Coupling spectrometry

Although GGMS is the most widely used ana lytical method that combines a chromatographic sep aration with the identification power of mass spectrometry it is not the only one Chemists have coupled mass spectrometers to most of the mstru ments that are used to separate mixtures Perhaps the ultimate is mass spectrometry/mass spectrome try (MS/MS) m which one mass spectrometer gener ates and separates the molecular ions of the components of a mixture and a second mass spec trometer examines their fragmentation patterns ... 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

If a sample solution is introduced into the center of the plasma, the constituent molecules are bombarded by the energetic atoms, ions, electrons, and even photons from the plasma itself. Under these vigorous conditions, sample molecules are both ionized and fragmented repeatedly until only their constituent elemental atoms or ions survive. The ions are drawn off into a mass analyzer for measurement of abundances and mJz values. Plasma torches provide a powerful method for introducing and ionizing a wide range of sample types into a mass spectrometer (inductively coupled plasma mass spectrometry, ICP/MS). 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

Samples to be examined by inductively coupled plasma and mass spectrometry (ICP/MS) are commonly in the form of a solution that is transported into the plasma flame. The thermal mass of the flame is small, and ingress of excessive quantities of extraneous matter, such as solvent, would cool the flame and might even extinguish it. Even cooling the flame reduces its ionization efficiency, with concomitant effects on the accuracy and detection limits of the ICP/MS method. Consequently, it is necessary to remove as much solvent as possible which can be done by evaporation off-line or done on-line by spraying the solution as an aerosol into the plasma flame. 

Plasma torches and thermal ionization sources break down the substances into atoms and ionized atoms. Both are used for measurement of accurate isotope ratios. In the breakdown process, all structural information is lost, other than an identification of elements present (e.g., as in inductively coupled mass spectrometry, ICP/MS). 

This is the basic process in an inductively coupled plasma discharge (ICP). The excited ions can be examined by observing the emitted light or by mass spectrometry. Since the molecules have been broken down into their constituent atoms (as ions) including isotopes, these can be identified and quantified by mass spectrometry, as happens with isotope ratio measurements. 

Samples to be examined by inductively coupled plasma and mass spectrometry (ICP/MS) are frequently in the form of a solution of an analyte in a solvent that may be aqueous or organic. 

Laser-desorption mass spectrometry (LDMS) or matrix-assisted laser desorption ionization (MALDI) coupled to a time-of-flight analyzer produces protonated or deprotonated molecular ion clusters for peptides and proteins up to masses of several thousand. 

ICP/MS. inductively coupled plasma and mass spectrometry used as a combined technique ICR. ion cyclotron resonance (spectroscopy)... 

Montaudo, G. and Lattimer, R.P., Mass Spectrometry of Polymers, CRC Press, Boca Raton, FL, 2001. Montaser, A., Inductively Coupled Plasma Mass Spectrometry, Wiley, Chichester, U.K., 1998. 

Wangzhao, Z., Advanced Inductively Coupled Plasma Mass Spectrometry Analysis of Rare Elements, Balkema Publishers, 1999. 

To measure trace metals to the levels required in the guidelines involves the use of state-of-the-art instmmentation such as inductively coupled plasma/mass spectrometry (icp/ms). 

Gold is a useflil caUbration standard for this method (see Radioactive tracers). Whereas similar sensitivities can be achieved by inductively coupled plasma mass spectrometry (qv), the latter requires more extensive sample preparation to overcome interference by other metals such as copper (64). 

The use of separation techniques, such as gel permeation and high pressure Hquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of siUcones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of siUcone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is appHcable up to 10,000 Da (487). 

Highly sensitive iastmmental techniques, such as x-ray fluorescence, atomic absorption spectrometry, and iaductively coupled plasma optical emission spectrometry, have wide appHcation for the analysis of silver ia a multitude of materials. In order to minimize the effects of various matrices ia which silver may exist, samples are treated with perchloric or nitric acid. Direct-aspiration atomic absorption (25) and iaductively coupled plasma (26) have silver detection limits of 10 and 7 l-lg/L, respectively. The use of a graphic furnace ia an atomic absorption spectrograph lowers the silver detection limit to 0.2 l-ig/L. 

M. Thompson and J. N. Walsh, eds.. Handbook of Inductively Coupled Plasma Spectrometry, 2nd ed.. Chapman Hall, New York, 1989. 

A. Montaser and D. W. GoHghdy, eds.. Inductively Coupled Plasmas in Analytical Atomic Spectrometry, 2nd ed., VCH PubHshers, New York, 1992. 

Numerous methods have been pubUshed for the determination of trace amounts of tellurium (33—42). Instmmental analytical methods (qv) used to determine trace amounts of tellurium include atomic absorption spectrometry, flame, graphite furnace, and hydride generation inductively coupled argon plasma optical emission spectrometry inductively coupled plasma mass spectrometry neutron activation analysis and spectrophotometry (see Mass spectrometry Spectroscopy, optical). Other instmmental methods include polarography, potentiometry, emission spectroscopy, x-ray diffraction, and x-ray fluorescence. 

Atomic Absorption/Emission Spectrometry. Atomic absorption or emission spectrometric methods are commonly used for inorganic elements in a variety of matrices. The general principles and appHcations have been reviewed (43). Flame-emission spectrometry allows detection at low levels (10 g). It has been claimed that flame methods give better reproducibiHty than electrical excitation methods, owing to better control of several variables involved in flame excitation. Detection limits for selected elements by flame-emission spectrometry given in Table 4. Inductively coupled plasma emission spectrometry may also be employed. 

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

Inductively coupled argon plasma (icp) and direct current argon plasma (dcp) atomic emission spectrometry are solution techniques that have been appHed to copper-beryUium, nickel—beryUium, and aluminum—beryUium aUoys, beryUium compounds, and process solutions. The internal reference method, essential in spark source emission spectrometry, is also useful in minimizing drift in plasma emission spectrometry (17). Electrothermal (graphite... 

The mass spectrometer (ms) is a common adjunct to a chromatographic system (see Mass spectrometry). The combination of a gas chromatograph for component separation and a mass spectrometer (gc/ms) for detection and identification of the separated components is a powerful tool, particularly when the data are collected usiag an on-line data-handling system. QuaUtative information inherent ia the separation can be coupled with the identification of stmcture and relatively straightforward quantification of a mixture s components. 

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