderivatization of the cOlnpounds. The content ofMeHg+ was 0.2__0.3 ng I-I, and that

,

322 K. Jankowski

of inorganic mercury 2-5 ng 1-1. Chiba et al. [173] studied the. speciation ofHg com-pounds in seawater by means of GC-MIP-AES achieving DL below 0.5 J.lg 1-1.

Mena et al. [174] applied the FIA-GC-MIP-AES system equipped with micro-coluinn for preconcentration to deterinine Hg in canal water. The content of organicmercury in different samples varied from 40 to 160 ng 1-1 , and that of inorganic mer-cury froin 100 to 340 ng 1-1. Costa-Fernandez et al. [175] studied the speciation ofHgand As in seawater, tap water and urine using a flow system. The determined com-pounds were separated by high permeation liquid chromatography, and then con-verted to volatile compounds. By the HPLC-HG-:L\1IP-i\ES Inethod the DL for fOUforganoarsenic cOlnpounds were from 1 to 6 ng ml- J, and by theHPLC-CV-MIP-AES Inethod 0.15 ng Inl-1 in the inorganic forin and 0.35 ng ml-1 ofmethylmercury (calculated with respect to Hg) could be detected.

Lead is the third leading eleinent in speciation studies [163,176], the alkyl com-pounds ofwhich are determined first of all in places liable to the elnission ofvehicleexhaust gases. Reamer et al. [109] determined 5 lead compounds in air and exhaustgases. A sample of gas was transferred through a column packed with an appropriateabsorbent. The liberated cOlnpounds were then concentrated by cold trapping and de-termined by Ineans of the GC-MIP-AES. The contents of particular alkyllead com-pounds varied from 0.5 to 650 ng m-3.

Alkyllead compounds are sought in tap and rain waters [160,177]. LobinskiandAdams [178] determined four alkyllead cOlnpounds using theirextractive separationas thiocarbainate complexes and GC-MIP-AES. The content of particular com-pounds in water studied was 0.3-1.7 ng 1-1. Wasik et al. [179] determined alkylleadcompounds in tap water applying the derivatizating reaction in situ. In the acetatebuffer medium of pH = 4 they added tetrabutylammonium tetrabutylborate and ex-tracted the derivatized alkyllead compounds with hexane. The DL for particularanalytes were in the 43-83 pg 1-1 range. In a similar way Heisterkamp and Adains[180] studied the speciation of lead in tap water and peat. The content of individualalkyllead cOlnpounds in water did not exceed 0.5 ng 1-1, and in peat 20-1500 pg gJ.The speciation studies of lead in snow from Greenland carried out by Lobinski.et al.[181] is a special case. A similar procedure has been applied as when analyzing tapwater, but as Inuch as 1250-fold preconcentration of the traces was necessary. Thelead compounds content in snow was from 0.02 to 0.48 pg g-J.

De la Calle-Guntinas et al. [182] determined selenium(IV) and selenium(VI) byIneans ofconversion ofselenium(IV) into volatile diethylselenium, concentration bycold trapping and GC-MIP-AES. Selenium(VI) was determined in river and mineralwaters at a level below 1 J.lg 1-1 preceding the reaction of diethylselenium formationby reduction to seleniuln(IV). Volatile organoselenium compounds were determinedin lake water by the purge-and-trap GC-MIP-AES. The DL for dimethyldiselenidewas 2 pg ml-1 [183].

Microwave induced plasma emission spectronletry

FINAL REMARKS

323

The MIP-AES is a usefultnethod for the trace analysis and speciation studies inenvironmental samples. When coupled with appropriate sample introduction tech-niques, such as electrothermal vaporization, hydride generation, chetnical vapourgeneration or gas chromatography, it is possible to determine a group of eletnents atthe ngg-I level.The. possibilityofdetenllining traccamounts ofnon-metals, al1dfirstof all of halogens is a characteristic feature of He-MIP-AES. The determination oftrace amounts ofalkali metals is the second attractive field ofMIP-AESapplications.Moreover, satisfactory low detection limits are achieved for tnetals of the group I band II b of the periodic system and for elements forming volatile hydrides.

The versatility·ofthismethod and. compatibility of its operating parameters withthe parameters of comtnonchromatographic techniques,flowinjection analysis Orhydride generation tcchniqueare of essentialimp()rtance for the positive evaluationof the method. GC-MIP-AES is a technique of choice for studying the speciation oforganometallic compounds in the environtnent.

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ReceivedJuly 2000Accepted February 2001