Atomic absorption, atomic emission, and flame emission spectrometry

Anal. Chem. I W Q ,62, 303R-324R (M25) RsSIIWSWn, K. m. chem.1989, 3 5 , 260-264. (M26) Hasagawa, M.; Dol, K.; Baba, S. Ckh. Chkn. Acta 1988, 776, 207-212. (M27) SetCheH, K. D. R.; Suchy. F. J.; Welsh, M. 6.; Zhnmer-Nechemlas, L.; HwM, J.; Ballstrerl, W. F. J. Ch?.Invest. 1988, 8 2 , 2148-2157. (M28) Lam, S.; Chan, H.; Le Rlche, J. C.; Chan-Yeung, M.; Salari, H. J . A m Ckh. I-. 1988, 8 7 , 711-717. (M29) Duncan, M. W.; Compton, P.; Lazarus. L.; Smythe, G. A. N . Engl. J. W .1988, 379, 136-142. (M30) Bdt, M. J. 0.; Stellaard, F.; Skin, M. D.; Paumgartner, G. Clin. Chim. ACte 1989, 787, 87-102. (M31) Vandoputte, D. F.; Van Grleken, R. E.; Foets, B. J. J.; Misotten, L. Bbmd. En-. Mss specbwn.1989, 78, 753-756. (M32) ONelll, H. J.; Gordon, S. M.; ONelll, M. H.; Gibbons, R. D.; Szldon, J. P. C6h. chdm.1988, 3 4 , 1613-1618. (M33) S W , J.; Osuga, T.; Matsuwa, K.; Mahara, R.; Tohma, M.; Tanaka, N.; Mateuzakl, Y.; Mlyazakl, H. J. L/pH Res. 1989, 3 0 , 1233-1242. (M34) Weydert-l.lul)shebe6rtwt, S.; Karlagenls, G.; Renner, E. L.; Preislg. R. J. Rm. 1989, 3 0 , 1673-1679. (M35) J a b , F.; Declal. M.; Hemdon, D. N.; Wolfe. R. R. kletabdkm 1988, 3 7 , 330-337. (M36) shew, J. H. F.; Wolfe, R. R. Swgery 1988, 703, 148-155. (W7) MOM, K. J.; Montandon, C. M.; Hachey. D. L.; Boutton, T. W.; Klein, P. D.; C. J. Appl. Fhyslol. 1989, 66, 370-378. (M38) Horn, L. J.; Yang, R. D.; Matthews, D. E.; Blstrlan, 8. R.; Bier, D. M.; Young, V. R. Am. J. C h . Nub. 1988, 48, 1010-1014. (W9) coctk#a,J.; Metthews, D. E.; Hoerr, R. A.; Bier, D. M.; Young, V. R. Am. J . C h . Nub. 1988, 48, 998-1009. (WO) Thompson, 0. N.; Pacy, P. J.: Menm, H.; Ford, 0.C.; Read, M. A.; K. N.; HaHidey, D. Am. J. phyelol. 1989, 256, E631-E639. ( H I ) Thompson, G. N.; Paw, P. J.; Ford, G. C.; Menttt, H.; Halliday, D. .fur. J . C6h. Invast. 1988, 78, 639-643. (W2) Irving, C. S.; Malphus, E. W.; Thomas, M. R.; Marks, L.; Klein, P. D. Am. J . Cyn. Nub. 1988, 47, 49-52. (W)Karnaukhova, E.; Nlessen, W. M. A.; Tjaden, U. R.; Raap, J.; Lugtenburg, J.; van der W f , J. Ami. 8k&em. 1989. 787, 271-275. (W)F o m , S. J.; Bler, D. M.; Matthews, D. E.; Rogers, R. R.; Edwards, B. 6.; tiegler, E. E.; Nelson. S. E. J . psdletr. 1988, 713, 515-517.

m,

(M45) Thompson, (3. N.; Waiter, J. H.; Bresson, J.I.; Ford, 0.C.; Bonnefont, J. P.; Chalmers, R. A.; Saudubray, J. M.; Leonard, J. V.; Haillday, D. J. Pediatr. 1989, 775,735-739. (M46) Waiter, J. H.; Thompson, 0.N.; Leonard, J. V.; Heatherlngton, C. S.; Bartlett, K. CUn. Chim. Acta 1989, 782, 141-150. (M47) Millington. D. S.; Maltby, D. A.; @le. D.; Roe, C. R. I n SpUmk and Applications of Stabk Isotoplce&Labelled Compounds 7988, Balllle, T. A.. Jones, J. R. Eds.; Elsevier: Amsterdam, 1989; pp 189-194. (M48) Bowyer, B. A.; Fleming, C. R.; Haymond, M. W.; Mlles. J. M. Am. J . C M . Nub.. 1989, 49. 618-623. (M49) Esteban, N. V.; Yergey, A. L.; Liberato, D. J.; Loughlln, T.; Lorlaux, D. L. Bbmed. Envkon. Mess Spectrom. 1988, 15, 603-608. (M5O) Kraan, G. P. 6.; Chapman, T. E.; Drayer, N. M.; Nagel, 0.T.; Wolthers, 8. G.;Colenbrander, 8.; Fentenw-van Vllssingen, M. Blomed. Envkon. Mess Smctrom. 1989. 78. 662-667. (M51) Vie;happer, H.; Nowotny, P.; Waldhaeusl, W. J. SteroM Bkchem. 1988, 2 9 . 105-109. (M52) Koopman, B. J.; Kuipers, F.; Bijleveld, C. M. A.; Van der Molen, J. C.; 143-156. G. T.; Vonk, R. J.; Wolthers, B. G. Clin. Chim. Acta 1988, 775, Nagel, (M53) Avogaro, A.; Brlstow, J. D.; Bier, D. M.; Cobelli, C.; Toffolo. 0.D&betes lg89. 38. 1048-1055. (M54) Mchriahon, M. M.; Schwenk, W. F.; Haymond, M. W.; Rlzza, R. A. DkbeteS 1989, 3 8 , 97-107. (M55) BaUUe. T. A,; Jones. J. R., Eds. Synthesis and Applkxtrbns of Isotopia l l y Labelled C.bWOlItlOk, 7988; Proceedings of the Thkd International Symposium; Elsevler: Amsterdam, 1989. (M56) Hillman, L. S.; Tack, E.; Coveli, D. 0.;Vlelra, N. E.; Yergey, A. L. P e t . Res. 1988, 23. 589-594. (M57) McMillan, D. C.; Preston, T.; Taggart, D. P. B b m d . Envkon. Mess Spectrom. 1989, 78, 543-546. (M58) Dever, M.; Smith. J. E.; Hausler, D. W. Clin. Chim. Acta 1989, 787. 337-342. (M59) Faheather-Tait, S. J.; Portwood, D. E.; Symss, L. L.; Eagles, J.; Minski. M. J. Am. J. Clin. Nub. 1989, 49. 151-155. (M60) Javltt. N. 6.; Javltt, J. I . Blomed. Environ. Mass Spectrom. 1989, 18, 624-628.

Atomic Mass Spectrometry David W. Koppenaal Pacific Northwest Laboratory,' P.O.Box 999, MS P8-08, Richland, Washington 99352

INTRODUCTION AND SCOPE This is the second fundamental review on the currently topical sub'ect of atomic mass s ectrometry. Following the format of tke initial survey on t k s subject (I),the intent of this review is to assess the scientific activit ,as evidenced in the published literature, in the growing fie d of atomic mass s ectrometry. Boundary limits for this review are set by title efinition, the aims of this journal, and the late 1987-late 1989 time period. Atomic mass spectrometry is defied as the mass spectrometric measurement of atomic ions, for the primary purpose of elemental and/or isotopic compositional determination. The atomic mass spectrometry term is preferred over the more widely used and all-encompassing inorganic mass spectrome or elemental mass spectrometryterms, as it more clearly in icates the elemental and isotopic emphasis of this review while excluding other legitimate inorganic mass spectrometry topics such as organometallic and chelate compound structure identification, metal cluster ion formation and reaction studies, and gaseous metal chemistry, all of which are active1 investigated by using mass s ectrometry techniques (aniwhich are reviewed elsewhere 3)). The atomic mass spectrometry label is also grammatically parallel with terminology for other analytical techniques based on atomic phenomena (i.e., atomic absorption, atomic emission, and atomic fluorescence). Consistent with the aims of thisjournal,

i

B

9

&,

'0 rated for the U.S. Department of Energy by Battelle Memorial K s t i t u t e under Contract DE-AC06-76RLO 1830. 0003-2700/90/0362-303R$09.50/0

this review places emphasis on developments and applications of atomic mass spectrometry for quantitative analytical purposes. This review is technique oriented and organized. Primary atomic mass spectrometric techniques reviewed include spark source, glow dischar e, inductively coupled plasma, stable isotope ratio, therm$ (surface) ionization, laser microprobe, resonance ionization, accelerator, and secondary ion mass spectrometry methods. These sub'ecta are given the acron SSMS, GDMS, ICPMS, SIRMS, h S , LMMS, RIMS, and SIMS, respectively. Miscellaneous tecnhiques that fit within the atomic mass spectrometry definition or relate to it are also included where appropriate. Mechanistics of this review are based on a computerized Chemical Abstracts search of titles, keywords, and abstracts of literature published from late 1987 to late 1989. Government reports, unpublished conference proceedings, and obscure forei journal references are in general not cited in this review. &re foreign journal references are cited, a Chemical Abstrads accession number is also given. Over 2300 literature citations were screened for this review; as directed by the readership and editorial desires of this journal this review is somewhat critical and selective in its coverage. It is the author's hope that this approach will be of most use to the journal readers. Instrument refinements, technique developments, analytical applications, and technique status reports are all covered in this review. Surveys of the type and scope of analytical applications are judged by this reviewer to be t!.: ultimate measure of a techniques utility and e cceptance by the ana0 1990 American Chemical Society

303 R

ATOMIC MASS SPECTROMETRY

lytical and scientific community. Accordingly, for each atomic mass spectrometric technique, a survey of unique, innovative, and typical applications is presented. Due to space constraints, these ap lication surveys are typically presented in tabular format. getailed application reviews, organized by generic application subjects, are available in the alternate-year application reviews of this journal. For the trace element analyst, it is recommended that this review be perused in conjunction with the companion reviews in this issue entitled “Emission Spectrometry”, by P. N. Keliher, H. Ibrahii, and D. J. Gerth, and “Atomic Absorption, Atomic Emission, and Flame Emission Spectrometry”, by J. A. Holcombe and D. C. Hassel. For the mass spectroscopist, this review and the generically titled Mass Spectrometry review (also in this Fundamental Review issue) should cover the mass spectral analysis field quite effectively.

A. BOOKS,CONFERENCE PROCEEDINGS, REVIEWS, AND COMPARATIVE STUDIES The vitality of the atomic mass spectrometry field is evident from the number of recently published books, proceedings, reviews, and intertechnique comparison studies. Literature of these forms has obviously proliferated over the review eriod. This section summarizes this activity, beginning with ook releases. Although reviewed (as a page proof copy) in the last Fundamental Review under this title, the formal publication of the text Inorganic Mass Spectrometry in 1988 merits its mention again in this review (AI). This text, with excellent subject cha tern on SSMS, GDMS, LMMS, ICPMS, SIMS and isotope Silution mass spectrometry (IDMS), is worth keeping within easy reach (it is the first new inor anic mass spectrometry book in almost 20 years). Two recentgbook reviews give this timely publication high marks (A2, A3). Other recent books have concentrated on individual atomic MS techniques. Two such books are the proceedings publications of the 6th Secondary Ion Mass Spectrometry Conference (A4)and the 4th International Resonance Ionization Spectrosco y Symposium (A5). Both volumes consist of short (2-4 pages7 “snapshot” articles describing the most recent research in these subject areas. Also released in the RIMS area was a text devoted to the fundamentals of resonance ionization spectroscopy, including RIMS, by two of the technique innovators (A6). Moenke-Blankenbur authored a new text entitled Laser Microanalysis ( A n ; ciapters on LMMS and laser ablation ICPMS are included, as well as a good discussion of laser-solid interactions and related phenomena. The ICPMS technique has matured rapidly enough to merit a new book entitled Applications of Inductively Couple Plasma Mass Spectrometry (A8);chapters on geological, environmental, isotope ratio, and isotope dilution applications are notable in this work. Other topical conferences resulted in special periodical proceedings issues. The fourth conference on AMS had its proceedings published in a special journal volume (A9) comsed of full-length research papers of generally high quality. ass spectrometric methods for trace-element analysis was the subject of a symposium held in Germany in late 1987, with the resultant papers being assimilated in a separate journal volume (AIO). This volume includes apers on ICPMS, GDMS, SSMS, IDMS, SIMS, and LdMS. Accounts of ICPMS research in Japan are included in a recent issue of Muss Spectroscopy (AI I), although no English translations are yet available for these apparently interesting papers. The Royal Society of Chemtry has mcluded inorganic mass spectrometry, in combination with X-ray fluorescence spectrometr in a series of Atomic Spectrometry Updates (A12, A13). is series of reports abstracts both literature and conference abstracts, and the relevant cover e of atomic mass spectrometry to ics includes ICPMS, GDMX RIMS, SIRMS TIMS, and SSkrS. The reviews of ICPMS and GDMS ii especially thorough in these u dates. Numerous comparative stuzies of atomic mass spectrometric techniques, both with different mass s ectrometric methods and with other trace analysis metho&, have also fluorished and are of note in comparing and contrasting the capabilities of these various anal tical tools. Three MS techniques (GDMS, SSMS, and SIhS) were studied for the ultra-trace analysis of refractory metals in a five-part series (AI4-AI8). Refractory metal analysis was also the subject of another assessment of mass spectrometric and other ana-

E

K

‘&I

304R

ANALYTICAL CHEMISTRY, VOL. 62, NO. 12, JUNE 15, 1990

lytical techniques (AI9). A review of ceramic materials analysis also included mass spectrometric techniques (A20). Various atomic MS methods (TIMS, SSMS, ICPMS, with IDMS) were reviewed for application to La, U, and Th determination in geological samples (MI)and are compared with radiochemical methods of analysis. Geochemistry and cosmochemistry are the applications for another review of mass spectrometry for inorganic and isotopic characterization (A22). A similar review with emphasis on food analysis is also available (A23). Nuclear science and mass spectrometry have enjoyed a symbiotic development history; De Laeter has reviewed the role of mass spectrometry in radioactive nuclide identification, half-life determinations, and fission process studies, among other contributions to nuc ear chemistry and physics (A24). Element-specificreviews inc uding atomic MS consideration include those covering P b ( A B ) and Cd (A26). Finally, ion source characteristics, sample analysis requirements, and analytical figures of merit are subjectively compared in a discussion of SSMS, GDMS, LMMS, and SIMS for solids analysis (A27).

’I

B. SPARK-SOURCE MASS SPECTROMETRY S ark-source mass spectrometry has played a unique role in t i e history of atomic mass spectral analysis. It provided the analytical chemist with his first truly multielement (and isotopic) trace analysis tool. It opened the e es of many trace analysts (including this reviewer) to the tenefits of mass spectrometric analysis for trace-element determinations. Finally, it has provided a transition from the “old” (pre-1960) to the “new” (post-1975) era of atomic mass spectrometry. Although maligned for its quantitation complexity and poor reproducibility, the role of SSMS has been a noble one. With the growing emergence of modern atomic MS techniques (ICPMS, GDMS, LMMS), however, this role is diminishing. While numerous application reports were published over the review period, fundamental studies or instrumental developments were notably scarce. Of the latter category, two studies were published that addressed the SSMS nemesis of relative sensitivity factor (RSF) determination and use. In relation to iron and steel alloy analysis, the use of groups of RSFs, dependent on sample matrix, was demonstrated to yield results for many elements within a factor of 1.4-1.6, without prior calibration in every analysis case (BI). In another report, theoretically deduced ionization coefficients were calculated from empirical RSF data and employed in the analysis of Cu samples (B2),yielding typical SSMS results of *30% accuracy. Photoplate calibration also continues to be addressed to some extent in SSMS. Densitometry and photoplate exposure linearity errors were examined and minimized by using the Hull equation and least-squares optimization methods (B3). Another photoplate calibration procedure was suggested based on the fragmenting of a Churchill two-line curve into component parts and subsequent polynomial fitting of each se ment (B4). Electrical detection, which never reached wile acce tance in SSMS, was studied by another group, who attriguted the Dresence of diffuse electrical detection peaks to reflected io& (B5). One of the more interesting SSMS Dublications discussed the development and applic&ion of solution-doping rocedure for the analysis of subnanogram amounts of disaoged analytes (B6). According to the described procedure, microliter amounts of liquid sample were eva orated onto a graphite electrode rior to analysis. Reduce measurement times, photoplate Eackground, and polyatomic or isobaric interferences were claimed with the technique. Detection limits of 5-20 pg and a precision of 1-5% rsd at concentrations 21 ng were also documented. The subject of thin-layer SSMS analysis was also advocated by another group (B7). In regard to SSMS applications, the most frequent use of the technique was in the area of h-purit materials analysis. Materials analyzed by using SS S inclu ed Cu (B8,B9), Co (BIOI, H3B03( B I I ) ,Zircaloy and Te (BI2),Ga/GaAs (BI3, B I 4 ) , W (BI5), Hf (B4),Hg (BI6), and H I (BI7).Two reports of botanical sample analyse3 were p u b b e d , one using isotope dilution to determine Hg (BI8),and the other reorting the determination of -30 elements by SSMS (B19). application to geological samples remains popular (B20-B22), althou h claims regarding its accurac were debated (B20,B23). %inally,the application of SS& to paint and pigment analysis was reported (B24). In contrast to

B

k f l

ESMS


expressed surprise with the use of IDMS techniques with SSMS (A13), IDMS has been (and remains) opular with the spark-source practitioners. Examples of PDMS use were prominent in many of the above applications (R6, R9, R18, R22, ,925).

C. PLASMA SOURCE MASS SPECTROMETRY The use of plasmas as ion sources appears to many to be a recent analytical development; in actuality, glow, corona, and spark discharges were explored and utilized as ion sources decades ago. The widespread recognition of the utility and benefits of plasma ion sources is attributable to the recent and impressive developments in inductively coupled plasma and glow discharge mass spectrometry (ICPMS and GDMS), both of which are receiving intense attention by the analytical community. ICPMS has passed through a remarkably short adolescence period and is now in a mature stage with a prolific record of instrument acquisitions and real-world application reports. GDMS is experiencing a somewhat slower growth compared to ICPMS, hut evidence of real maturation is mounting and significant activity and progress is expected within the next few years. Alternative plasmas using different support gases or excitation modes also continue to he investigated for MS application. This section reviews these developments. 1. Inductively Coupled Plasma Mass Spectrometry. Reuiews and Assessments. Activity in the ICPMS field over the review period has been nothing short of remarkable; indeed, ICPMS was recently identified as one of the "hottest" areas in science (CZ, C2), one of only two analytical disciplines to he so recognized. As expected with any rapidly developing technique, a number of technique reviews became available. Houk and Thompson present the most comprehensive summary of recent developments (CY)and include authoritative discussions on ion sampling theory, interference effects, and isotope ratio possibilities and constraints. A more recent review by Hieftje and Vickers (C4) views ICPMS development as related to an ICP-OES background, a situation that is familiar to many current ICPMS users. The nearly exponential growth of ICPMS publications since the mid-1970s was noted in this review. A paternal review by Gray (C5) nicely introduces a new book on ICP applications (A8). Other general reviews are also available but are more didactic and less critical in nature (C6, C7). Douglas offers a personal viewpoint on the development of ICPMS and also includes some very interesting descriptions of previously unpublished experiments including the RF biasing of interface cones to control ion energy, the use of bent RF-only quadrupole rods to eliminate photon noise, and the investigation of a triplequadrupole MS instrument with an ICP ion source as a means to reduce molecular ion interferences (C8). A need for head-to-head comparisons of ICPMS with other atomic spectrometric techniques has been expressed (C4),and a t least one such comparison was published. In this study (C9) ICPMS was compared with ICP-OES, ICP-AFS, and AAS, using near ideal comparison samples (low-dissolvedsolids granitic groundwaters). ICPMS was used for more

elements, at lower concentrations, than the other comparison techniques; according to the evaluation criteria set forth in this work, ICPMS results compared well with those from ICP-OES and AAS. The lack of other such studies may he due to the inability of other techniques to effectively compete with the overall capabilities of the ICPMS method. Such assessments would nonetheless be useful in clarifying the complementary roles of the various methodologies; their critical comparison and presentation are thus encouraged. Fundamental Studies. A better understanding of ion sorcery and gas dynamics in atmospheric-pressure plasma ion sampling has been the most significant fundamental achievement over the last few years. Much of the early empirical success found with ICPMS now has a theoretical hasis on which an understanding can be formulated and new improvements can he rationalized and tested. Douglas and French applied free-jet expansion and molecule beam sampling theory to ICP ion sampling (CZO).They illustrate, using this theory and appropriate calculations, that the composition of the plasma is effectively frozen in the initial expansion and that proper skimming of the free jet will result in preservation of the ion composition of the plasma. Experimental verification of this sampling theory was provided in an elegant experiment by Houk and co-workers (ClZ),who showed little neutral Na or excited Ba+ fluorescence in the zone of silence of the free-jet region, substantiating the fact that little ionelectron recombination or collisional excitation occurs in this region. On the other hand, the same measurements show appreciable collisional heating and excitation in the Mach disk and barrel shock regions of the free jet. The degree of this reheating was surprisingly high-approximately 2200 K in the Mach disk (indicating reheating to almost half of the plasma source temperature). These observations clearly underline the importance of proper sampler-skimmer cone separation, a fact that was photographically demonstrated in an accompanying article by Gray (CZZ), wherein clear visualization of the free jet, Mach disk, and barrel shock and their spatial relationships relative to the skimmer (at different expansion chamber pressures) can be obtained. Practical ramifications of the ion extraction and gas dynamics involved in ICPMS sampling are principally related to deleterious matrix-induced effects and mass response. A model that explains the observed mass-dependent interference effects was proposed by Gillson et al. (CZ3). Their model is based on space-charge repulsion effects in the skimmer region and skimmer-ion optics region. Higher mass analytes were shown to yield higher pleasured ion currents on-axis than lighter mass ions, mdlcating space-charge-induced defocusing of the lighter analytes. In another study, however, the degree of such suppression was shown to he somewhat dependent on skimmer orifice diameter and first extraction lens potential (CZ4), pointing to the fact that ion sorcery effects still persist and still need delineation. Overall, however, this "gray area" between the ICP source and the quadrupole MS is becoming less and less of a maglcian's secret. Continuing improvements should result in amelioration of the negative effects and optimization for full-range malyte determination. Any experienced comparison of ICPMS with optical emission methods results in a tacit recoenition that the s m d e is being thrown at (and in) the instkmentation with (he former technique. Thus, solids deposition around cone apertures has been a topic of pragmatic and fundamental interest. The monitoring of expansion chamber pressure was shown to mimic salt deposition processes (CZ5). As this and other studies ( C I S ) have shown, salt deposition is dependent on operation parameters (nebulizer flow rate, ICP power, etc.) but not always in a predictable fashion. Both of these studies conclude that a steady state between solids deposition and erosion can generally be reached, allowing useful data acquisition for most sample types. Efforts to circumvent this problem have also heen made, however, using techniques such as flow injection (CZ 7, CZ8), complexation/preconcentration (C19),or ion exchange (C20) to eliminate or minimize dissolved solids in inherently high-solids samples (e.g., brines, urine, AI digests). Other work was directed at use of high-solids nehulizers (C21) or slurry nebulization (C22, C23) to test the tolerance of the t.eehnique to solids-rich solution samples. Approaches to reducing plyatomic ion or other interference effects were also published. Elimination of CI interference in the determination of Se was made possible with sample ANALYTICAL CHEMISTRY. VOL. 62. NO. 12. JUNE 15. 1990 * 305R


prechemistry (C20). Repositionin the sample orifice-to-ICP distance (to approximately 35 mmf along with low RF power and high aerosol gas flows was shown to facilitate determination of K isotope ratios, generally difficult in ICPMS due to the resence of intense Ar ions in the mass spectral region arounc?m/z 34-41 (C24). Polyatomic ions associated with the ICP Ar support gas were reduced in another study, taking advantage of the addition of organic solvent (propanol) or a molecular gas (N2 or 02),and the higher as temperatures available wth the use of these agents to enabe determination of As and Se at m / z 75, 77, and 78 (C25). In an exciting instrumental means of minimizing polyatomic isobar interferences, Bradshaw and co-investigators have described the first coupling of an ICP ion source with a double focusing,

ratio data (flat-topped peaks are obtained) and improved detection limits (better ion transmission and lower background intensity) when operating in a low-resolution operating mode. Fundamental information on polyatomic ion occurrence/ distribution and ICPMS interface dynamics may also be expected from this new instrument design. Calibration and uantitation studies persist and should be of interest to mostyCPMS users, particularly the newly initiated. Doherty (C27) discusses the use of internal standards to relate observed determinate errors to analyte mass, the relationship of which is then used to correct for o erational variations occurring durin the analysis of geologi materials for rare-earth elements (RSE). The use of internal standards was also investigated for correction of matrix-induced effects and improvement of measurement precision (‘228). Multivariate caliiiration procedures (multiple regression analysis and principal components regression) were utilized in another study to extract analyte concentration data in the resence of isobaric olyatomic ion interferences (C29). External calibration !.e., simple use of standard solutions) was also demonstrated to be quite effective at sub- pm levels of analytes in biolo ical materials; internal stanxardization using the 40Ar2+pea[ was also utilized in this work (C30). Also of interest in regard to calibration studies is a report on the stabilit of low-concentration standard solutions-as used by practitioners ( ~ 3 1 ) . most The use of negative ion operation in ICPMS was originally a high1 held potential that has not, as yet, materialized. Fulfordlsuggests that the negative ions observed in ICPMS are not inherent in the plasma but rather result from electron ca ture or other reactions downstream of the expansion region (&2). Nonetheless, two studies examined the possibilities of negative ion detection in ICPMS (C33, C34). Other than application to halogens, little use is apparent for negative ion detection, however. In other fundamental studies of note, the noise power spectra of ICPMS and concurrent and separated ICP optical emission signals were determined, resulting in observed differences between the ICPMS and separated ICP-OES noise power spectra (C35). These differences were attributed to gas dynamic effects at the mass spectrometer interface; the noise was rimary l/f noise in this case. Background signals in I C P h S were examined in another study, using a noncommercial instrument (C36). The ion lens assembly of this instrument utilized a conelike optical baffle. Increasing background levels with increasing lens voltages implicated a ion lens disch e as a possible explanation for the effect. An increase of b x g r o u n d levels with a ion deflector placed immediate1 prior to the ion detector also indicated that backgroundcan be caused by ion collisions within the mass spectrometer a paratus. In a stud of plasma potential effects using a 4O-M& ICP system ( C 3 8 , differences in ion kinetic energies between analyte and polyatomic ions were apparently observable. In an effort to reduce gas and power requirements, the feasibility of em loying a low-flow torch was investigated for ICPMS (C38). #h e torch described operated at a flow of -2 L/min of Ar. In a final comment on fundamental ICPMS studies, a movement toward dry plasmas and dry plasma sampling is

J

IEPMS

306R


apparent in the ICPMS community. This is due to the ob-

mous problems associated with solution introduction, copious

amounts of H+ and O+ in the ion beams, hydride and hydroxide peaks, and consumption of RF power in the heating, phase change, and dissociation of water. Two studies of the effect of water on ICP characteristics and their influence in ICPMS are available (C39,C40). Complete delineation of the role and effect of H 2 0 in ICPMS ion extraction still eludes investigators, however. Sample Introduction Alternatives and Chromatographic Coupling. Viable alternatives to conventional solution nebulization in ICPMS continue to be examined for improved detection capability, freedom from problematic interferences, or relief from sample dissolution rigors (includin contamination). Electrothermal vaporization was employecfby several groups (C4144.9, and considering its ease of use with ICPMS and its considerable improvement in detection limits (femtogram levels in recent unpublished studies), ita more frequent use and optimization for ICPMS sample introduction is ensured in the future. Laser ablation was also studied (C46C49);its adoption and use by more and more ICPMS users indicate that a “critical mass” of users will soon exist, hopefully leading to real improvements in sample transport and quantitation knowledge. Arrowsmith discusses factors involved in ablation cell design and sample entrainment and transport effects using Mo metal as a test sample (C46). Hager empirically determined relative elemental response factors for metallic samples and verified a proposed metal experimentally (C48). Differences in response factors were observed between free-running and Q-switched laser modes of o eration in this study and were attributed to higher local sampg temperatures and more uniform response (vaporization/ionization dependent) with the latter mode compared to the former. A ruby laser was used in the application of laser ablation techni ues to the ICPMS analysis of geological samples (C47),provi%ng detection limits of 0.02-0.9 ppm (solid sample basis) for REE, Th, and U in rocks. Hydride generation was effectively used for Pb (C50) and Se (C51), while another vapor eneration technique was used for Os isotope determination %yICPMS (C52). Slurry sam le introduction, as applied to silicate rocks (C24) and coal (82.31, was also examined; the encouraging results obtained indicate promise for this approach as a expedient method of ICPMS analysis. The application of chromatographic techniques to ICPMS sample introduction offers interestin possibilities for speciation analysis and other environmentaf or biological problems. Reverse-phase liquid chromatography was used to separate and determine inorganic phosphates and nucleotides with detection limits of 0.4-4 ng of P, and sulfates and amino acids with S detection limits of 7 ng ((253). Chromato raphic techniques were also used to remove metal oxide inte erences from Ti and Mo on Cu, Zn, and Cd analytes (C54). The ability of chromatographic ICPMS techniques to provide speciation information was demonstrated in several re orts, including those applied to As (C55-C57), Hg (C58),a n I S n (C59). The application of the ICPMS technique as a powerful, but expensive, multielement detector forxhromatography has not as yet been demonstrated by real-sample application, however. Alternative Plasmas and Ion Sources. Microwave plasma sources using both Ar (C60,C61) and He (C62, C63) have been evaluated for use with MS detection. Developmental problems a He ICP source for ICPMS were also examined (C64),while a general review on mixed-gas and molecular gas plasmas was also made available (C65). Wides read adoption of these alternative plasma ion sources depen on resolution of sample introduction and plasma generation and stability problems, however. Applications. Reports of ICPMS applications doubled compared to the 1985-1987 review period, with numerous analytical exploits in the geological, environmental, biolo ical-clinical, metallurgical, food, and nuclear fields being fescribed. It is clear that ICPMS is making significant anal@ical impacts and finding enthusiastic reception in all a plications requiring trace multielement determinations. Tks section and an accompanying tabulation document these ICPMS application developments. A number of ICPMS a plication reviews now exist, the most notable of which is t f e Applications of Inductively Coupled Plasma Mass Spectrometry book edited by the late A. R. Date and A. L. Gray (AB). In this text, chapters on geological,water, isotope ratio, isotope

B

Bs


tracers, food science, petroleum, environmental, and metallurgical applications are deacribed. "his book provides a useful starting point for ICPMS novices and provides numerous a plication references (up to 1987-1988). for others. The c apters on geological, isotope ratio, and isotope tracer applications are articularly worthwhile. In literature reviews of ICPMS apppications,Riddle and co-workers review the use of the technique for rock analysis (C66) while Hutton reviews applications to water and envlronmental analysis ((267). The growing impact and value of ICPMS in the nutrition/metabolism/biomedid field are also reflected in several reviews on this subject (CSB-CSS). The importance and rapid acceptance of the ICPMS technique is reflected by its growing use in the certification of reference materials and the increasing ICPMS data found in round-robin data compilations. The research group at the National Research Council of Canada has been especially active in this area, with reference material characterization reports on marine sediments (C70),river and seawater (C71, C72), and marine biolo ical tissues (C73-C76). Other groups have also been usin I8PMS for analysis of the latter sample types (C77, C78). %ther investigators have used ICPMS for characterization of geological standards (C66, C79). The suitability of a plasma protein solution (albumin) as a biological trace element reference material was also investigated by using ICPMS (CBO),along with several other techniques for com arison (ICP-AES, AAS). Several of these reports involvef u s e of novel techniques, includin on-line preconcentration (C71),gas chromatography of CfI Hg (C74), flow injection (C75),and liquid chromatography (C76, C77). Isotope dilution techniques were utilized in many of these studies, illustrating the wider use of this definitive quantitation technique, as made possible by ICPMS. The application of ICPMS to stable isotope tracer studies for nutritional and biomedical purposes has been promoted bv Janehorbani and co-workers. In addition to fundamental -- w studies involving instrument parameter optimization o timization (C81), (C811, isoto e ratio a lications involving %M (C82) 7'Se/RSe/@Se@83), 57Fe/S8Fe (CB4, :%kp%r/8i%r (C86j in ingestion adsorption and other clinical studies have been s group also reported the isolation and ICPMS reported. determination of trimethylselenonium ion in human urine (C87),using precipitation, anion-exchange, and thermal decom osition preparation techniques. Other groups reported simirar applications, includin iron absorption during regnancy (using MFe 67Fe/6BF$ Cbk?),P b isotope ratios in &ood (C89, C90), and t e use of Cr as an erythrocyte label (C91). The use of ICPMS for radionuclide determinations is, as yet, a largely unrecognized capability, in spite of several cursory reports using ICPMS for this ur ose (C92497). With the low detection limits (fg) afforgdy! ETV-ICPMS techniques, radionuclides with half-lives greater than 10L106 years can likely be determined more rapidly, sensitively, and cost effectively than conventionaldecay counting techniques. Most a plications in this area have focused on nuclides with long haklives, including q c (C92,CM), '29 (C93),W p (C95, C96), and '?Pu =Pu (C97). In a different radionuclear aplication, ICP S was used to determine the half-life of '@'Re Ey determination of the ,!?-decay daughter '@'Osproduct from an initial1 Os-free Re sample (C98). The redetermined half-life vdue wm used to reevaluate the geochronology of iron meteorites and chondrites. Numerous other ICPMS were reported but cannot be reviewed in exhaustive detail here. Rather, many of these applications are cited in Table I, with available information on analyte elements/ratios and novel aspects of the applications. The widespread use and application of ICPMS is obvious from this tabulation. 2. Glow-DischargeMass Spectrometry. Glow discharge ion sources are receiving renewed attention for both organic and atomic MS applications. Current glow discharge technolog is being developed primarily for bulk solids analysis a plication, for which most promise exists. Perha s due to t i e immediate and overwhelming success of ICjMS, the growth of GDMS has been com aratively restrained. Other mitigating factors in this regar: have included the high instrument cost, relatively modest research interest, and the usual roblems accompan in direct solids analysis (i.e., suitabity and availability ofrekrence materials, homogeneity concerns, sample configuration requirements, etc.). The

1

-u

Ti,

h

d

former constraint has been rectified somewhat within the past year with the commercial introduction of several lower-cost, quadrupole-baaed GDMS instruments. Research participation by new academic and industrial groups has also increased recently. Thus, the future now appears brighter for GDMS techniques. Reviews and Assessments. Several new reviews of GDMS technology and virtues have been published since the ast review. Harrison, a primary advocate and pioneer in GD S , published two in-depth reviews on the sub'ect (C142, C143). Other reviews also exist (c144-C148), including reviews focusing on both high-resolution (magnetic sector) GDMS ((71444146) and low-resolution (C147) instruments and applications. One review focused on the use of RF glow discharges (C148). Fundamental Studies. Quantitation difficulties inherent in any solids anal sis techniques also manifest themselves in GDMS and have geen the subject of several reports. Huneke reports that excellent precision at concentrationsof a few ppb is possible but that the obtainable accuracy is highly variable (10-300%) and dependent on the selection and quality of chosen reference standards (C149). Sanderson also addresses aspects of GDMS quantitation (C150)and illustrates problems and solutions with various examples. Relative independence of GDMS from matrix effects is claimed in another report, where relative sensitivity factors (RSFs) were determined for 17 elements in six sample matrices; the determined RSFs varied by approximately an order of magnitude with RSDs of up to 34% (C151). Parameters affecting GDMS ion signals were considered by Harrison and co-workers; critical factors were identified as electrode position within the source, plasma conditions and composition (presence of getter agents), and degree of sputtering (C152). Methods for eliminating problematic molecular ion interferences in GDMS were also addressed in a recent investi ation (C153). In this study, incorporation of a collision ceyl between the GD ion source and the mass filter was effected, yieldin spectra free from certain polyatomic interferences with on y marginal decreases in analyte ion signal intensity. The conventional dc glow discharge source is not conductive to the analysis of nonconducting samples, and therefore the development of an RFpowered GD source is critical to the future success of the techni ue. Such development efforts were reported by one group TC154) and applied to both conducting and nonconducting samples. Applications. Utilitarian applications of GDMS have surfaced more frequently in the past 2 years, and various comparative studies including GDMS have been ublished. Two reports were published that utilized G D d S for the characterization of high urity A1 (C155,C156);comparisons with other techniques (IRAA, RNAA, others) were included. The analytical characterization of refractory metals was reviewed by Ortner et al. (C157)and included GDMS analysis considerations. The utilization of GDMS for determination of a-emitters (U, Th) in hi h-purity Al, Pb, and Cu was also discussed recently ( ~ 1 % ) . p lication examples using a newly commercialized quadrupole 8DMS instrument are available in a report b Taylor and Dulak (C159);detection limits of approximate& 100 ppb were determined, usin analog counting procedures. Comparison of GDMS with S&S for surface analysis and depth profilin applications was popular, with several reports in this area ecoming available (C1604163). One advantage of GDMS over SIMS is its ability to obtain reasonable accuracy (where the latter technique has a notoriously dismal record); the ability of GDMS to provide data within &30% relative accuracy at ppb concentration levels is generally superior to conventional SIMS efforts (C160, C163). The ability of GDMS to rovide depth profiling information, a prime application of IMS,has been investigated with both encouraging (C162) and disappointing results

h

f

R

%

8

(C161).

This review period thus ends with GDMS at a critical juncture. In this reviewer's opinion, GDMS has yet to establish a firm user foundation in analytical chemistry. Much of the literature in existence today results from efforts of relatively few research groups or manufacturer application laboratories. There are enerally more scientists reviewing GDMS than there are inaependent workers using, applying, and reporting their research and application results. The availability of less complex, lower cost instrumentation ANALYTICAL CHEMISTRY, VOL. 62, NO. 12, JUNE 15, 1990

307R


Table I. Selected Applications of ICPMS' application, sample type geological geol ref matl, feldspar separates rocks, soils, sediments iron ores mineral concentrates coal tourmalines silicate rocks rocks rocks ores marine sediments geol ref materials environmental water samples spring water urban particulates (NBS 1648) seawater plants waters, sed, tissues, fly ash membrane filters, workplace environment granitic ground waters water reference stds seawater biological, clinical rat liver, serum urine pig kidney protein, urine, bovine liver human serum, blood human liver, kidney marine tissues human plasma, urine urine tuna, contact lens solns marine tissues marine tissues dogfish tissue lobster tissue rat tissues plasma, blood, urine iron absorption plasma, urine urine blood, teeth, paint crabmeat kidney tissues foods milk fruit juices green vegetables food, general wine, milk metallurgy gold steels alloy steels Hf, Zr alloys Mo Mn ores

AI radionuclear soils soils, sediments miscellaneous ultrapure acids, reagents methamphetamine, -chloride semiconductor matls Cu foils, ion implant. math crude oil products

analyte, isotope, ratio determined

novel aspects of application

ref

REE Au, Pt, Pd numerous Pb isotope ratios numerous Th, U REE Pt, Pd, Ir, Ru T1 Os ratios 16 elements REE

direct soln aapir, preconcn used fire-assay, acid decomp sample prep polyatamic interfer considered ETV used, comp w/TIMS values slurry nebulization fusion fluxing of sample slurry nebuilization ETV introduction used ETV introduction used Os04 vapor generation used aAr2+ used as int std comp w/TIMS data

Cloo, c99 ClOl c102 (2103 C23, C104 C105 C24 C41 c43 C52 C70 c79

numerous W, Mo C1, Br, I Au platinum group metals Sn numerous

precon on activ charcoal various sample prep proc used preconcn, memory problems addressed ETV introduction used comp w/GFAAS comp w/other tech

C106-ClO8 c109 CllO Clll c112 C113 C114

numerous Mn, Co, Ni, Cu, Pb, U; Mn, Mo, Cd Ni, Cu, Zn, Mo, Cd, Pb, U

comp w/AAS, AFS, ICP-OES on-line preconcn employed 50-fold preconcn, ID used

c10 C71 C72

comp w/delayed neutron assay speciation study w/HPLC use multi-lab comparison

C116 C117 C118 c119 c120 C30 c44 c55, c57 C58 c73 c75, c74 C76, C77 C78 C82 C83 C84, C85, C88 C86

30 elems

C115

U Cd numerous Fe, Co, Cu, Zn, Rb, Mo, Cs numerous numerous Te As species Hg species 13 elems, incl Cr, Fe, As, Cd, Hg Hg As 16 elems, incl Cr, Fe, As, Se, Sn, Hg 26Mg/24Mg,%Mg/%Mg 02Se/71Se,I4SelnSe 68Fe/b7Fe I9Br/ OIBr Se Pb ratios Cd, As

microwave digestion, aAr2+ int std Te antitumor cmpd traced, ETV use HPLC sepn of As species HPLC sepn of Hg species ID, FI used speciation using HPLC C1 interfer corss DL 180) getedion possibilities (&).Energy range and accelerator types are considered as application-dependent Henning reviews the use parameters in another review (H4). of AMs for long nuclear lifetime measurements, solar neutrino experiments, and the detection of 41Cain terrestrial materials (H5).Ast reviews the use of charge stripping reactions of high-energy ions for mass spectrometry, particularly AMS (H6). Finally, Sellschop provides an interesting perspective on AMS progress in a conference summary paper for the above-mentioned AMS symposium (H7). Approximately 30 A M s facilities exist worldwide. Of these, most laboratories employ tandem accelerators that initially

cheolo!r

4,

x


313R


require negative ion introduction and result in various electron-stripped, multiply ch ed positive ions for further mass anal sis. Man of the AI% facilities are dedicated to only or a few radioisotope analysis ap lications. one &pically A proximately 12 AMS facilities exist in the U.8; Woelfli ta!ulatea relevant information on the AMs facilities as of 1987 (H2). Many of these facilities have also published details of their AMS confi urations and characteristics-usually with respect to speci ic isotope determination capabilities (H8H26). One of the primary features of AMs is the ability to analyze extremely small samples, enabling microscopic or essentially nondestructive analysis. This requires careful sample preparation and preconcentration, however, and these subjects were the focus of several publications over the review period. Slota et al. describe a reduction procedure for pre graphite tar ets for 14C AMS measurements treatment o carbonate-containing sam les for this same measurement is described by Lowe an co-workers usiqg microwave oven procedures (H28); reduced contamination from modem carbon and increased convenience were claimed by using this procedure. Steinhof and co-workers describe procedures to enrich 41Cacontents of natural Sam les using electromagnetic isotope enrichment techniques &29); enrichments of 8-20-fold were achieved prior to AMS measurements. Iodine and chlorine are extracted and separated from a U ore matrix in a procedure described by Roman and Fabryka-Martin for and -1 determination by AMs (H30). Fusion and preci itation as AgCl was used by Kato et al. for separation of 38 1 from silicate rock samples (H31). Traditional radiochemical separation procedures, including ion exchan e solvent extraction, and precipitation methods, were descrikd by other workers for '"Be, =Al,-1, 41Ca,W n , M s (H32). In related topics, the and beNidetermination by A subject of laboratory and procedural contamination in 14C reparation procedures was addressed by several groups (H33, 34),who compared and assessed several preparation procedures for l'C countin by AMs. The development of a Be determination of '"Be has also been isotopic standard for described by Fasset and co-workers at NIST (H35). Hofmann and co-investi ators also describe preparation of a 'OBe standard for A h S calibration (H36). AMs technique development has slowed somewhat, but it is certainly not over. Kubik and co-investigators describe experiments using a gas-filled m et to resolve stable atomic isobar problems, using the pair as a dia nostic tool (H37). Improvement of 100-fold was observe{ compared to using a ionization detector alone. Hi h-energy ions from ion s uttered solids contribute to overall hckground in AMs; the cLaeteristics of the ion energy distribution resulting from Cs+ ion bombardment were evaluated by Kilius and coworkers in an attempt to reduce such back round in this Matteson et al. found it u s e d t o incorporate technique (H38). a high-resolution electrostatic analyzer as part of their AMS detection system and describe its ex loitation in an interesting These same workers describe the automated article (H39). operation of their AMs system, designed for trace analysis of electronic materials (H40). Automatic control of beam transport and mass discrimination hardware, in addition to selection of ion charge state, isotope species, and rejected molecular ions is described. Chen and co-workers describe the tential advantages of a minicyclotron accelerator-based AMPs ystem (H41) and also theoretical1 calculate particle acceptance conditions for this device ( 42). The practical analytical im etus for the development of AMs was the potential for 148-dating improvements. Extension of the traditional decay counting age limit of -5OOOO years and a decrease in the amount of carbonaceous material required for age dating were two of the hoped-for benefits to Although success in the be realized by AMs technolo former area has been mixed, YMS has definite1 rovided The improved l'C dating capability for small samples M s most interesting example of this new ca ability was the A 14C age dating of the purported b u r d c l o t h of Christ (the Shroud of Turin), by a consortium of A M s laboratories (H44, H45).Small patches (-40 mg) of this cloth were distributed to three AMs laboratories along with control samples of known age. Each laboratory subsampled its Shroud sample and determined the asaociated "C content and date. Excellent agreement was found between all laboratories; a determined

lk) P

f

B

A S

-%/%

&

d

H3).

314R

radioisotope 1 4 c

Shroud of Turin, cloth

tree cellulose ocean water marine organisms, shells, cores atmos methane misc archeol samples misc environ samples sediments, phosphate pellets SH atmos air soils nNa, 24Na activated sample 'OBe chondrites, meteorites


HA

*e1 "Ca

@Mn ID1

ref

application, sample type

m.s%t

8

fz

Table IV. Radioisotope Determinations by AMS

soils, sediments U, Th host rocks marine sediments chondrites, meteorites misc terrestrial samples U, Th host rocks marine sediments

H44,H45 H46,H62 H47-H49,H59-H61 H50,H51,H53,H58,H67 H52 H63 H64-H66 H76 H68 H77 H69 "70, H73,H74,H85 H75,H78 H79 H81 H70,"74, H85 H72 H79 H81

H71 H77

U ores soils meteorites bone

H83 H80

meteorite chondrites

H86 H70

U ores misc terrestrial samples

rainwater (post-Chernobyl)

H71 H72 H82 H84 H87

groundwater

Detroleum

cloth date of 1260-1390 A.D., indicated that the Shroud could not, in fact, be the burial cloth. While this exam le has been the most famous AMS application, numerous ot\er applications also exist. Correlation of radial tree cellulose samples analyzed for 14C with previously determined or calculated atmospheric 14C02was shown for the 1962-1964 period, indicating that photos thetic records of bomb-produced radiocarbon are possibg(H46). Determination of 14Cin ocean water samples was also performed using AMs, significantly decreasing the amount of seawater required for proceasing and pre aration of 14Csamples (H47-H49). The use of marine sheEs for 14C determination was also shown to be a useful chronometry tool (H50, H51). Other applications for 14C measurement using AMs inand dee -sea cores (H53). cluded atmospheric methane (H52) Several reviews of AMS '42 capabilities analimitations exist this new and should be consulted for consideration in ut age-dating method (H54-H56). Problems associa with the AMS 14Cmethod do exist and include fractionation effects (H57) and contamination with modern carbon duri sample pre aration and manipulation (H33, H34, H43). '%e latter protlem now ap ears to be the limiting factor in the AMs M s facilities extension of 14Cf e a y dating age. Many of the A are either devoted for 'Y! determination or include this isotope as one of 2-3 radioisotope ca abilities. Numerous applications of AMs to the analysis of in archeological, environmental, and geological sam les are presented in the s y m osium proceedings reference! above; several of these appications are tabulated in Table IV. Application of AMS to other radioisotopes w&s also popular, as few (if any) alternative techniques are available for these long-lived nuclides. A list of radioisotopes and ap lications for this use of AMS is given in Table Iv;this list is 8ustrative only and not complete (see AMs symposium roceeding, mentioned above, for additional applications). &tension of A M s to other analytes is also reported for example, %i (Ha), 'Be (H89), 3H (HN), 3He (H91), and &Pb (H92); these studies indicate a growing usefulness for the AMS technique. Applications of A M s to the more traditional trace-element analysis roblems faced by many analytical chemists are being reportexwith increasing frequency. Anthony and Donahue

9

l'8


apply the techni ue to the analysis of semicondudor samples, for example (2393).Various impurities (B, Cr,P, Ge,As,Sb, and Au) were measured after ion source and sample holder modifications to reduce contamination effects. Sensitivities of 0.1 ppb (atomic) were achieved; 1ppt (atomic) sensitivity was projected predicated on further improvements. Comarison of results with SIMS indicated much less complex gackgrounds and correspondingly lower detection limits. Rasmussen and co-workers determined the contents of W, Re, Os, Ir, Pt, and Au in iron meteorites using AMS (H941,although some debate over the validit of the W and Re values so determined was voiced (H95, H%f Determination of these elements at the low ppm level was demonstrated with a precision of *7-10%; detection limits below the pg/g range were estimated. Ten and co-workers also determined Os and Re ratios usin AM{ (H97).The difference in ne ative ion production eftciency between Os and Re allowe determination of the former a t m l z 187 with minimal interference by the latter element. The Re content and isotope ratio were then determined by using.Re0- ions a t m l z 201 and 203, instead of the monatomic ions a t m l z 185 and 187. These applications are among the first uses of AMS to nonradioisotope determinations. The current constraints in AMS use for such traditional analysis problems include contamination and memory effects (primarily from the sputter sample source), matrix effects, and system availability. The former problems are all too familiar to $e analytical chemist; perhaps increased interest and participatlon by this grou wdl nurture further application of AMS techniques for traitional traceelement analysis needs.

B

I. SECONDARY ION MASS SPECTROMETRY Secondary ions result from the ion or neutral bombardment of material surfaces. The mass spectrometric detection and identification of these sputtered secondary ions constitutes the field of secondary ion mass spectrometry (SIMS), one of today’s fastest growing and most widely applied analytical techniques. Atomic, molecular, or cluster ions can be found in most second ion spectra; this distribution has been both a plague and x o o n for the SIMS technique. Originally deemed a severe detriment to qualitative or quantitative analysis by SIMS, the abundance of molecular ions in such spectra ultimately led to the turning of a negative attribute into a positive one with the development of static or molecular SIMS. This use of SIMS (for analysis of nonvolatile, highmolecular-weight molecules) has expanded rapidly in the last several years with its adoption by the organic mass spectrometry community. Consistent with the aim of this review, however, the focus of this section.is ?n the use of SIMS for elemental and isotopic characterization of materials. The nature of the secondary ion formation process is such that it is primarily a surface analysis technique. Nonetheless, increasing use of SIMS for bulk and microspatial analysis is evident in the publications of the past 2 years; this application and use is featured in this review section. A particular note on the SIMS literature is appropriate he’e. The SIMS technique is immensely popular and useful in certain fields (e.g., the microelectronics and materials analysis disciplines). Its use in these areas is so commonplace that the inclusion of the SIMS acronym or phase is included in hundreds of literature titles, abstracts, or keywords even though no particular emphasis on the use of development of the technique is included in the published work. It is estimated that of the total literature search “hits” received in preparation for this fundamental review, approximately 50% of them (1200-1300) resulted from the SIMS topic. Due to the number of literature citations received and the timelspace constraints for this review, this treatment of atomic SIMS will necessarily be more selective and subjective than the other topics. A separate, s ecific review on this topic is clearly justified (or alternativeyy, its inclusion in a Surface Analysis review); hopefully this can be arranged in future issues of this journal. A excellent syno sis of current SIMS activity is best achieved via purus8of the proceedings of the 6th International Conference on Secondary Ion Mass Spectrometry (SIMS VI), a len h (1O00+ p) volume containing 3-6-page descriptions of SGJrelated research (A4).As for previously cited roceedin s volumes, a collective reference to this work is maze here. h s o of relevance here is the fact that the 7th conference on this topic was held in late 1989 and it is pre-

sumed that the proceedings of this conference will be available sometime in 1990. Also made available in 1989 was a new book entitled Secondary Zon Mass Spectrometry, A Practical Handbook for De th Profiling and Bulk Zm urity Analysis (11);the book incides major sections on an ysis conditions, profiling approaches and problems, quantification, and applications, with a articular emphasis on provision of pragmatic, little-publisked information and data acquired by the authors over years of SIMS analysis use. Literature reviews of the SIMS technique and related phenomena abound. Adams and co-workers review the subject with particular emphasis on quantitative capabilities and depth-profiling applications (12). The rapid1 growing field of ion microscopy was reviewed by Bernius an Morrison (13), with comparison of both scannin and stigmatic type microscope instruments being discusse (see also comments, 14,15). Ion imaging fundamentals are also summarized by Slodzian (16).S utter ionization processes are reviewed by Sroubek and inckde discussion of tunneling and bondbreaking models (17). Fundamental aspects of SIMS are rewewed by several authors (1419)and include treatment of sputter’ processes and mechanisms as well as spatial and depth reso ution constraints. Grasserbauer provides an informative applications review for SIMS, including examples of ppb level analysis (110).Other general reviews of the SIMS technique are also available (111). Quantitation difficulties remain as the primary technical impediment to SIMS use and application, and consequently much fundamental and empirical research is directed toward resolving these problems. The problems inherent in SIMS quantitation have been articulated in several publications (12, 112-114). Matrix effects on ion production and relative ion yield are problematic; Adams discusses such effects on the uantification of major and trace elements in brass (115,116). 8aluska et al. notes great differences in relative ion yields of Al,Ga As samples using three different SIMS instruments with &$ primary ion bombardment (117);the noted differences were attributed to the different surface oxygen concentrations produced by each instrument, in contrast to the essentially similar sputtering yields. With freeze-dried cellular samples, however, ion yield variation with cell location was insignificant when compared using external standards, ion implantation, or electron-probe comparison analysis aproaches (118). Ion yields and detection limits were examined Ey using SIMS and highly doped InP samples (119).In this case certain molecular ions were found to give better ion yields and lower detection limits than their atomic ions (e. GePapproximately 50-fold better than Ge). Such ion yielrkffects apparently manifest themselves with isotopes as well. For example, Gnaser and Hutcheon report preferential ejection of light isotopes relative to heavier ones in the initial stages of ion sputtering (120). The effect decreased to a steady-state value after an initial s uttering period; compared to the steady-state value, early%eam enrichment factors of 1.05-1.6 were obtained for Ti and Li isotopes (Ga and Mo isotopes exhibited the same effect as well). In addition to these matrix interferences,Williams and co-workers observed recision and accuracy degradation due to simple sample misa rignment and consequent analytelreference ion discrimination (121). The availability of standard materials with which to compare secondary ion yields and calculate response factors also poses a limitation in SIMS quantitation. The use of ion implantation techniques to develop useful SIMS standards with appropriate lateral and depth resolution remains an area of acute interest. Gnaser describes in situ ion implantation quantification for determination of interfacial oxygen concentrations (122). Also described in this study was the use of deuterium ion implantation for hydrogen distribution determination. W h n and co-workers extended this rare isotope implantation apBroach to use of other low-abundance isotopes, includin 13C, N, l80, %i, %, and “Fe (123). The dependence ofpositive and negative ion yields on ionization potential and electron affinity, respectively, were examined by using ion implantation techniques (45 elements implanted into HgCdTe, CdTe); ion yield models were general1 (but not without exception) verified by using the obtainei data and inte retations (124,125).A unique hollow cathode ion source wasTescribed by Streit and Williams for use with the Cameca ion microprobe to facilitate the use of ion implantation techniques for most elements in the periodic table (126).

s

d

d

1


3i5R


Interlaboratory com arisons and round-robin anal sis studies have been coniucted to assimilate universal J S F information and establish interlaboratory analysis techni ues. Riedel et al. describe the cross calibration of various SIMS instruments using two metallic glass and several semiconductor samples as reference materials (127).A compilation of RSF data for 12 elements was produced and is available from this stud ;continued expansion and use of these data are envisione for semiquantitative analysis. In another round-robin study, RSDs of 10-12% and relative errors

Atomic absorption, atomic emission, and flame emission spectrometry

Recommend Documents