Ionization mass spectrometer

Neder H, Heusser G, Laubenstein M (2000) Low-level y-ray germanium-spectrometer to measure veiy low primordial radionuclide concentrations. ApplRadiat Isot 53 191-195 Palacz ZA, Freedman PA, Walder AJ (1992) Thorium isotope ratio measurements at high abundance sensitivity using a VG 54-30, an energy-filtered thermal ionization mass spectrometer. Chem Geol 101 157-165... 

Atmospheric pressure ionization mass spectrometers, 13 468 Atmospheric pressure chemical ionization (APCI) liquid chromatography, 4 625 Atmospheric Pressure MALDI, 15 658 Atmospheric stability, of organic semiconductors, 22 210... 

M.A. Baldwin and F.W. McLafferty, Liquid chromatography-mass spectrometry interface. I The direct introduction of liquid solutions into a chemical ionization mass spectrometer, Org. Mass Spectrom., 7 (1973) 1111-1112. 

Personnel working in some programs at the Los Alamos National Laboratory (LANL) may handle radioactive materials that, under certain circumstances, could be taken into the body. Employees are monitored for such intakes through a series of routine and special bioassay measurements. One such measurement involves a thermal ionization mass spectrometer. In this technique, the metals in a sample are electroplated onto a rhenium filament. This filament is inserted into the ion source of the mass spectrometer and a current is passed through it. The ions of the plutonium isotopes are thus formed and then accelerated through the magnetic held. The number of ions of each isotope are counted and the amount of Pu-239 in the original sample calculated by comparison to a standard. 

The two membranes most used for protein work are nitrocellulose and polyvi-nylidene fluoride (PVDF). Both bind proteins at about 100 pg/cm2. Nitrocellulose is the best membrane to use in the initial stages of an experiment. PVDF is used when proteins are to be sequenced or placed into a (matrix-assisted laser desorption ionization) mass spectrometer. PVDF can withstand the harsh chemicals of protein sequenators and the heat generated by mass spectrometer lasers, whereas nitrocellulose cannot. 

The relatively small mass differences for most of the elements discussed in this volume requires very high-precision analytical methods, and these are reviewed in Chapter 4 by Albarede and Beard (2004), where it is shown that precisions of 0.05 to 0.2 per mil (%o) are attainable for many isotopic systems. Isotopic analysis may be done using a variety of mass spectrometers, including so-called gas source and solid source mass spectrometers (also referred to as isotope ratio and thermal ionization mass spectrometers, respectively), and, importantly, MC-ICP-MS. Future advancements in instrumentation will include improvement in in situ isotopic analyses using ion microprobes (secondary ion mass spectrometry). Even a small increase in precision is likely to be critical for isotopic analysis of the intermediate- to high-mass elements where, for example, an increase in precision from 0.2 to 0.05%o could result in an increase in signal to noise ratio from 10 to 40. 

Iron. Fe has 4 isotopes of which the heaviest Fe has a very small abimdance of about 0.3%. The precision of thermal ionization mass spectrometers is around 10 s on this isotope and there is only a hint in some normal inclusions for an excess in 5 Fe (VoUcening and Papanastassiou 1989). Recent ICPMS measurements at the 2 s precision level display normal isotopic compositions for Fe in planetary materials but no Allende inclusion was reported in this study (Kehm et al. 2003). If excesses of similar magnitude to Ca, Ti, Cr were present they would not be clearly resolved in agreement with the observations. When Fe and Fe are used to correct for instrumental mass fractionation, Fe exhibits normal abundances, suggesting all three isotopes are present in solar relative abundances. 

The observed range of natural variations of 5 Ca is about 4 to 5%o in terrestrial materials and up to 50%o in high temperature condensate minerals in carbonaceous chondrites. The typical reproducibility of measurements is about +0.15%o. Broader application of Ca isotope measurements in geochemistry may be possible, particularly if the reproducibility can be improved to 0.05%o to 0.03%o. There is hope that this can be achieved either with inductively coupled plasma source mass spectrometry (Halicz et al. 1999) or with a new generation of multi-collector thermal ionization mass spectrometers (Heuser et al. 2002). 

Rollgen, F.W. Heinen, H.J. Formation of Multiply Charged Ions in a Field Ionization Mass Spectrometer. Int. J. Mass Spectrom. Ion Phys. 1975, 77, 92-95. 

C. The Time-Resolved Atmospheric Pressure Ionization Mass Spectrometer (TRAPI)... 

S. Bajic, Electrospray and atmospheric pressnre chemical ionization mass spectrometer and ion source. Patent 5756994, May 26, 1998. 

Figure 5 Examples of Data Generated on an Electrospray Ionization Mass Spectrometer, (a) Proteins Typically Produce Positive, Multiply Charged Ions and (b) Oligonucleotides Generate Negative, Multiply Charged Ions. Inset are the Computer-Generated Molecular Weight Spectra...

FIGURE 11.32 Schematic diagrams of two chemical ionization mass spectrometers used to measure HNO, (adapted from Mauldin et at., 1998 and Huey el at., 1998). 

FIGURE 11.69 Schematic diagram of single-particle laser ionization mass spectrometer (adapted from Gard et at., 1997). 

Thermal-ionization mass spectrometers use a hot filament to ionize the sample. The element of interest is first purified using wet chemistry and then is loaded onto a source filament, often along with another substance that makes ionization easier and a more stable function of temperature. The filament is heated and as the sample evaporates, it is ionized. Both positive and negative ions can be created by thermal ionization, depending on the electronegativity of the element to be measured. Thermal-ionization mass spectrometers are used to measure a wide variety of elements, including magnesium, calcium, titanium, iron, nickel, rubidium, strontium, neodymium, samarium, rhenium, osmium, uranium, lead, and many others. 

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