Anal. Chem. 1992, 64 442 R-487 R I
(N74) Loveli, P. A.; Shah, T. H.; Heatley, F. Polym. Commun. 1991, 32, 98-103. (N75) Heffner, G. W.; Pearson, D. S. M e c m b c u b s 1991, 2 4 , 6295-9. (N76) Podzimek, S.; Eichler, J.; Tkaczyk, M. J . C h r m t c g r . 1991, 547, 195-201. (N77) Mlkolajczyk, L.; Haeusler, K. 0.; Wetzel, H. Acta Polym. 1990, 47, 593-4 (in German); Chem. Abstr. 1991, 774, 44152~. (N78) Podzimek, S.; Dobas. I.; Svestka, S.; Tkaczyk, M.; Kubin, M.; Sterba, V. J . Appl. P w m . Sci. 1991, 42, 795-800. (N79) Taenzer. W.; Szesztay, M.; Laszlo-Hedvig. 2.; Fedtke, M.; Tudos, F. Angew. M e k r o d . Chem. 1990, 774, 81-8. (N80) Lehtinen. A.; Jakosuo, H. Polym. Meter. Sci. Eng. 1991, 65, 93-4. (N81) Itsikson, L. B.; Tsvetkov, 0. N.; Kolesova, 0.E. Nefiekblmlya 1991, 3 1 , 684-7 (in Russian); chem. Abstr. 1991, 175, 2832421. (N82) Sadku, E. R.; Peacock, N. Angew. Mekromol. Chem. 1990. 787, 67-74. (N83) Barteis, H.; Hailensleben, M. L.; Pampus, G.; Schdz, G. Angew. Mekr o d . Chem. 1990, 780, 73-84. (N84) Wu. C. S.; Senak. L.; Curry, J. F. Polym. Meter. Sci. Eng. 1901, 6 5 , 85-8. (N85) Huang, S. H.; Radosz, M. Fluid phase Equlllb. 1991, 66, 23-40. (N86) Jiang, Y.; Liang, E.; Wang, Y. Sepu 1990, 8 , 194-5 (in Chinese); Chem. Abstr. 1990, 772, 2078521. (N87) Jennings, P. W.; Pribanic, J. A. S. Fuel Sci. Technol. Int. 1989, 7 , 1269-87. (N88) McCaffrey, G. Repr.-Am. Chem. Soc., Dlv. Pet. Chem., 1990, 35 (3), 389-95. (N89) Woods, J. R.; Kotlyar, L. S.; Montgomery, D. S.; Sparks, B. D.; Rlpmeester. J. A. F w l S c i . Technol. Int. 1990, 8, 149-71. (N90) Mdiner, R.; Ibarra, J. V.; Lagarma, M. D. Fuel 1989. 6 8 , 1487-8. (N9l) Cerny, J.; Machovic, V. Chem. Rum. 1990, 40, 97-101 (in Czech); Chem. Abstr. 1990, 772, 1593756. (N92) Delgado, G. A.; Gottneid, D. J.; Ammeraai, R. N. ACS Symp. Ser. 1991, 458 (Blotechnoi. Amylodextrin Oligosaccharides), 205-1 1. (N93) Jackson, D. S.; Gomez, M. H.; Waniska, R. D.; Rooney, L. W. Cereal Chem. 1990, 67, 529-32. (N94) SuorMi, T.; Pessa, E. J . Chromatcgr. 1991, 536. 251-4. (N95) Endo, S.; okeda. K.; Nagao, S. J . Jpn. Soc. Food Sci. Technol. 1991, 38, 7-15 (in Japanese); Biosis 1991, 9 7 , 203241. (N96) Miller, D.; Senior, D.; SutcHffe, R. J . WoodChem. Techno/. 1991, 1 7 , 23-32. (N97) Kim, S. S. Dlss. Abstr. Int. 6 1990, 5 7 , 1058. (N98) Galletti. 0.C.; Chiavari, G. J . Chromatogr. 1991, 536, 303-8. (N99) Ni, E.; Yu, A.; Lin. M.; Zhu. 2.; Chang, F. Fenxi Cesbl Tongbao 1990. 9 (3), 17-21 (in Chinese); Chem. Abstr. 1991. 714, 124747r. (N100) Liindner, A.; Wegener, G. J . Wood Chem. Technol. 1990, 70. 331-50. (N101) Soltes, L.; Lutonska, H.; Sandula, J.; Milovicova, D. J . App/. Polym. Sci. Appl. polym. Symp. 1991, 48 (Polym. Anal. Charact. 3), 33-8. (N102) b a t h o v a , M.; %Res, L.; Mislovlcova. D.; Zuboc, V.; Fugedi, A. J . ChrOmtogr. 1990, 509, 213-8. (N103) Horvathova, M.; Mislovicova, D.; Soltes, L.; Tuzar, 2 . ; Gemeiner, P.; Zubor, V. Carbohydr. P w m . 1991, 15, 79-88. (N104) Chabrecek, P.; Soltes, L.; Orvisky. E. J . Appl. Polym. Sci.: Appi. Poly” Symp. 1901, 48 (Polym. Anal. Charact. 3). 233-41. (N105) Chabrecek, P.; Soltes, L.; Kailay, 2.; Novak, I.ChromatcgraphLa 1990. 3 0 , 201-4. (N106) Massbt, P.; Baron, A.; Farhasmane, L.; Parfait, A. Sci. Allments 1991. 7 7 , 477-89 (in French); Chem. Abstr. 1991, 775, 2548954. (N107) Endress, H.-U.; Omran, H.; Gierschner, K. Lebensm.-Wiss, Technol. 1991, 2 4 , 76-9. (N108) Dickenson, J. M.; Moms. H. G.; Nieduszynaski, I . A.; Huckerby. T. N. Anal. Biochem. 1990, 190, 271-5. (N109) Thurl, S.; Offermanns, J.; Mueller-Werner. B.; Sawatzki, G. J . ChroM t o g r . 1991, 568, 291-300.
(NilO) Henry, B. T.; cheema. M. S.; Davis, S. S. Int. J . phann. (Amst.) 1991. 73. 61-8. (N111) Berden, M.; Berggren, D. J . W l S c l . 1990, 47, 61-72. (N112) Finger, W.; Post, B.; Klamberg, H. 2 . ptlenzenerneehr Bodenkd. 1991. 754. 287-92 (in German). B&s& 1991. 91. 484917. (N113) ’&, A. d.; Park, J.‘S.; Sharp, B.’L. Ana/yst (London) 1990, 775, 1429-33. ( N 1 W Bowmart, M.; Rlchou, M.; Fevrier, G.;Benaim, J. Envkon, Technd. 1990. 7 7 . 145-50. (N115) Hlgeehl, K.; Kawahara, A.; Wekida, S.; Yamane, M.; Takasuka, S. Bun&/ Kamku 1990. 3 9 , 383-5 (in Japanese); Chem. Abstr. 1990, 173 84523k. (N116) Nojki, K.; Harlgal, S.; Mas&. T. Ymul to Helsul 1990. 3 2 , 219-23 (in Japanese); Chem. Abstr. 1990. 772, 2043471. (N117) R a w . R.; Maudari, E.; Calemma. V. J . Chfomatogr. 1991, 547. 419-30. (N118) Paoiini, J.; ChMy. W. Scl. TotalEnvkon. 1990, 97, 107-14. Swlft. R. S. SdlBid. 6 b c h m . 1990, (Nll9) Keer, J. I.; McLaren, R. 0.; 22. 97-104. (N120) &&IS, R. A,; Warren, F. V.; Bidiingmeyer, B. A. J . Llq. chrometogr. 1991. 74. 327-36. (N121) bawicins, J. V.; Forrest, M. J.; Shepherd, M. J. J . Llq. Chromtogr. 1990, 73, 3001-11. (N122) Trugo, L. C.; De Marla, C. A. B.; Werneck, C. C. FoodChem. 1991, 42, 81-8. (N123) Heuslnger, H. Carbohydf. Res. 1991, 209, 109-18. (N124) Herbemold. M.; Bendel, H. D.; Nuyken, 0.; Poehlmann, T. J . nomet. Cbem. 1991, 473,65-78 (in German); Chem. Abstr. 1991. 775, 2324431. (N125) Changui, C.; Stone, W. E. E.; Vielvoye, L. Analyst (London) 1990, 715. 1177-80. (N126)‘ Takata-E.; Shirai, K.; Okada, Y. Chem. Ewp. 1990, 5 , 929-32. (N127) Cam, D.; Alblzzatl, E.; Clnquina, P. Makromol. Chem. 1990, 797. 1641-7. (N128) Kalyamin, A. V.; Moskvin, L. N. Z b . Anal. Khlm. 1990, 45, 213-21 (in Russian); Chem. Abstr. 1990, 772, 228713b. (N129) Daft, J.; Hopper, M.; Hensley, D.; Slsk, R. J . Assoc. Off. Anal. Chem. 1990, 73. 992-4. (N130) Schwedt, 0. LaborPTexs 1990, 74, 804, 606 (in German); Chem. Abstr. 1990, 173. 223838g. (N131) Ishli. Y.; Adachi. N.; Taniuchl, J.4.; Sakamoto, T. J . Pes&. Scl. 1990, 15, 225-30 (In Japanese); 6iosis 1990, 90, 335056. (N132) Chamberlain, S. J. Analyst (London) 1990, 775, 1161-5. (N133) Hale, R. C.; Bush, E.; Gallagher, K.; Gundersen. J. L.; Mothersheed, R. F. J . C h m t o g r . 1991, 539, 149-56. (N134) Czuczwa. J. M.; AltorcLStevens, A. J . Assoc. Off. Anal. Chem. 1989, 72, 752-9. (N135) Winkelmann, W. Lebensmlttelchem ., Lebensmlttelquel. 1990, 17 (Spielwaren Scherzartikel), 47-51 (in German); Chem. Abstr. 1991, 7 74, 84102. (N136) Ono, S. Jpn. Pat. 2259463, Oct 20, 1990; Chem. Abstr. 1981, 174, 843452. (N137) Krusche, G.; Illert, J.; Mandery, H. CbrmtcgrapbLa 1991, 3 7 , 17-20. (N138) Sarrade, S.; Rim, 0. M.; Autret, J. M.; Takerkart, 0. Lebensm.-WLss. Techno/ 1991,24, 23-8 (in French); C l ” . Abstr. 1991, 775, 113012s. (N139) Ohya, H.; Halo, A.; Negishi, Y.; Matsumoto, K. Meku 1990, 15, 62-71 (in Japanese); Chem. Abstr. 1990, 773, 153612~. (N140) Kolegov, V. I.; Kharltonova, N. E.; Marinin. V. 0.; Shevchuk, L. M.; Kiseleva, N. V.; Nlkolaeva, T. V. Vysokomol. W i n . , Ser. A 1990. 3 2 , 2458-81 (in Russian) Chem. Abstr. 1991, 775, 10107~. (N141) M r , R.; Soponkanaporn, T. J . Envlron. Eng. (N.Y.) 1990, 178. 343-60.
em-
Plasma Emission Spectrometryt Diane Beauchemin,* J. C.Yves Le Blanc, Gregory R.Peters, and J a n e M.Craig Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6 A. INTRODUCTION
The principal author (as can be seen from her bio a hical note) is working in the area of inductively couplerpyasma maw spectrometry (ICP-MS) and is not currently focusing on the field of plasma emission spectrometry (although it is
* Author to whom correspondence should be addressed. ‘This review is dedicated to the memory of Dr.Peter Neil Keliher who unexpectedly died of a heart attack on July 9, 1990. 442 R
‘in the works”). So, when Analytical Chemistry approached D.B. to ask her to continue the (very impressive) work of the P. N. Keliher group who wrote this review for the last 12 years (see for exam le AI), her first reaction wa: “Well, this is not really my fie18...11.Of course, a large number of developments occurring in plasma emission spectrometry are directly applicable or easily adapted to plasma source MS, and therefore, anybody seriously involved in the latter field should keep up-to-date on what is happening in the former one. So, D.B. acce ted (obviously!) this great opportunity (not to mention c d e n g e ) and convinced her graduate students to participate.
0003-2700/92/036~442~$~0.00/0 @ 1992 American Chemical Society
PLASMA EMISSION SPECTROMETRY Dlam Besuchemin is Assistant Professor of Chemistry at Queen’s University. She received a B.S. in Chemistry from the Universit6 de Montrhl and stayed on to obtain a Ph.D. in Analytical Chemistry at the end of 1984 (under the supervision of Joseph Hubert). She then worked as a Research Associate in the Chemistry Division (now the Institute for Environmental Chemistry) of the National Research Council of Canada, In collaboration with Jim. W. McLaren. She works at Queen’s since the summer of 1988 where she is actively involved in extending the capabilities of inductively coupled plasma mass spectrometry (ICP-MS), although she also has some other interests (see the biographical notes of the coauthors). She is taking several approaches, either individually or in combination. These include flow injection techniques (on-line pretreatment, on-line preconcentration, hydride generation, etc.), mixed-gas plasmas, coupling to chromatography (both gaseous and liquid), and slurry nebulization. The techniques are used for both environmental and medical applications.
J. C. Yver Le Blanc received his B.S. degree in chemistry from the Universitd de Montrhl in 1989. He is presently completing his M.S. on electrospray mass spectrometry at Queen’s University, under the joint supervision of Professor Beauchemin and Dr. K. W. Michael Siu (of the Institute for Environmental Chemistry, National Research Council of Canada), and will carry on for a Ph.D. degree. He is interested in developing sample introduction systems for both ICP and mass spectrometer instruments.
Gregory R. Peters is currently working toward his Ph.D. degree at Queen’s University under the direction of Professor Beauchemin. He received his B.S. (Honours Chemistry, Minor Nuclear Science) degree from Simon Fraser University (British Columbia, Canada) in 1989. While an undergraduate, he was employed by several governmental and industrial laboratoriesacross Canada as part of the Cooperative Education Program at SFU. He is currently involved in both ICP-MS and microwave induced plasma (MIP) spectrometry as elemental detectors for gas chromatography (GC).
Jam 1111. Crab received a B.S. degree in chemistry from Queen’s University. She is currently working toward a Ph.D. degree at Queen’s University under the supervision of Professor Beauchemin. Her project involves the development of ion mobility spectrometry (IMS) as a tool for environmental monitoring and requires the development of an interface between liquid chromatography and IMS (which cannot tolerate any water). Hence, she has grown an interest in desolvation techniques.
[Asthe reader might expect, the convincing part was the most difficult ..I The field of emission spectrometry is very wide and some limits had to be set for the scope of this review. Readers of previous reviews will have already noted that the title now includes the word “plasma” to clearly exclude flames, which are separately covered in this issue, in a review entitled “Atomic Absorption, Atomic Fluorescence and Flame Spectrometry” by Kenneth W. Jackson. FAPES (furnace atomization plasma emission spectrometry),FANES (furnace atomization nonthermal excitation spectrometry), and laser-induced plasma for excitation of atomic emission in an electrothermal atomizer, which are “hybrids” between a graphite furnace and a plasma, are also excluded from this review (they are covered by Kenneth W. Jackson). Finally, no reference will be made to papers on plasma source MS, unless they contain a comparison with emission spectrometry. For
’
a critical survey of the developments in plasma source MS, the reader is referred to the section, in this issue, entitled “Atomic Mass Spectrometry” by David W. Koppenaal. However, plasma atomic fluorescencespectrometry (AFS) is included since, after all, fluorescence is a type of emission. This review will therefore cover plasma emission/fluorescence spectrometry for the period of late 1989 to late 1991. No attempt was made to provide an all-inclusive bibliography since this is readily available from Chemical Abstracts and other abstracting services. We have made a point of not mentioning papers unless we had thoroughly read (and hopefully understood...) them. Our coverage was therefore restricted by the number of journals that we had access to (through Queen’s University and the National Research Council of Canada), as well as by answers to our requests for reprints (which was probably affected by the Canadian postal system...). In order to facilitate our job for the next review, we would be very grateful if everybody involved in the field of plasma source emission and/ or fluorescence spectrometry would be kind enough to systematically send us reprints of their work as they become available. Please do so, no matter what the language of the publication is. Our research group includes people who are fluent in English, French, and Chinese (Mandarin), and we have no problem obtaining translations for other languages (this is one advantage of working in a multicultural environment such as a university!). Nonetheless, we have tried to be as logical in our coverage as possible: we start with the beginning, i.e. sample pretreatment, and work our way from one end of a plasma emission instrument, i.e. the sample introduction system, through the plasma source and its detection system, to the other end, i.e. data processing. In each “category”,we highlight signScant (or potentially significant) developments with some examples of applications. We hope that our selective and somewhat critical coverage will be useful to the reader. As was justly pointed out by Mermet (A2) during his evaluation of the complementary and competing aspects of ICP-AES, ICP-MS, and GFAAS (graphite furnace atomic absorption spectrometry),the limitations are not so much with the techniques but with the chemistry (sample pretreatment and conservation) preceding the actual analysis. This has certainly been realized during the past 2 years, where the use of microwave digestion and the development of selective extraction and, especially, preconcentration/separation techniques has been popular for sample pretreatment. In fact, more and more people cannot do without flow injection techniques (with the versatility of these techniques,who could blame them?) to carry the sample pretreatment on-line with the plasma detector. Many researchers have put in a lot of effort to circumvent the “Achilles’ heel” of atomic spectroscopy, namely sample introduction. Both fundamental studies and the development characterization of novel introduction systems for liquid, so(id, and gaseous samples have been reported, and so, a large section of the review is devoted to them. There has also been many developments in atomization/ ionization/excitation sources over the last 2 years, which has resulted not only in new/improved sources but also in a better understanding of a t least some of the processes occurring in the plasma. For instance, computer modeling of plasmas (especially the ICP) has progressed quite a bit. Boumans (A3) published a philosophical yet realistic dissertation on the problem of a useful understanding of spectroscopic techniques in which he arrived at the conclusion that fundamental studies should be to some extent “re-digested“ and published is such a way as to facilitate applications, chemometrics, and instrumental developments. Finally, several innovative developments were made on detection systems and data processing, in particular with respect to line selection. Several things became apparent during this review, which we find quite alarming. Many papers do not make appropriate reference to earlier work in their area. Neither the authors of these papers nor the referees who reviewed them seem to have paid enough attention to references. Yet, proper credit is an essential part of any scientific publication (it is also, in our opinion, synonymous with honesty). Keeping up to date with the ever-growing number of publications is difficult, but it should not keep the authors from using the excellent abstracting services available. And referees, who are experts in the fields of the papers they review, could also pay closer attention. Table I1 includes one striking example. A reference
ANALYTICAL CHEMISTRY, VOL. 64, NO. 12, JUNE 15, 1992
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PLASMA EMISSION SPECTROMETRY
Table I. Books on Plasma Emission/Fluorescence Spectrometry title
Sample Introduction i n Atomic Spectroscopy Atomic Spectroscopy Multielement Detection Systems for Spectrochemical Analysis Environmental Analysis Using Chromatography Interfaced with Atomic Spectroscopy Laser Micro Analysis Laser-Induced Plasmas and Applications Flow Injection Atomic Spectroscopy Handbook of Inductively C o w l e d Plasma SDectrometrv
should also be made whenever excitation and ionization energies are mentioned (...unless the authors found new values, in which case they should emphasize it somewhat!). When results are compared with certified values, the confidence interval of these values should also be included so that the readers can assess the “agreement” themselves. Standard deviations and detection limits should always be associated with a number of replicates or integration time. A definition of the detection limit should also be included since a number of different approaches are widely used. Several pa ers did not satisfy these minimal (and statistically senshe) requirements. Finally, although the pressure is high to publish (especially in academia where “Publish or Perish” is more than ever the sayin of these days of economic recession), authors should not uniuly split their results into several publications, and in any case, should never publish the same results twice. For example, Table 5 of ref C2-36 is identical to Table 3 of ref C2-33 without any reference being made to the latter. An even more appalling example (at least in the previous case, the “replicates” appeared in two different journals) is that Figures 9B and 9A of ref F8 are identical to, respectively, Figures 3A and 3B of ref C1-41, which all appeared within the same volume of the same ‘ournal! The quality of scientific papers, although on average &dy high, would be even higher if everybody, authors and referees, were just a little more attentive. The sub‘ect of detection limits is actually very contentious. It seems that most analytical chemists/spectroscopists use whatever “formula” they feel more comfortable with or that is most currently used (for instance, in chromatograph , it is usually based on peak-to-peaknoise rather than on staniard deviation as in s ectroscopy). “Hence confusion rei ns!”,.as was truly pointelout by Boumans (A4)who publish a senes of papers and tutorials (A4-A7) to clarify the situation and try to convince the community to agree on one definition based on both the signal-to-background ratio (SBR) and the relative standard deviation of the background (RSDB). Although this approach essentially ields the same result as that based on signal-to-noiseratio ( ~ N R )it, carries more information since the signal (strictly the sensitivity obtained from a calibration) and standard deviation which are usually employed to calculate the SNR have both to be ratioed to the actual value of the background which then serves as a reference, and greatly facilitates comparisons between systems. As an assignment (does it show that we are in academia?),the reader is expected to ive a close look at the above-mentioned papers. &oks. Since several books have appeared during the past 2 years, and that it would take too much space to appropriately give an account of their content, we have decided to present the information in the form of Table I which makes reference to detailed book reviews written by experts in the different subdisciplines. Review articles will be found throughout this review in (what we think are) the most appropriate sections. Conferences. Because of the ever-growin number of conferences, there is no way that one or more o the authors can attend them all. Instead, we refer the reader to the ZCP Information Newsletter (edited by Ramon M. Barnes) which regularly publishes abstracts, pertaining to plasma emission spectrometry, from numerous conferences. As well, we strongly recommend that anybody with a certain interest in this field attend THE conference in lasma emission spectrometry which is, without any doubt, #e Winter Conference on Plasma Spectrochemistry held every even year in the United States, and every odd year, its European counterpart occcurs: The European Winter Conference on Plasma Spectrochemistry (obviously held in Europe). Information
d
P
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 12, JUNE 15, 1992
year
book review
J. W. Robinson K. W. Busch and M. A. Busch R. M. Harrison and S. Rapsomanikis
1990 1990 1990 1989
AB, A9 A10, A l l A12, A13 A14-Al6
L. Moenke-Blankenburg L. J. Radziemski and D. A. Cremers, Eds. J. L. Burguera, Ed. M. ThomDson and J. N. Walsh
1989 1989 1989 1989
A17, A18 A19, A20 A21, A22 A23. A24
authors and/or editors J. Sneddon, Ed.
about these (and other) conferences can also be found in the above-mentioned publication.
B. SAMPLE PRETREATMENT Digestion. Matusiewicz (SI)reviewed acid vapor-phase
sample digestion, a technique which offers an elegant alternative to acid digestion of inorganic or organic sample matrices. Acid vapor produced in one vessel is used to attack and dissolve material placed in another one, which reduces the possible introduction of impurities into the samples and blanks. This technique should be greatly speeded up using a microwave oven. Therefore, an evaluation and investigation of vapor-phase microwave digestion of inorganic and organic materials is certainly warranted. FROM NOW ON, UNLESS OTHERWISE SPECIFIED, THE TECHNI UES DESCRIBED WERE USED IN COMBINATION WI H INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION SPECTROMETRY (ICP-AES) USING ARGON AS THE PLASMA, AUXILIARY, AND NEBULIZATION GASES. Botto (B2)reviewed the variety of sample preparation methods which can be used for the multielement analysis of fossil fuels, coals, fly ashes, shales, etc. These include highpressure digestions, microwave digestions, ashing, and oxygen combustion, to name a few. Steps to take during the actual analysis are also detailed, such as the optimization of the instrument, the calibration strategy, and corrections for spectroscopic, physical, and/or chemical interferences. In another comprehensive review, Borsier (B3) described the sample preparation and decomposition procedures which can be used for the determination of major, minor, and trace elements in materials analyzed during geochemical explorations. In particular, full details are given on means to automate the multielement analysis, and at the same time assure reliability and recision. Quality control as well as proper calibrations, ancfcorrections for interferences, are all discussed to this end. Usin a promisin approach, Karanassios et al. (B4) developef a stopped-iow microwave digestion system. The sample, consisting of an aqueous slurry, was mixed with acids on-line and pumped in a coiled Teflon tube installed inside a microwave oven. The flow was then sto ped, the tube was sealed by closing valves on both ends, ancf microwave power was applied for 2 min. This procedure gave precise and, in many caw, quantitative digestions of powdered botanical and biological reference materials. Although still in its infancy, it shows great promise since manipulation of the sample (and therefore contamination) is drastically reduced, and furthermore, it can be readily automated. Selected digestion procedures which appeared in the literature are summarized in Table I1 to illustrate the range of applications. Microwave digestion is obviously the way to go in terms of speed,recoveries and lower contamination. It can be used for almost any type of material. Extraction/Separation. Selected techniques are summarized in Table 111. They were particularly popular for the separation of rare earth elements from a variety of materials. Preconcentration. Dupont et al. (B26)solved the problem of poor recovery of V from Chelex-100 by simply di esting the resin (using microwave digestion, in open vessels7. The determination of V in seawater could therefore be accomplished after preconcentration on Chelex-100, and good agreement was obtained with an independent technique, i.e. coprecipitation/GFAAS. An investi ation of the uptake of metal traces by immobilized 8-hyfroxyquinoline and 8-
9
PLASMA EMISSION SPECTROMETRY
Table 11. Selected Digestion Techniques Used in Conjunction with ICP-AES(Unless Otherwise Indicated) elements
matrix
preferred procedure
comments
microwave digestion with 3:l HN03:HC1 extraction of elements not strongly and 1 mL of water for a maximum bound to silica (complete dissolution of 20 min; solutions were decanted prior not reauired); any amount of water analysis improved recover-ies, comparable to (or better than) hot-plate methods, but with greater precision microwave digestion with aqua regia Cd, Cr, Cu, Fe, Mn, soils, sediments, complete dissolution was not a Pb, Zn sludges during 65 min; solutions were filtered requirement; faster than conventional prior analysis acid extraction; does not refer to B5, which, except for Cr, accomplished a faster extraction of a greater number of elements from sediments up to 23 elements sampling filters, filters refluxed with 3 mL aqua regia microwave digestion compared with ashes, dusts, during 3 h; microwave digestion with several open-vessel digestions: faster; paints aqua regia/HF (dusts, ashes) or better recoveries (except for As if HF HN03 (paints) for 10 min has to be evaporated); methods successful with reference materials barite, strontianite reflux in covered beaker with NH40H most of the elements are found in the Ba, Sr, Be, Co, Cr, Cu, La, Ni, V, Yb, and EDTA-2Na (3-4 h); filter; wash two fractions (EDTA-2Na, residue); Zn with hot 5% NH,OH; residue ignited, results were not compared with an independent technique: accuracy was fused, etc. not assessed Al, Ca, Fe, Mg, P, zirconia, A1 nitride fusion with Na2C03and NaTB407; the fusion is efficient for both samples; Si, Ti ceramics dissolution in 6 M HCl; diluted to 3 HC1 digestion in closed vessels adds M HC1 less salt but only quantitative for A1 nitride; fast H2S0,/ (NH4)2S0, digestion for zirconia Co, Cu, V, Mn, Mo, ferrochromium, open-vessel microwave digestion with microwave procedure required 10 min vs Ni, Si, Ti, Al, Cr ferromanganese H2S04/H3P04(+HNO, for 2-3 h by conventional techniques; ferromanganese) accurate results (compared with flame I AAS and neutron activation analysis) major, minor, trace meteorite digestion in Teflon bomb with aqua complete sample dissolution achieved regia/HF for 6-8 h; addition of with minimum loss of volatile analytes; ultrasonic nebulization was to complex HF; original used for its detection power and sample diluted 800-fold freedom from clogging Al, As, P silicon digestion in PTFE beakers with a modified digestion procedure required mixture of HN03/HF/H202; for the determination of As by evaporation to near dryness and hydride generation DCP-AES; results dissolution with HCL for As in agreement with GFAAS B biological materials digestion with H2S04at 100 OC for 1 h; calibration with H3B03 standards was addition of H202before dilution accurate for other B species (by DCP-AES); loss of sensitivity for >50 mg B/L digest high-purity silica digestion with HN03/HF and 4% B Si evaporated as SiF, but loss of B as BF3 prevented by formation of a mannitol; evaporation to 0.5 mL; repetition of the whole process until stable cyclic ester with mannitol; matrix-matched standards used for complete dissolution analysis by DCP-AES; detection limit = 0.76 pg/g Au geological SRMs digestion in polypropylene tube with 2.5-g samples and background correction aqua regia and then HCl; filtration produced the most accurate and dilution DCP-AES results; matrix effects/interferences were checked; detection limit = 6 pg/L in water or 2% HC1 Si, Al, Fe, Mg, Mn, geological SRMs automated alkaline fusion of 6 samples 100-400-mg sample depending on the Ca, Ti, Na, Sr, Zn, simultaneously; or microwave matrix and dissolution technique; in Ba, Rb digestion with HF; excess HF either case, the maximum preparation complexed with time was 25-30 min; internal standardization (Y)was used AI milk powder precharring of 5-g sample in tall beaker borosilicate glass was a suitable material additives with Bunsen burner; 16-h charring in for the beaker (lowest A1 content muffle furnace compared to 4 other materials) transition, alkalis, alkaline earths
sediments
hydroxyquinoline-5-sulfonic acid on polymeric sorbents @olyatyrendvin lbenzene copolymer and an anion exchange resin) was carrieBout (B27). These solid supports which contain much less metal impurities than silica-based supports, resulted in lower blanks and could be used for the preconcentration of metal traces from environmental samples. Although not all recoveries were quantitative, corrections based on the yield for known samples, allowed the determination of several metals down to a few micrograms er liter. The system, however, was not tested with stanfard reference materials (SRMs).
ref B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
Two separations/preconcentrationsusing coprecipitation were also reported (B28, B29). One (B28) involved precipitation with Ga hydroxide, of 14 trace metals in 10 mL of seawater, and re-dissolution of the recipitate in 50 p L of 1 M HNOBwhich was then aspirated y! the nebulizer in ICPAES. Detection limits ranged between 0.02 (Cu, Zn) and 3 pg L (Mo) for this 200-fold preconcentration procedure. The ot er paper (B29) described the determination of 10 trace elements in high-purity molybdenum and molybdenum trioxide, b coprecipitation with La hydroxide. The pH was adjustelwith ammonium hydroxide to simultaneously pre-
h
ANALYTICAL CHEMISTRY, VOL. 64, NO. 12, JUNE 15, 1992
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PLASMA EMISSION SPECTROMETRY
Table 111. Selected Extraction/Separation Techniques Used i n Conjunction with ICP-AES (Unless Otherwise Indicated) elements B
matrix water samples, soil extracts
detection limit” 2 Pg/L
comments
ref
3 mL of HF added to 75 mL of sample to convert B B18
to BF,- ions which are then extracted with an anion-exchanger into xylene 1-g sample digested with H2S04and HF, and dried; R E E s , ~Y, Sc rocks after alkaline fusion, extraction with 4% m/v TOPOc in isobutyl methyl ketone or toluene for determination of REEs, Y,and Sc; back-extraction with 6 M HCl possible (not for SC) open-vessel digestion with HF and HClO,, taken standard reference Er almost to dryness; diluted with 0.6 M HCl before materials (geological and passage on strongly acid, cation exchange resin; biological) major elements washed with 3 M HC1/20% ethanol; REEs (including Er) eluted with 7 M HNO, dissolution in 7 M HNO, and evaporation down; 0.1 pg/L (Yb) to 9.5 pg/L uranium REEs uranyl nitrate crystals dissolved in 4 M HNO, (Ce) (10 g sample in 25 mL) and extracted with tributyl phosphate in CCl,; traces of U then extracted with T O P 0 in CCl,; aqueous phase analyzed dissolution of Nb with HF and HNO,; taken to Mg, Cr, Mn, Ti, high-purity Nb dryness and dissolved in 5 M HC1/7 M HF; W, Mo, Fe, Ta solution passed on strongly basic anion-exchange resin; elution of most traces with 5 M HC1/7 M HF; separate elution of Nb with 7 M HC1/0.2 M HF: final elution of Ta. Fe with 3 M H2S04/0.1%Hz02 9 REEs sediment (proposed 0.015 gg/g (Eu, Yb, Lu), 0.15 digestion with HN0,:HF (1:9) and then HCl; dry residue redissolved in 1.75 M HC1: solution reference material) rg/g (La, Gd, DY),0.3 rg/g passed on cation-exchange column to separate (Ce, Nd, Sm) the REEs from Fe, Ca, etc.; REEs eluted with 8 M HNO,; taken to dryness, etc. digestion with HNO,/HF, and HC10,/HN03 in REEs rock standards bombs; dry residue redissolved in 2 M HCl; solution passed on cation-exchange column to separate the REEs from Fe, Ca, etc.; REEs eluted with 8 M HNO, 0.3 pg/L (Mn, Ti) to 11 pg/L conversion of Si to the fluoride by adding HF; 1% Fe, Al, Ca, Mn, silicon, chlorosilanes mannitol used to prevent evaporation of BF,; P, Ni, Ti, Cu, (P) evaporation to dryness; cycle repeated 3 times; Cr, B dissolution of residue using HNO,
B19
B20
B21
B22
B23
B24
B25
aBased on 3 times the standard deviation of the blank. bRare earth elements. cTrioctylphosphine oxide.
cipitate Cu, Co, Ni, and Zn as their amine complexes. ICPAES detection limits ranged between 0.03 pg/g (Zr) and 1.9 pg/g (Cu) in molybdenum.
C. SAMPLE INTRODUCTION C1. Llquld Sample Introductlon
Fundamentals. Water Loading. A study (Cl-1) looked at the drop size distribution of pneumatically-generated aerosols as they passed thro h a Scott-type doublepass spray chamber. Eva oration an? es ecially droplet coalescence mainly affectel the size distrigution right in front of the nebulizer, while impaction against the inner wall of the inner tube of the spray chamber resulted in important losses in the middle of the spray chamber, and inertial losses were most significant at the bottom of the spray chamber. Gravitational -1 became important when the nebulizer flow rate was low. Any factor (surface tension, viscosity, etc.) affecting the mean diameter of the droplets would enhance one or more of these loss rocesses. These findings should be important for the deveyopment of more efficient spray chambers. Clifford et al. (Cl-2)described a dual-beam, light-scattering interferometer which they applied to the characterizationof aerosols from various nebulizers/Scott double-pass spray chamber systems. The instrument elded Sauter mean diameters comparable to those obtainerby laser Fraunhofer diffraction. However, the proposed technique allowed the direct, rapid and simultaneous measurement of spatially-resolved droplet size and velocity distributions. Nixon (Cl-3) studied the desolvation of an aerosol generated by a cross-flow nebulizer/barrel-type spray chamber with a heated tube/condenser system. In these conditions (unfor448R
ANALYTICAL CHEMISTRY, VOL. 64, NO. 12, JUNE 15, 1992
tunately the exact curvature of the “gently curved” heated tube was not specified by the author, and the referees did not insist that this detail might be essential to the repeat of these experiments), the water content of the aerosol was reduced by 84% with only a 9% reduction in nebulization efficiency. In the normal analytical zone (NAZ) (see C1-4 for this terminology), desolvation resulted in a shift to lower observation heights and, especially, an enhancement of emission lines with excitation energies (including the ionization energy for ionic lines) lower than the dissociation energy of water. Whereas in the initial radiation zone (IRZ), all lines were significantly enhanced whatever their excitation energy. Both ionization and excitation temperatures were enhanced u n desolvation, regardless of the hei ht in the plasma. Desocation bro the plasma closer to kcal thermodynamic equilibrium (L E) conditions, especially in the IRZ. Supporting findings were reported by Olesik and Den ((21-5)where the Mg I1 to M I emission intensity ratios did not change significantly with &e central gas flow rate for a dry aerosol whereas huge variations were observed with a wet aerosol. Olesik and Fister (Cl-6) specifically studied the effects of incompletely desolvated droplets on intensities and observed that vaporizing droplets induced changes in ionization and/or excitation of free analyte atoms and/or ions in their vicinity, resulting in large signal fluctuations. The number and size of these incompletely desolvated droplets could be decreased by increasing the power, decreasin the nebulizer flow rate, or using a higher observation heigit. These effects are important for all time-integrated measurements because, under inappropriate operating conditions (i.e. producing a large number of incompletely vaporized droplets) a significant error may be introduced. They also apply to ion/atom emission intensity
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PLASMA EMISSION SPECTROMETRY
ratios since the ion radial emission profile was observed to widen in presence of a va orizing droplet whereas that of the atom became narrower Pc1-7). The effect of aerosol mass transport rate on responsivity (Le. relative emission or fluorescence per mass of analyte introduced) in AES and AFS was investigated (C1-8). Ionic emission responsivity decreased as aerosol mass transport rate increased, while ionic fluorescence responsivity remained constant or increased under the same conditions, demonstrating a decrease in the fraction of ions being excited and undergoing emission, rather than an actual decrease in the number of ions produced in the plasma. Canals et al. (C1-9) characterized aerosols generated with concentric and crass-flow nebulizers and found that the Nukiyama-Tanasawa (N-T) equation alwa s overestimated the mean aerosol drop size; and that it p r d i c t d larger aerosols with some organic solvents than with water, while experimental evidence showed the reverse. Also, nebulizers formed finer aerosols as the crosssectional area of the nebulizing gas decreased. Obviously, nebulizers and spra chambers (in atomic spectrometry) should be optimizedYusin the droplet size of the aerosol produced instead of the d-T equation. Ivaldi and Slavin (Cl-10)proposed a protocol to test the performance of nebulizers. A "performance index" (PI) was calculated by averagin 4 RSDs from 4 sets of 10 measurements each, in fixed con&ions, after a 1-h warm-up period, while aspirating a 10 mg/L Mn standard solution containing both 1% HNO, and 0.04% Triton X-100.The surfactant reduced signal fluctuations by preventing dissolved air in the solution from forming air bubbles. In fact, addition of a surfactant was as efficient as de-gassing the solution. The PI is a simple approach to test the quality and reliability of performance of nebulizers. Another interesting observation made by the authors was that an Ar line followed the inverse behavior of that from the analytes when the nebulizer was malfunctioning. Monitoring Ar in parallel to the analytes throughout analyses is therefore a sim le way of continuously checkmg the performance of the neburizer. For the first time, the primary aerosol formed by an ulas well trasonic nebulizer (USN) was characterized (C1-11), as the tertiary aerosol (so far, only the latter had been studied). Surprise! The USN did not form smaller droplets as more energy was applied to it. In fact, an increase in liquid flow rate resulted in a finer tertiary aerosol. The primary aerosol generated by the USN had a substantially broader size distribution than that produced by a Meinhard concentric nebulizer, but also a much higher particle density, resulting in a greater number of appropriately sized droplets reaching the plasma than for a pneumatic nebulizer. Wiederin and Houk (CI-12) characterized the aerosol produced by a direct injection nebulizer (DIN). Under the same operating conditions (0.5 L/min nebulizer gas and 100 pL/min sample flow), the Sauter mean diameter of the aerosol produced by the DIN was smaller than with a Meinhard C concentric nebulizer. In typical operating conditions, however, the aerosol from a concentric nebulizer/Scott-type spray chamber had a smaller mean diameter but with a much lower transport efficiency. The 100% transport efficiency of the DIN makes elimination of a spray chamber possible without sacrificing precision or sensitivity. Therefore, we predict an increase in lnterest for this type of liquid sample introduction system. Organic Solvent Loading. Olesik and Moore (C1-13) studied the effect of organic solvents in concentrations
