LC particle beam

LC (particle-beam Simple mass spectra, not informative or ... 

Contrary to the predictions in 1989 (27), LC-MS has not experienced a breakthrough as an analytical technique in the vitamin E area. One research group reported two studies on the determination of liposoluble vitamins in foods and infant formulas by LC-particle beam MS (44,50). Caimi and Brenna coupled HPLC with combustion isotope ratio mass spectrometry for the analysis of mixtures of liposoluble vitamins, including a- and y-tocopherol (171). 

LC can be combined with all kinds of mass spectrometers, but for practical reasons only quadrapolar, magnetic/electric-sector, and TOP instruments are in wide use. A variety of interfaces are used, including thermospray, plasmaspray, electrospray, dynamic fast-atom bombardment (FAB), particle beam, and moving belt. 

Fig. 6. Particle beam lc/ms analysis of a complex ha2ardous waste sample (a) TIC showing peak at 23.23 min (b) mass spectmm of 23.23 min peak of...

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.

Solka, B. H., Particle beam LC-MS spectra of anionic surfactants , in Proceedings of the 40th ASMS Conference on Mass Spectrometry and Allied Topics, Washington, DC, May 31-June 5, 1992, pp. 1464-1465. 

Table 5.8 Polypeptides detected during the LC-electrospray-MS analysis of the tryptic digest from / -lactoglobulin (/ILG). Reprinted from 7. Chromatogr., A, 763, Tnrnla, V. E., Bishop, R. T., Ricker, R. D. and de Haseth, J. A., Complete structnre elncidation of a globular protein by particle beam hqnid chromatography-Fourier transform infrared spectrometry and electrospray hqnid chromatography-mass spectrometry - Seqnence and conformation of / -lactoglobulin , 91-103, Copyright (1997), with permission from Elsevier Science...

See footnote cto Table3 LC/PB/MS = hquid chromatography/particle beam mass spectrometry LC/APcl/ESl-MS/MS = liquid chromtography/atmospheric pressure chemical ionization/electrospray ionization tandem mass spectrometry LC/FTIR = Fourier transform infrared LC/TSP-MS/MS = liquid chromatography/thermospray tandem mass spectrometry LC/TSP-MS = liquid chromatography/thermospray mass spectrometry. 

As with GC, the combination of MS and MS/MS detection with LC adds an important confirmatory dimension to the analysis. Thermospray (TSP) and particle beam (PB) were two of the earlier interfaces for coupling LC and MS, but insufficient fragmentation resulted in a lack of structural information when using TSP, and insufficient sensitivity and an inability to ionize nonvolatile sample components hampered applications using PB. Today, atmospheric pressure ionization (API) dominates the LC/MS field for many environmental applications. The three major variants of API... 

Several other interface designs were introduced over this period, including continuous flow fast atom bombardment (CFFAB)" and the particle beam interface (PBI)," but it was not until the introduction of the API source that LC/MS applications really came to the forefront for quantitative analysis. Early work by Muck and Henion proved the utility of an atmospheric pressure interface using a tandem quadrupole mass spectrometer. 

Dorschel, C., The role of particle-beam LC-MS in separation development,... 

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... 

The obvious alternative for the in-line flow-through cell in HPLC-FTIR is mobile-phase elimination ( transport interfacing), first reported in 1977 [495], and now the usual way of carrying out LC-FTIR, in particular for the identification of (minor) constituents of complex mixtures. Various spray-type LC-FTIR interfaces have been developed, namely, thermospray (TSP) [496], particle-beam (PB) [497,498], electrospray (ESP) [499] and pneumatic nebulisers [486], as compared by Som-sen et al. [500]. The main advantage of the TSP-based... 

LC-MS inlet probes support all conventional HPLC column diameters from mobile phase must be eliminated, either before entering or from inside the mass spectrometer, so that the production of ions is not adversely affected. The problem of removing the solvent is usually overcome by direct-liquid-introduction (DLI), mechanical transport devices, or particle beam (PB) interfaces. The main disadvantages of transport devices are that column... 

Two LC-MS systems were developed, based on nearly full removal of the solvent moving-belt [520] and particle-beam [521], Mechanical transport devices... 

LC-PB-MS is especially suited to NPLC systems. RPLC-PB-MS is limited to low-MW (<500 Da) additives. For higher masses, LC-API-MS (combined with tandem MS and the development of a specific mass library) is necessary. Coupling of LC via the particle-beam interface to QMS, QITMS and magnetic-sector instruments has been reported. In spite of the compatibility of PB-MS with conventional-size LC, microbore column (i.d. 1-2 mm) LC-PB-MS has also been developed. A well-optimised PB interface can provide a detection limit in the ng range for a full scan mode, and may be improved to pg for SIM analyses. 

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... 

LC-TSP-MS without tandem mass capabilities has only met with limited success for additive analysis in most laboratories. Thermospray ionisation was especially applied between 1987 and 1992 in combination with LC-MS for a wide variety of compound classes, e.g. dyes (Fig. 7.31). Thermospray, particle-beam and electrospray LC-MS were used for the analysis of 14 commercial azo and diazo dyes [594]. No significant problems were met in the LC-TSP-MS analysis of neutral and basic azo dyes [594,595], at variance with that of thermolabile sulfonated azo dyes [596,597], LC-TSP-MS has been used to elucidate the structure of Basic Red 14 [598]. The applications of LC-TSP-MS and LC-TSP-MS in dye analysis have been reviewed [599]. 

Electrospray has been successful for numerous azo dyes that are not ionic salts. Several anthraquinone dyes have been analysed by LC-ESI-MS [552]. Electrospray achieves the best sensitivity for compounds that are precharged in solution (e.g. ionic species or compounds that can be (de)protonated by pH adjustment). Consequently, LC-ESI-MS has focused on ionic dyes such as sulfonated azo dyes which have eluded analysis by particle-beam or thermospray LC-MS [594,617,618]. Techniques like LC-PB-MS and GC-MS, based on gas-phase ionisation, are not suitable for nonvolatile components such as sulfonated azo dyes. LC-TSP-MS on... 

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... 

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