Mass-spectrometric detector instruments

Over the past decade Inductively Coupled Plasma (ICP) sources, in particular coupled with Mass Spectrometry (MS) instruments, have shown an immense potential for multielement analysis in environmental samples (88). These capabilities have been obtained thanks to the combination of the great ionization energy of a plasma source with the high sensitivity and selectivity of the mass spectrometric detector. Since polar snow and ice are considered as the purest material on the earth surface, these environmental matrices constitute the ideal samples for ICP-MS since potential interferences formed in the plasma are kept at a minimum level. 

Mass spectrometric detectors for capillary electrophoresis are necessarily post-column detectors and must be interfaced to the cathodic end of the capillary. These detectors consist of four main components the interface, that joins the capillary to the ion source, the ion source, that generates ionic fragments from neutral analyte species, the mass analyzer, that distinguishes ions by their mass/charge (m/z) values, and the ion detector, that measures and amplifies the signal. The principles and instrumentation of bioanalytical MS are explained in Chapter 15. 

The mass spectrometric detector is often coupled to GC to provide a very sensitive separation and detection instrument in one. This system is discussed in more detail in the section on hyphenated (hybrid) techniques. 

CE can be used as a qualitative or quantitative technique. An example of a CE instrument is shown in Figure 3.31. Qualitative information allows a substance to be identified on the basis of migration time comparisons between a standard and the sample. Alternatively, and more definitively, the use of a mass spectrometric detector enables the molecular weight of eluting components to be determined and, as long as those molecular weights... 

Tbe reader new to mass spectrometry is advised to consult an appropriate introductory text [2-9]. A few mass spectrometric terms will be explained here by way of background and to outline the principles of choosing a flame ionization detector, ions are produced in the mass spectrometric detector, but the mass spectrometer is able to analyze these ions further according to their molecular weights or rather, mass-to-charge ratios (m/z, see below) to provide a mass spectrum. Different principles are employed to achieve this in a variety of types of mass spectrometer. The instruments most commonly used in GC—MS are known as magnetic sector, quadrupole and ion trap mass spectrometers. Their differences are not further described here. Bench-top systems are of the quadrupole or ion trap type. 

The book comprises 19 chapters that are divided into Sections I and II. Section I contains Chapters 1 through 9, which provide an overview of chromatographic thin layers, special instrumentation for the TLC-MS coupling, and various different mass spectrometric techniques that can be directly or indirectly combined into the planar chromatography-MS methodologies. Gel electrophoretic layers are additionally included in this book because they formally fall within the scope of the definition of a thin layer and can be coupled offline with mass spectrometric detectors. Section II... 

From the basic setup, just described, one may conclude that an FA instrument is a modular instrument, consisting of an ion source, a flow reactor tube, and a (mass spectrometric) detector as the building blocks. Each of the building blocks may be modified or adapted to the specific needs of the experiment to be performed. 

Gas chromatography, coupled with flame-ionisation, electron capture (for halogenated species) and mass spectrometric detectors, is the most popular tool for determination of SVOCs in melted snow samples [44]. A prerequisite is the efficient separation of the analytes from the aqueous matrix, which can be accomplished using filtration onto quartz fibre filters and sohd phase extraction [88]. Solid phase micro-extraction, which utilises equihbrium-based adsorption of analytes onto a polymer fibre bundle, has also been proposed and tested in laboratory studies [13, 89]. Both methods allow for an efficient transfer into the injection port of a gas chromatograph without water contamination. Directly coupled inlet sampler with GC-EID instrumentation has also been used [90]. The air sample was pre-concentrated using adsorbents (Carbotrap B, Carbosieve), followed by heating and collection on a cryofocuser (a fused silica capillary tube packed with... 

Qualitative and quantitative analyses with HPLC are very similar to those with GC (Sections 12.7 and 12.8). In the absence of diode array, mass spectrometric, and FTIR detectors that give additional identification information, qualitative analysis depends solely on retention time data, tR and C (Remember that tR is the time from when the solvent front is evident to the peak) Under a given set of HPLC conditions, namely, the mobile and stationary phase compositions, mobile phase flow rate, column length, temperature (when the optional column oven is used), and instrument dead volume, the retention time is a particular value for each component. It changes only when one of the above parameters changes. Refer to Section 12.7 for further discussion of qualitative analysis. 

In the last twenty years, many of the developed and validated high performance liquid chromatography methods with conventional diode array or fluorescence detectors (DAD, FLD) were improved and substituted by new hyphenation with mass spectrometric instrumentation and/or NMR, especially for the analyses of raw materials derived from Natural sources. The main goal of this coupling is achieved by improvement of selectivity and sensitivity of new instrumental configurations [7], Furthermore, with these configurations it is possible to obtain, in only one analysis, the complete chemical structure elucidation, identification and quantification of targeted compounds. 

Compared to previously reported instrument configuration, is possible also to couple two different detector systems after 2D-HPLC in order to improve the identification and structural elucidation of targeted compound, for example mass spectrometric and NMR detectors. 

Samples are introduced into the capillary by either electrokinetic or hydrodynamic or hydrostatic means. Electrokinetic injection is preferentially employed with packed or monolithic capillaries whereas hydrostatic injection systems are limited to open capillary columns and are primarily used in homemade instruments. Optical detection directly through the capillary at the opposite end of sample injection is the most employed detection mode, using either a photodiode array or fluorescence or a laser-induced fluorescence (LIF) detector. Less common detection modes include conductivity [1], amperometric [2], chemiluminescence [3], and mass spectrometric [4] detection. 

Equations (8)—(10) apply to all the various types of mass spectrometric experiments and these expressions define the nature of the information the experiments seek to provide. In Sect. 3, the various experimental techniques are reviewed and each in turn is related to these basic expressions [eqn. (8) etc.]. In reviewing results in subsequent sections (Sects. 4—8), it is assumed, unless there is evidence to the contrary, that experiments have been conducted with adequate attention to all the many instrumental effects. That is to say, it is assumed that reported ion intensities, abundances, peak heights, voltages or ion currents do accurately portray the numbers (per time), 7, of ions (or ion currents) arriving at the detector and that these numbers, 7m in the case of fragment ions m, are a true measure of the numbers, Nm, of ions formed within the observation window of the experiment. 

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