LC-MS interfaces particle beam

Figure 4.5 Schematic of a particle-beam LC-MS interface. From applications literature published by Micromass UK Ltd, Manchester, UK, and reproduced with permission.

The particle beam LC/MS interface must reduce the system pressure to about 1 x 10 6 to 1 x 10 4 torr at which electron ionization occurs. 

Cappiello, A. Famiglini, G. CapiUary-Scale Particle-Beam LC-MS Interface Can Electron Ionization Sustain the Competition J. Am. Chem. Soc. Mass Spectrom. 1998,9, 993-1001. 

Recent advances in electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), thermospray, and particle beam LC-MS have advanced the analyst toward the universal HPLC detector, but price and complexity are still the primary stumbling blocks. Thus, HPLC-MS remains expensive and the technology has only recently been described. Early commercial LC-MS uses particle beam and thermospray sources, but ESI and APCI interfaces now dominate. Liquid chromatography MS can represent a fast and reliable method for structural analyses of nonvolatile compounds such as phenolic compounds (36,37), especially for low-molecular-weight plant phenolics (38), but the limited resolving power of LC hinders the widespread use of its application for phenolics as compared to GC-MS. 

Like continuous-flow FAB, the popularity of particle beam interfaces is diminishing, but systems are still available from commercial sources. During particle beam LC-MS, the HPLC eluate is sprayed into a heated chamber... 

Particle beam LC-MS is a rapidly developing complimentary interface to thermospray techniques and provides a method of linking conventional HPLC systems with eluant flow-rates of 0.3-1.0mlmin , to an El ion source to obtain the classical El spectra which can be compared to conventional reference spectra (Figure 7.12). A capillary GC column may be connected to the same interface [10]. LC eluant enters the interface together with a stream of helium to form an aerosol of droplets which move through the desolvation chamber maintained at room temperature and pressure. The... 

Yu and co-workers [26] discussed LC interfaces for bench-top single quadruple LC-MS. The two most popular interfaces are particle beam and atmospheric pressure ionisation types. The system was applied to the analysis of additives in PP. Dilts [27] used a photodiode array detector coupled with particle beam LC-MS to characterise degradation of Irganox 1010, Irganox 1076 and Irgafos 16S in polyolefins. 

Flow limitations restrict application of the DFI interface for pSFC-MS coupling. pSFC-DFI-MS with electron-capture negative ionisation (ECNI) has been reported [421], The flow-rate of eluent associated with pSFC (either analytical scale - 4.6 mm i.d. - or microbore scale 1-2 mm, i.d.) renders this technique more compatible with other LC-MS interfaces, notably TSP and PB. There are few reports on workable pSFC-TSP-MS couplings that have solved real analytical problems. Two interfaces have been used for pSFC-EI-MS the moving-belt (MB) [422] and particle-beam (PB) interfaces [408]. pSFC-MB-MS suffers from mechanical complexity of the interface decomposition of thermally labile analytes problems with quantitative transfer of nonvolatile analytes and poor sensitivity (low ng range). The PB interface is mechanically simpler but requires complex optimisation and poor mass transfer to the ion source results in a limited sensitivity. Table 7.39 lists the main characteristics of pSFC-PB-MS. Jedrzejewski... 

Table 7.53 shows the main characteristics of LC-PB-MS. Of all LC-MS interface methods, LC-PB-MS comes closest to GC-MS (Scheme 7.7). The particle beam is an acceptable choice in cases where sensitivity, volatility and analyte polarity are not an issue. Usually, the function of UV is added to LC-PB-MS this allows the investigation of peak homogeneity. Drawbacks of LC-PB-MS are the low sensitivity and the nonlinearity... 

Only the particle-beam interface produces El spectra for direct comparisons with computerized library spectra of fragmentation patterns. The other systems enable the relative molecular mass (RMM) of analytes up to 105 and above to be established. An example of an HPLC-APCI separation and identification of some benzodiazepine tranquillizers is shown in Figure 4.39. The most appropriate choice of LC-MS interface for a particular... 

Fig. 12.8. LC-MS interfaces (a) moving belt interface, (b) particle beam interface. By courtesy of Thermo Finnigan, Bremen.

The use of liquid chromatography-mass spectrometry (LC-MS) is becoming more popular because of the increasing number of LC-MS interfaces commercially available thermospray (TSP), particle beam (PB), and atmospheric pressure ionization (API). Coupled with mass spectroscopy, HPLC provides the analyst with a powerful tool for residue determination. 

There are other LC/MS interfaces that are less commonly used than ESI and APCI, but are often employed by researchers for analysis of nonpolar or neutral compounds, including particle beam and atmospheric pressure photoionization (APPI). 

Medium-pressure Cl at ion-source pressures between 1 and 2000 Pa is widely used. In LC-MS, it is important in particle-beam and thermospray interfacing. Either an externally-added reagent gas like methane, isobutane, or ammonia is... 

Over 30 years of liquid chromatography-mass spectrometry (LC-MS) research has resulted in a considerable number of different interfaces (Ch. 3.2). A variety of LC-MS interfaces have been proposed and built in the various research laboratories, and some of them have been adapted by instmment manufacturers and became commercially available. With the advent in the early 1990 s of interfaces based on atmospheric-pressure ionization (API), most of these interfaces have become obsolete. However, in order to appreciate LC-MS, one carmot simply ignore these earlier developments. This chapter is devoted to the older LC-MS interfaces, which is certainly important in understanding the histoiy and development of LC-MS. Attention is paid to principles, instrumentation, and application of the capillary inlet, pneumatic vacuum nebulizers, the moving-belt interface, direct liquid introduction, continuous-flow fast-atom bombardment interfaces, thermospray, and the particle-beam interface. More elaborate discussions on these interfaces can be found in previous editions of this book. 

The two chapters that were selected for this topic one on GC-ion trap mass spectrometry, by SabUer and Fujii and the other by Schroder on LC-MS in environmental analysis give an excellent contribution to the application of GC-MS and LC-MS to environmental analysis. Both chapters include many practical aspects and examples in the environmental field and also cover the historical perspective of the techniques and show the perspective on ionisation and scanning modes. Advances achieved in GC-ion trap by the use of external ion sources and GC/MS/MS possi-bihties are discussed. The LC-MS chapter provides an overview of the first applications of LC/MS interfacing systems, such as moving belt, direct Uquid introduction (DLI) and particle beam (PB), and then on the more recent soft ionisation techniques, like thermospray and atmospheric pressure ionisation interfacing systems. 

In the past 10 years, the manner in which LC-MS analysis is performed has significantly changed. While in the past it was necessary to choose the most appropriate LC-MS interface for a particular application from a list of five possibilities, e.g., the moving-belt interface, the direct-liquid introduction interface, the thermospray interface, the particle-beam interface, and the continuous-flow fast-atom bombardment interface, today all LC-MS technologies are based on API. The two most important... 

Other LC-MS ionization techniques are available but their utility for clinical research is low. Until the advent of ESI and APCI the most popular LC-MS interface was thermospray. Other techniques used with varying degrees of success included flow-FAB, transporter belts, and particle beam interfaces. These have been almost wholly superseded by ESI and APCI. 

Currently, the main breakthrough in environmental analysis is observed in the application of LC-MS and LC-MS/MS techniques. One of the obstacles to routine analytical applications of LC-MS had been the unavailability of rugged and reliable LC-MS interfaces. The development of atmospheric pressure ionization (API) overcame such limitations as poor structural information or sensitivity seen with thermospray (TSP) or particle-beam (PB). API is used as a generic term for soft ionization obtained by different interface/ionization types, such as APCI and electrospray (ESI) that operate under atmospheric pressure conditions. Today, LC-MS has become a routine analytical tool, allowing the detection of polar and nonvolatile compounds not amenable to GC analysis. 

MS is undoubtedly the solution of the near future for LC detection. Improvements made to interfacing devices together with a continuous and sensible diminution of instrumentation costs promote MS as a universal/selective tunable detection system. Atmospheric pressrue electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most robust and popular devices for interfacing MS to LC systems. In Table 9, LC-MS data for some pesticides are given. Although ESI and APCI are more often used, other LC-MS interfaces produce reliable results in pesticide applications thermospray (TSI), particle beam (PBI) and matrix-assisted postsource decay laser desorption/ionization (CID-PSD-MALDI). 

For the HPLC-MS systems, many different ionization techniques have been described in the past. Various interface, ionization methods, and operating techniques applicable to LC-MS are discussed in [117J for instance Thermospray, particle beam, electrospray (ES), field desorption (FD), fast atom bombardment (FAB), time of flight (TOF), etc. The electrospray technique produces a soft ionization for thermally labile compounds, while FAB has the advantage that higher molecular mass samples can be introduced into the mass spectrometer. Table 8 offers a rough guide to the applicability of various LC-MS interfaces. For more detailed information on LC-MS, see [118]. 

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