Mass spectrometric techniques, developments

M. Montes Bayon, T. D. Grant, J. Meija, J. A. Caruso, Selenium in plants by mass spectrometric techniques Developments in bio-analytical methods, J. Anal. Atom. Spectrom., 17 (2002), 1015 D1023. 

Centini, R, Offidani, C., Camevale, A., Chiarotti, M., Barni Comparini, I., Determination of Morphine in Hair by Immunochemical and Gas Chromatographic Mass Spectrometric Techniques, Development in Analytical Methods in Pharmaceutical, Biomedical, and Forensic Sciences, 1st ed., Piemonte, G., Tagliaro, R, Marigo, M., Frigerio, A., Eds., Plenum Press, New York, 1987,107. Moeller, M. R., Mueller, C., The Detection of 6-Monoacetylmorphine in Urine, Serum and Hair by GC/MS and RIA, Forensic Sci. Int., 70,125,1995. 

Mass spectra of short-lived, unstable episelenides were obtained by taking advantage of a mass spectrometric technique developed for the time-resolved detection of transient intermediates in flash-photolyzed systems <66JA4277>. Detection does not depend on the electronic absorption characteristics of the transient, and, in combination with kinetic absorption spectroscopy, the technique assumes great flexibility. The apparatus consists, essentially, of a photolysis cell attached to a small leak into the ion source of an Atlas CH4 mass spectrometer. Selected mass peaks can be studied with a response time of a few milliseconds, and thereafter at times limited by bleeding of the photolyzed mixture into the ion chamber. Typical photolytic flash energies were 480 calories, passed into a reaction volume of 5 ml. 

Utilizing the continuous mass spectrometric techniques developed by Arnot and co-workers and Hornbeck and Molnar in which reaction identification is made from considerations of the appearance potentials of the product ions and from the effects of electron energy, pressure, and repeller potential on product-ion intensity, homonuclear associative ionization reactions have been reported in helium, " in neon, "- " " i46A9,5o,52-si,62) krypton,< " " - " > in... 

In this chapter we discuss improvements documented in the literature over the past decade in these areas and others. Chemical procedures, decay-counting spectroscopy, and mass spectrometric techniques published prior to 1992 were previously discussed by Lally (1992), Ivanovich and Murray (1992), and Chen et al. (1992). Because ICPMS methods were not discussed in preceding reviews and have become more commonly used in the past decade, we also include some theoretical discussion of ICPMS techniques and their variants. We also primarily focus our discussion of analytical developments on the longer-lived isotopes of uranium, thorium, protactinium, and radium in the uranium and thorium decay series, as these have been more widely applied in geochemistry and geochronology. 

Mass spectrometric techniques for analysis of Th- U disequilibria were first developed to date corals for paleoclimate research (Edwards et al. 1987). Soon thereafter, workers at Los Alamos National Laboratory (LANE) developed methods for silicate analysis by TIMS (Goldstein et al. 1989). Typical TIMS analysis of MORE requires 0.5 to 1 gram of material in order have an analyzable load of 100 ng of Th. TIMS analyses of U and Th last 2-3 hrs and produce a precision of 0.5-2% (2a). SIMS techniques for measuring Th isotopes have also been developed (England et al. 1992 Layne and Sims 2000). Analysis of Ra and Pa isotopes by TIMS was developed in the early 1990 s significantly increasing the sensitivity over decay counting analysis (Volpe et al. 1993 Cohen and Onions 1993 Pickett et al. 1994 Chabaux et al. 1994). 

Of note are the values for °Th and as the revised values postdate the development of mass spectrometric techniques for measurement of U and Th in natural materials. Data published prior to Cheng et al. (2000b) does use not use the revised values whereas data published subsequently may or may not use the new values. The revised half-lives do have a small, but significant effect on calculated °Th ages, particularly ages older than about 100 ka. Furthermore, the new value for the half-life changes values as these are calculated from measured atomic ratios using... 

The development of mass spectrometric techniques for nuclide identification using a tandem Van de Graaff accelerator at the University of Rochester Nuclear Structure Laboratory by H. Gove, K. Purser, A. Litherland, and numerous associates has provided an excellent means for the precise measurement of 36C1 concentrations in natural water [43]. Thus far, about 40 groundwater related samples which have been collected and purified chemically by H. Bentley have been analyzed for 36C1 by D. Elmore, H. Bentley, and others using the University of Rochester machine. Some of these samples are listed in Table 2. 

Shortly after the development of the early mass spectrometers, Li isotopes were identified by Francis Aston (1932). Although mass spectrometric techniques are those most commonly applied to the measurement of isotope ratios in geochemistry, attempts to quantify Li isotopes have been made using non-mass based emission methods (e.g., atomic absorption Zaidel and Korennoi 1961 various nuclear methods Kaplan and Wilzbach 1954 Brown et al. 1978 ... 

The development of mass spectrometric techniques, such as fast atom bombardment mass spectrometry (FAB-MS), ° ° Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), ° and tandem mass spectrometry (MS"), ° allowed enantiodiscrimination of chiral ion-dipole complexes the gas phase. These techniques and others will be illustrated in detail in the next Section 3. 

As noted above, mass spectrometric techniques such as MALDI-TOF have now been developed to the stage where they are extremely useful for analysis of the molecular weights of polymers. This technique can give molecular ions for macromolecules with molecular weights substantially greater than 10000 and values up to 100 000 have been successfully determined. ... 

The development of a number of mass spectrometric techniques in the late 1960s paved the way for the study of bimolecular chemical reactions of ions with neutral molecules in the gas phase (see, for example, Harrison et al., 1966 McDaniel et al., 1970 Franklin, 1972). While the systems initially investigated were concerned primarily with positive ions and with relatively simple reactions, the underlying potential of such techniques was soon to be explored in a dramatic way. 

Trends in mass spectrometry focus on the improvement of instrumentation, of several techniques in order to minimize sample volume, to improve sensitivity and to reduce detection limits. This is combined with increasing the speed of several analyses, with automation of analytical procedures and subsequently reducing the price of analysis. A minimizing of sample volumes means a reduction of waste volume with the aim of developing green chemistry . Furthermore, new analytical techniques involve a development of quantification procedures to improve the accuracy and precision of analytical data. Special attention in future will be given to the development of hyphenated mass spectrometric techniques for speciation analysis and of surface analytical techniques with improved lateral resolution in the nm scale range. 

Two recently developed mass spectrometric techniques have had a major impact on the analysis of large biomolecules matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS). MALDI-MS was first introduced by Karas and Hillenkamp66 and Tanaka et al.61 in 1988 and has experienced an exponential development. It has become a widespread soft ionization technique for bioorganic samples, especially large biomolecules. Fenn and co-workers68 first published the successful soft ionization technique for... 

Instrumental layouts and developments in AMS are reviewed by Kutschera.195 Today AMS is the most powerful, sensitive and selective mass spectrometric technique for measuring long-lived radionuclides at the level of natural isotopic abundances (10-16 to 10-12). Accelerator mass spectrometry (AMS) allows uranium isotope ratio measurements with an abundance sensitivity for 236U in the range of l(rlo-10 l2.l98J"... 

Certified reference materials (CRMs) are mainly applied to validate the analytical procedure developed for routine analysis in order to determine the accuracy of analytical data, the recovery for selected elements, the uncertainty of trace element determination and the detection limits. Otherwise, in solid-state mass spectrometric techniques, such as SSMS, LA-ICP-MS, GDMS, SNMS or SIMS, one point calibration using CRMs has been established as an important calibration strategy to obtain reliable analytical data. The one point calibration is performed using the experimentally determined relative sensitivity coefficients (RSCs) on a suitable CRM with a similar trace/matrix composition. An RSC of a chemical element is defined as the ratio of the measured element concentration (experimentally determined) divided by the certified element concentration (accepted or recommended value of element concentration) in a given matrix. 

Calibration and quantification procedures are easier in LA-ICP-MS compared to other solid-state mass spectrometric techniques because the laser ablation and the ICP ion source operate at normal pressure and the laser ablation of solid samples and ionization of analytes are separated in space and time. Therefore the advantage of solution calibration in ICP-MS can be applied in this solid-state analytical technique. The introduction of solution based calibration, which is only possible in LA-ICP-MS, was an innovative step in the development of this sensitive mass spectrometric technique. A number of different calibration approaches using aqueous standard solutions in the dual gas flow technique have been discussed by various authors.74 75 In the dual gas flow injection technique , the nebulized standard solution and the laser ablated sample material are mixed in the -piece and the two gas flows from the nebulizer (e.g. ultrasonic nebulizer) and laser ablation chamber are added. Using solution based calibration with the addition of a standard solution, Leach et alP determined minor elements in steel reference materials with a relative accuracy of a few %. In comparison to the so-called dual gas flow technique proposed in the literature, where the argon flow rates through the nebulizer and ablation cell add up to 11 min-1 (e.g. 0.451 min-1 and... 

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