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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 third fundamental review on the subject of atomic mass spectrometry, an analytical discipline enjoying renewed scientific vigor and consequence publication activity. No longer just a mainstay technique of organic analysis, mass spectrometry is increasingly being rediscovered as the method of choice in many inorganic analysis situations. The rising popularity of the mass spectrometric a proach is certainly coincident with, if not actually fueled \y , the tremendous commercial and technical success of the inductively coupled plasma mass spectrometry (ICPMS) technique. This technique, more than any other, has put atomic mass spectrometry back in the analytical spotlight. It has truly become a techni ue for the masses (pun intended); a noticeable increase in IC%/MS publications has been observed compared to the previous reviews in thisseries (I,2). Other techni ues, notably glow d i s c h g e mass spectrometry (GDMS), accderator mass 0 erated for the U.S. Department o f Ener by Battelle M e m orial Pnstitute under Contract D E - A C 0 6 - 7 6 R 8 1830. 320 R
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spectrometry (AMs), and resonance ionization mass spectrometry (RIMS) have received increasing developmental and applications interest in the literature of the last 2 years. More established atomic MS techniques like thermal ionization and stable isotope ratio mass spectrometry (TIMS, SIRMS, respectively) have found continued utility in geochemistry, radiochemistry, and biochemistry investigations. Surface analysts continue to re1 almost exclusively on secondary ion mass spectrometry (SILS) for surficial and depth-resolved compositional characterization. Interest in laser ionization mass spectrometry (LIMS),outside of RIMS-based methods, seems to have ebbed somewhat in the reviewed literature. Spark source mass spectrometry (SSMS), the paternal multielement mass spectrometric technique, refuses to yield completely to the newer techniques and was still in use in a surprising number of ublications surveyed for this review. Other techniques, incyuding sputtered neutrals mass spectrometry (SNMS), photon burst mass spectrometry (PBMS), and neutron activation mass spectrometry (NAMS) offer tantalizing new analytical prospects for difficult analytical problems and are on the horizon. Recent studies using tools @ 1992 American
Chemical Society
ATOMIC MASS SPECTROMETRY David W. Kappenaal is a Staff Scientist and Technical Group Leader with Batteile Memorial Institute, research contractor for the US DOE’SPacific Northwest Laboratory in Richland, Washington. After obtaining a B.S. degee from Southwest Missouri State University in 1974, he received his Ph.D. from the University of Missouri (Columbia) in 1978. He has also held research staff positions at the University of Kentucky and The University of Texas at Austin. At PNL, he is currently in charge of a 12-member research, development, and applications group s p a ciaiizing in advanced inorganic analysis methods where ICPMS. thermal ionization. and gas ratio mass spectrometry techniques are employed. Current research interests include the development of advanced laser ablation techniques for soiMs analysis, and the incorporation of both traditional (magnetic sector) and nontraditional (ion trapping) mass spectrometry approaches to the continued development of ICPMS. Dr. Koppenaai is a member of the American Society for Mass Spectrometry, Society for Applied Spectroscopy, and the American Chemical Society.
such as fast atom bombardment (FAB),ion trap and ion cyclotron techniques, graphite furnace ionization, plasma and ’ particle desorption, and even flame ionization serve to indicate the potential expansion of the field and the versatility of the scientist in employing mass spectrometry as an elemental and isotopic analysis method. This review once again attempts to summarize and spotlight both the unique developments and the practical applicationsof mass spectrometry for atomic and inorganic materials analyses. Atomic mass spectrometry is defined as the mass spectrometric measurement of atomic ions for either concentration or isotope abundance determinations. Molecular ions are actually used for quantitation in certain applications of the reviewed techniques, but elemental or isotopic data is the information sought for, and relief from the strict definition above is granted in these cases. The atomic mass spectrometry term is preferred by this reviewer over more generic labels like inorganic mass spectrometry or solids mass spectrometry, both terms which increasingly overlap with subjects not germaine to trace analytical chemistry and lead to confusion with and or omission of other legitimate mass spectrometry topics. urthermore, the advocated terminology is consistent with other popular trace element analysis techniques, including atomic absorption, atomic fluorescence, and atomic emission. As in the past reviews, the basis of the present review is a computerized literature search using literature titles, abstracts, and keywords from the Chemical Abstracts data base as source material. The time period from late 1989 to late 1991is covered. Approximately 4000 citations were reviewed for this period, an increase of almost 75% over the 1990 Atomic Mass Spectrometry review! The volume of material published necessitates a very judicious and critical selection of covered works, and advance apologies are given to those whose investigations are not included. In general, only widely available peer-reviewed journal citations are referenced; government reports, patent references, and foreign journal references are usually not cited. However, in certain fields where foreignjournal citations represent a major or important contribution to the body of the literature, they are referenced with an accompanying Chemical Abstracts accession number for the reader’s use. This reviewer regards both technique development and its ap lication to real-world analytical problems as equally valid inzicators of scientific interest in a particular technique. Consequently, applications are discussed on an equal footing with the more glamorous developmental studies. In most sections, particularly interesting or innovative applications are discussed within the text while more pragmatic applications are tabulated for rapid perusal and survey of the technique’s range of utility. The reader is also directed to the alternate-year application reviews issue of this journal for specific information relative to a certain sample or material type. For the trace element analyst, this review should be consulted in conjunction with the “Emission Spectrometry” and “Atomic Absorption, Atomic Emission, and Flame Emission Spectrometry” reviews also found in this issue of the journal. For the mass spectrometrist, this review and the “Mass-
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Spectrometry” review should encompass the entire mass spectrometry field fairly completely. A. REVIEWS, BOOKS,AND COMPARATIVE STUDIES The continuing interest in atomic mass spectrometry is reflected in the number of new reviews, books, and comparative studies published in the last 2 years. The Atomic Spectrometry Updates on Inorganic Mass Spectrometry and X-ray Fluorescence are excellent review sources very complementary to this review ( A I , A2). These reviews continue to expand and offer an excellent annual snapshot of activity in the atomic mass spectrometry field. These reviews include the enormous undertaking of reviewing not only the published literature, but also conference reports and abstracts. The University of Belgium group continues their prolific contributions to the atomic mass spectrometry field (as will be indicated throughout the remainder of this review). Reviews by this group include one on the applications of mass spectrometry to high-purity solids analysis (A3) and fundamental discussions on aspects of ion formation and production in plasma ion sources for mass spectrometry (A4, A5). The latter review discusses in particular depth the common physical aspects of many of the popular ion sources, including ICPMS, GDMS, LIMS, and SSMS (A5). Generic mechanisms of ion formation are also treated by Ramendik, in his quest for a general theory for elemental mass spectrometry methods (A6). Toelg reviews mass spectrometry methods as well as conventional optical techniques for increased detection power potential ( A n , while Houk and co-workers discuss new developments in ICP/MS and laser desorption techniques in a discussion on frontiers in elemental mass spectrometry (A8). A comprehensive review of mass spectrometry and its role for isotopic measurements in the nuclear industry was published (A9). De Galan, in a broad reflection on modern atomic spectrometry, acknowledges ICPMS as a “potential” contender for general utilization in elemental analysis (A10). Numerous investigations comparing/contrasting various atomic mass spectrometry techniques applied to specific problems were published during the review period. Several techniques (GDMS, SIMS, ICPMS, and SNMS) were evaluated for trace element determinations in refractory and hard metals ( A l l ) . Two comparative reports exist on the characterization of CdTe and related compounds; GDMS, SSMS, LIMS, and SIMS found utility in these investigations (A12, A13). Direct solids mass spectrometry techniques (GDMS, SSMS, SIMS) were compared with ICP optical and mass spectrometry methods using matrix separation techniques (A14). It was concluded that the latter techniques offered better accuracy and precision than the former methods, which suffered in the case of refractory metals analysis due to sample heterogeneity. The application of mass spectrometry for agricultural applications is addressed in an investigation by Ure and Bacon (A15);the use of SSMS, GDMS, and ICPMS is discussed in the analysis of soil samples. Recent developments in geochemical microanalysis, highlighting ICPMS and SIMS methods, have also been reviewed (A16). Finally, instrumental methods for analysis of petroleum-related materials, including SSMS, are discussed and reviewed in a recent review by Nadkarni (A17). The publication of several books relevant to this review subject took place during the review period. The latest in the series of proceedings of the Secondary Ion Mass Spectrometry Conference (SIMS VII) and the Fifth International Resonance Ionization Spectroscopy Symposium were published ( A D , A19, respectively). A new volume on the principles and applications of SIMS method also appeared (A20).Proceedings volumes from two plasma source mass spectrometry conferences appeared, the f i t from the Second Durham Conference on Plasma Source Mass Spectrometry ( A H ) and the other from the Third Surrey Conference on the same subject (A22). A new Handbook of Inductively Coupled Plasma Mass Spectrometry is also hot off the press; authored by Gray, Houk, and others, the book provides much practical information and documents many ICP/MS facts, “conventional wisdom” ti s, and operating hints for ICP MS users (A23). The seconcfrevisionof the ICP treatise In uctively Coupled Plasmas in Analytical Atomic Spectroscopy by Montaser and Golightly contains three revised and/or new chapters on , ICP MS status, fundamentals, and applications (A24). The stab e isotope geochemistry community pays tribute to one
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of its pioneers, Samuel Epstein, in a new volume on isotope geochemistry in geological investi ations (A25);emphasis is placed on thermal ionization and stable isotope ratio MS applications. B. SPARK SOURCE MASS SPECTROMETRY Spark source maas spectrometry (SSMS)continues to retain ita popularity (particularly in countries outside the US.)for isotopic and elemental com osition determination. Despite being over 30 years old at t is date, the technique was still the subject of several fundamental investigations in addition to a respectable number and breath of application reports. The fundamental physics of the high voltage spark process was investigated by several grou s in efforts to improve the quantitative ca ability of the SfMS technique. Ramendik and coworkers Rave advocated a generic approach to mass spectral analysis that depends on the derivation of fundamental physical princi les involved in ion formation; specific considerations usin 8SMS behavior are used as a basis for their theory (B1,B27. Their uasi-equilibrium approach was validated in a separate stuly that utilized four internal standard elements (without other reference standards) to improve analytical performance (B3). The dynamic ion processes within a s ark source were studied in relation to voltage oscillations Burin breakdown by Van Straaten and co-workers (B4);their stuiies demonstrated a possible cause for certain maas diecriminationeffects. Ionization m e c h a ” were also studied in both anode and cathode plasmas within the spark source (B5).This stud , which utilized liquid metal ion sources to examine plasma ehavior, includes some fascinating photomicro ra hs of emitter and cathode surfaces. Polymeric ions of t t e Erm Mp+have always been somewhat problematic in SSMS and this problem was addressed in several studies, as follows. The yield distribution of such ions was determined for 11elements in different matrices in one study (B6). A general distribution was generally followed for any ion M and polymer n, but dependences on the distribution were found to vary by matrix. In a related study, the formation of carbide, oxide, and other (hydride, hydroxide, halide, cyanide) ions were also studied for their mass spectral distribution behavior, with a general conclusion that a molecular ion maas spectra should be predetermined prior to any analysis for most matrix types (B7). The dependence of analyzer pressure on the formation of polynuclear metal ions was also examined and predidabl found to effect such ion distribution (B8). To prove that SZMS is not yet dead, new software programs continue to be developed in efforts to computerize the difficult job of SSMS photoplate data processin (B9). New and somewhat innovative applications of S S d S also found their way to print. Saito discusses the analysis of small (
