A ID-8IMS determination of U and double-quadrupole filter assembly was used by Laue and Wollnik to reduce the incidence of scattered ions on Faraday collector cups, resulting in a fold improvement in abunThe calibration of individual collector dance sensitivity D Sam le-preparation schemes for TIMS determinations eneraiy require andyte preconcentration or separation. Cleaner than conventionally obtained d and Sr ractions were obtained by using the described procedure. Direct filament-loading techniques for r! Precise determination of picogram quantities of REE was claimed in this work, in which careful monitoring and control of filament current and source ox en partial pressure was necessary for successful direct-loagg analyses.
Lowtemperature i. In another study, Chilipenko and Katruzov observed anomalous fractionation of LiI during TIMS analysis ;reliable measurements were found only after complete dehydration of Li salts on the filaments. Early eluant fractions exhibit a depleted fraction of 89Gawith a steady increase in this isotope throughout the elution. A materials balance for the light and heavy isotopes was in accordance with the isotopic Composition of the starting sample, illustrating a definite effect that is cause for concern when utilizing-ion-exchangeprocedures, even for relatively high mass analytes.
The commercial availability of a quadrupole TIMS instrument is of interest as initial capital and-o erating cost reductions would be ex ected.
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Featuring a small instrument package with [oth Faraday cup and pulse-counting detection for both positive and negative ions, this TIMS capability should provide access to users who cannot afford or do not need a high-performance system. This system has been applied to various analyte determinations in various sample matrices by Heumann and co-workers, including the measurement of Fe isotope ratios in water and biological samples and reference materials 0 2 3.
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Additional applications indicating the versatility and requirements of the TIMS technique include the determination of nuclear fuel burnup via monitoring of U, Pu, and Nd isotopes In this work, nanogram amounts of U and Pu were adsorbed onto small anion-exchange disks that are directly deposited on TIMS sample filaments. IDMS quantitation was used, with isotope ratio precisions of 0.
Absorption of Ca in premature infants was measured by using a dual tracer techni ue, relying on TIMS for isotope ratio determinations 0 3 0 , 8 3 1. The use of nonradioactive tracers to study Mg regulation in cells was also reported ;Mg stable isotopes were utilized to measure ion fluxes in barnacle muscle fibers in this study. Many of these applications are summarized in Table 11, along with the salient features of their application. As a concluding note of this section, information on the availability and composition of several new isotopic reference materials, primarily intended for use with TIMS instruments in the nuclear field, is available , These variations provide unique information regarding the biologic or geologic processes involved in the incorporation of these elements and the chemistry of their associated compounds.
Mass spectrometric techniques used for the determination of isotopic composition of these elements are popularly referred to as stable isotope ratio mass spectrometr SIRMS procedures and are heavily employed in clinical, giochemical, and geolo ical investigations. Its use in these fields is so commonpkace and the procedures of SIRMS so traditional that the oridinary use of SIRMS is transparent to computerized literature searches of the type employed for this rewew, since SIRMS keywords are often omitted in such publication abstracts.
A number of interesting ap licdtion studies are reported, however, in addition to new jevelopments in SIRMS sample-preparation methods. Fractionation effects are problematic in the preparation of samples for SIRMS due to the low mass and large isotope mass difference characteristics of these elements. Typical sample- reparation procedures have focused on the nonfractionatefgeneration of sim le ases i.
These pre aration procedures are typicall slow and labor intensive antrequire vacuum conversion andrmimipdation techniques that involve as much art as science. There is consequently much interest in the generation of new preparation techniques that offer rapidity, consisten and flexibility while retaining the isotopic integrity of the g m e n t of interest.
The grain size of the Zn was found to be less critical in this study, in contrast to other studies. Chinese investi ators also used this procedure with good results E2 , as did burner and Gailitus, who described a single-step variation of this technique for application to soil and other geological media E3.
In this latter work, both sample and Zn-shot are laced in a separated single-glass vessel, with cryogenic a n 8selective evaporation techniques being used to remove the HzO from the sample and react it with the reducing reagent. Automated systems for the preparation and collection of C02 samples were described by Brenninkmeijer E5,E6.
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Such techniques necessarily waste large amounts of sample, as it is necessary to continuously consume both sample and standard gases while only analyzing one. With this instrument, subnanomoleYevels of N2 are analyzed, and the performance of the instrument is appraised through analysis of reference samples, examination of precision limiting parameters, and evaluation of background and memory effects.
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An accompanying article by the same workers describes preparation procedures designed for the extraction and purification of subnanomole quantities of Nz E8. Emphasized in this work is the elimination of Nzblank contributions and other species CO, COz, CHI that cause interference at the m j z 28 and 29 peaks. Exam les using pro rammed pyrolysis techniques are also descriged. The adoption of these techniques is especially popular in the biomedical and clinical fields, where sample types vary widely and stable isotope tracer concentrationsare high, factors that are amenable to the versatility of this preparation technique and the acceptable lower isotope ratio precision obtainable.
Instrument configuration reports on the use of SIRMS with elemental analyzers E l l and gas chromatogra he E12,E13 are described and discussed with otentiapa lications. The extension, application, and evaluation of this technology to the geological field, where sam le volume and precision requirementsare more stringent, willte awaited for now, with interest.
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A review of applications of S1f;MS in pediatric pharmacology is also available E The ability to utilize lasers as "soft" ionization sources for molecular fragmentation is critical to the former a plication while the ability to provide in situ, ultratrace p gp, microelemental analysis at a spacial resolution a proaching a few micrometers is of obvious advantage in t i e latter application. Interest in LMMS techniques has been sufficient to encourage and support the commercial availability of at least three instruments. These instruments operate in several operational modes based on laser-sample-MS geometry: transmission modes, where a thin sample is located between the laser source and the MS detector; reflection modes, where the laser and MS detector are located on the same side of the sample; and a combination eometry mode, where either of the above modes are available.
Several reviews of LMMS have been published recently FI-F5 that will serve to introduce the capabilities and typical applications of the technique. Chapters in this text relevant to LMMS include those on laser-target interactions i.
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The primary analytical constraint associated with LMMS remains that of quantitation. The fundamental problem regarding quantitation difficulties is the relative paucity of basic information on energy absorption and ion formation processes. Consequently, this has been an area of active research and has been approached from both theoretical and practical viewpoints. Vertes and co-workers evaluated energy deposition processes in an effort to understand LMMS ionization mechanisms F6.
Shock wave, plasma ignition, and energy absorption mechanisms are ostulated, demonstrated, and used to account for observef spectral resulta and features. These same workers address conditions necessary and observed for microplasma formation in LMMS, using an adiabatic absor tion model to differentiate between laser desorption anllaser plasma ionization FT. Direct observation of ion yields was attempted by others in an effort to solve this fundamental part of the LMMS puzzle F8.
These workers used a fast-current robe and digital signal storage techni ues to monitor ion yielfs directly in the laser lasma and app ied their results to examination of ion yield ipendence on laser focus, among other parameters. Ion energy distributions were also studied in LMMS processes, and reports concerning instrumentation for such measurements were described F9 as well as a report in which ion energy distributions were found to change as a function of total ion production FIO.
Interion associations, as observed in individual pulse mass scans of CsI and Y Ba2Cu3O7superconductorsamples, were also examined in an effort to determine the statistical influence of association of one observed ion on another ion F Laser-induced electron avalanches in LMMS were observed in another study F12 and were postulated to be space-charge driven. In a more pragmatic study, Musselman and co-workers examined the effect of sample geometry on quantitation using RSFs F In this sim le but informative study, mass spectral data were acquirezunder identical system conditions using glass samples of the same nominal composition but different morphology thin films, glass spheres, and lass shards.
Best measurement figures of merit were obtained when analyzing unknowns using standards of similar geometry, and low ionization potential elements gave better results than high ionization potential elements.
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A number of research reports investigated the separation of laser ablation processes from laser ionization using postablation, secondary laser ionization techniques. Odom and Schueler applied this approach to the analysis of thin-film dielectrics, metallics, and semiconductor materials F14 and hosphosilicate glass F This approach is also advocated gy Becker and co-workers, who have applied the term SAL1 surface analysis by laser ionization to their work, where an intense UV laser beam is used to ionize laser-sputtered neutrals from sample surfaces F Instrumentation reports relevant to LMMS included the development and application of a laser microprobe-FTMS Fourier transform mass spectrometry instrument with extremely high mass-resolution capabilities F In another interesting and continuing development, retrofitting of old SSMS instruments with laser iolllzation sources was reported by several groups FF24 and assessed in re ard to ion yield characteristics F Advantages of the aser ionization source relative to the original s ark ion source were the ability to directly analyze nonconfuctors and the acquisition of more uniform RSFs.
In a report on sample preparation for LMMS, Fletcher described a technique for mounting samples on quartz fiber filters, citing advanta es of low contamination, low background high transparencyf and sample loading ease F Application of LMMS techniques was focused in two primary areas, namely, biological tissue analysis and particulate characterization. Microanalytical determination of A1 in biological tissues by LMMS was also undertaken by several groups; ap licatioy to rat vertebrae?
The identification of asbestos fibers in lung tissues and bronchial-alveolar fluids was also undertaken usin LMMS techniques by Adams and co-workers F These applications, ty ically utilizin. Particulate analysis using LMMS included environmental and industrial a lications. In another study with environmental implications, attempts at speciation of N in micrometer-size particles were undertaken using LMMS F By use of N cluster ions, the inorganic N composition of atmospheric aerosols and their environmental transformation was investigated in this work.
Particulate material in cathedral wall leachates was also studied by using LMMS techniques in conjunction with electron probe analysis methods F Differentiation between coprecipitated and adsorbed P b on calcite particles was also demonstrated by using LMMS approaches F Industrial LMMS applications were numerous and varied. Refractory materials F,gfass 45 , electronic materials F46 ,and superconductors F47 were analyzed or characterized with the aid of LMMS. Zirconium compounds were examined for mass spectral characteristics and ion yield patterns F Elemental concentrations of coal petrographic fractions were examined by LMMS examination of various maceral groups F The wide range of LMMS applications is indicative of its growing popularity for elemental microanal sis.
Although quantitation problems inherent in LMMS t d k i q u e s persist, its sensitive microanalytical capabilities prove unique in many biological and environmental applications. Increasing use of this technique in combination with other microanalytical methods e. The RIMS technique differs from other laser ionization mass s ectrometric methods in several respects, the most notable Being the use of resonant laser frequencies to more ef iciently and selectively photoionize specific elements an even isotopes.
The ionization specificity afforded by RIMS theoretically precludes isobaric atomic and molecular interferences, opening new possibilities in atomic mass spectrometry that have traditionally been plagued by these MS nemeses. Use of RIMS depends on the generation of free atoms prior to photoionization, and many traditional atom sources have been utilized with the RIMS technique; the abilities to utilize a variety of atom generators and to optimize atomization independently from ion generation constitute secondary advantages of the technique.
The RIMS technique has been the subject of several recent in-depth reviews. The RIMS research group at Oak Ridge National Laboratory has summarized the principles, instrumentation, and features of the method in several excellent reviews G 1 4 3.