Mass spectrometric systems

As in all mass spectrometric systems, the postulated ion structures cannot be directly verified, but recent advances in ion kinetic energy spectroscopy (see Section VI) allow one to prove that two ions of the same mass from different sources have either identical or differing structures. Ionic structures tend to be drawn based on common sense and chemical intuition. 

This method allows a quantitative analysis of BAs present in biological fluids (free, and glycine- and taurine-conjugated forms) in a single chromatographic run, performed with an HPLC mass spectrometric system equipped with an electrospray interface [33]. 

By using non-normal beam incidence and curved pole pieces, the effective radius of curvature of the magnetic sector field is extended, which results in an increase in dispersion and an improvement in the abundance sensitivity of the mass spectrometric system.4... 

Different mass spectrometric systems are designed to make use of all the ion sources, ion separation and ion detection systems - as described in the previous chapters. 

Hieftje and co-workers first reported a design for ICP-ToF mass spectrometric systems with both orthogonal acceleration (oa) and axial acceleration (aa) geometry.39 11 The different experimental setups of ICP-ToF mass spectrometers with orthogonal and axial acceleration are compared in Figures 5.10 and 5.11. Both instruments possess a time-of-flight analyzer with a reflectron to improve the mass resolution. 

Lopshire [188] explored the exchange reaction of chlorine by oxygen with polychlorobiphenyl anions as a method of compound-selective polychloro-biphenyl congener detection in a gas chromatography-mass spectrometric system. Multiple reaction monitoring allowed separate chromatograms to be detected for each different polychlorobiphenyl composition from tetra-through nonachloro. 

There have been great advances in mass spectrom-etric instrumentation over the past decade. All of the instruments described above are rugged and available for routine use. While these are not the only tandem mass spectrometric systems available, when used together, they provide a powerful complement for metabolite characterization experiments. A flow chart illustrating the complementary nature and effective utilization of these various MS/MS techniques is shown in Fig. 1. The most effective use of these instruments involves setting up the front end of the systems identically. All systems should be fitted with the same LC and injection system and the mass spectrometers should be set up in parallel with a radio flow detector. In this manner, samples can be easily moved from one... 

Selection of the analytical instrumentation for the analysis of the pyrolysate is a very important step for obtaining the appropriate results on a certain practical problem. However, not only technical factors are involved in this selection the availability of a certain instrumentation is most commonly the limiting factor. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS) are, however, the most common techniques utilized for the on-line or off-line analysis of pyrolysates. The clear advantages of these techniques such as sensitivity and capability to identify unknown compounds explain their use. However, the limitations of GC to process non-volatile samples and the fact that larger molecules in a pyrolysate commonly retain more structural information on a polymer would make HPLC or other techniques more appropriate for pyrolysate analysis. However, not many results on HPLC analysis of pyrolysates are reported (see section 5.6). This is probably explained by the limitations in the capability of compound identification of HPLC, even when it is coupled with a mass spectrometric system. Other techniques such as FTIR or NMR can also be utilized for the analysis of pyrolysates, but their lower sensitivity relative to mass spectrometry explains their limited usage. 

A special type of mass spectrometric system is an MS/MS (e.g. [45]). In an MS/MS system the ions are generated by any of the available procedures (common El or Cl ionizations are used). The process continues with the ion separation using one of the systems previously described. A particular ion A (named parent ion) is then selected and further dissociated by collision with the molecules of a gas N (collision induced dissociation-CID or collision activated dissociation-CAD) in a reaction zone of the MS/MS system. The common reaction taking place in the CID zone can be described as follows ... 

Degradative methods based on pyrolysis are the subject of renewed interest due to the identification power offered by gas chromatography-mass spectrometric systems (GC-MS) (Wershaw and Bohner, 1969 Martin et al., 1977 Meuzelaar et al., 1977 Bracewell and Robertson, 1976). There are two main pyrolysis techniques (1) controlling the decomposition kinetics by temperature programming and (2) the use of quasi-instantaneous heating (e.g.. Curie point pyrolysis). The later technique avoids most recombination reactions, but does not allow kinetic control. The pyrolysis effluent can be detected directly (Rock-Eval method) or after chromatographic fractionation. 

In many cases, the identity of the analyte will be known nonetheless, it is highly desirable that this be confirmed to avoid the possibility that an interfering compound fortuitously has, for example, the same GC or HPLC retention time as that of the desired analyte. Indeed, many protocols that are now advocated use mass spectrometric systems so that this control is automatically incorporated. Samples may be spiked with internal standards to simplify calculation and eliminate small errors in pipetting and injection, or surrogate standards may be employed where, for example, incomplete extraction of the analyte is unavoidable. When MS is used as the detection system, analytes labeled with suitable isotopes have been widely used for PAHs, fully deuterated standards, and for PCBs and agrochemicals, Relabeled compounds. For partially labeled standards of analytes, care must be exercised in their choice if it is intended to analyze for metabolites of a substrate in which the label may have been lost. 

A convenient way to investigate the elemental and isotopic composition of the upper surface layers of small bodies of the Solar system is to use small-size laser mass spectrometers, mounted on a lander. Optimal for the purpose is a reflectron type time-of-flight mass analyzer with laser evaporation and ionization of the target, called LASMA (LASer Mass Analyser). It was created on the basis of a laboratory prototype, initially developed for the LIMA-D laser mass spectrometric system on the PHOBOS experiment, a space mission to the Mars satellite. A spin-off modification of the LASMA device was further developed for the special purposes of environmental research. 

Tarkiainen, V., Kotiaho, T., Mattila, I. et al. (2005) On-line monitoring of continuous beer fermentation process using automatic membrane inlet mass spectrometric system. Talanta, 65... 

Mass spectrometric systems come in a variety of configurations multiple sample introduction and ionization methods may be combined with single analyzers or coupled into MS/MS formats, using the same or different types of mass analyzer. Although most instrument formats are capable of multiple functions, one configuration is often better suited to a specific analysis. For instance, the collection of spectra in TOF instruments is much faster and more sensitive than with quadrupoles therefore, TOF systems... 

We have shown some examples of the type of results currently obtained by this combined thermogravimetric atmospheric pressure chemical ionization mass spectrometric system. This study leads the way to further developmental work in the identification and quantitation of polymer pyrolysis reactions. 

A low-resolution mass measurement is a simple procedure and can be performed with most of the mass spectrometric systems discussed in Chapter 3. The instrument is set up at a resolving power (RP) above 1000. At this low resolving power, the molecular ions of most organic compounds that differ by a unit mass are well separated. The mass spectrometer is first mass-calibrated with an external calibration procedure. During the calibration scan, the computer stores the peak centroid (the center of gravity) time and the area of each peak. The mass of the ion is related exponentially to the peak centroid time ... 

Mass spectrometric studies of a-BN have been performed in laser-induced plasmas produced with pulsed Nd-YAG-Lasers. The mass spectrometric systems were either of Mattauch-Herzog geometry [38 to 40] or based on a modular quadrupole system [41 to 43]. It was shown that a typical alternating abundance distribution is observed for the [B N. i]" and [BnNp.g]" cluster ions in which cluster ions with odd numbers of atoms prevail. Clusters up to BgNg have been recorded (see Fig. 4-19, p. 42). The listing in Table 4/6, p. 42, includes identified ions of low intensity [38]. a-BN/graphite mixtures have also been investigated [38 to 40]. 

Chapter 6 describes the concept of hybrid mass spectrometric system with ion attachment technique as ionization method. A combined (hypemated) MS represents time-of-flight (TOP), ion trap quadmpole, ion mobility spectroscopy, ion cyclotron resonance (ICR) or aerosol MS, while descriptions of specially designed inlet system include chromatographic introduction (inlets), and various pyrolysis probes for evolved gas analysis. Some applications of each technology are presented, together with representative and/or illustrative examples. In addition, development of portable lAMS is provided along with explanations and spectral applications. 

This liquid chromatography - mass spectrometric system enables additives to be determined in polypropylene in amounts down to 0.01%. 

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