Particle beam ionization

Electron impact ionization, also known as particle beam ionization, has been applied to the online determination of steroids such as hydrocortisone, cortisone, prednisolone and prednisone. Polymer additives such as NC-4, Irga-nox 1076,1-octadecanol and Naugard -XL were identified and quantitated online by electron impact and, separately, by atmospheric pressure chemical ionization methods.78... 

Particle beam ionization, bquid chromatography, 4 625 Particle board bonding, phenolic resins in, 18 790... 

In recent decades the hyphenated technique, HPLC-MS, also become the method of preference in HPLC practice. Various techniques have been developed and applied for MS detection such as thermo-spray interface, atmospheric ionization (API), electrospray or ionspray ionization (ESI or ISI), and particle beam ionization. 

The commonly used interfaces are the electrospray ionization (ESI) source, thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), and particle beam ionization. The choice depends largely on the polarity and thermal stability of the analyte. Electrospray ionization is preferred for polar and ionic and veiy large molecules such as proteins and peptides. Atmospheric pressure... 

However, there are some reports available where particle beam ionization methods such as FAB (fast atom bombardment) were used [20] 2,3,4,5-bis-O-(methylethylidene)-P-D-fructopyranose as well as its sulfamate and the corresponding carbamate were investigated by Caldwell and coworkers [20] using an indirect approach, that is, a microtransfer method to isolate the carbohydrates of interest from the TLC plate prior to FAB MS analysis. The carbohydrates of interest could be separated by using cyclohexane and 2-propanol (5 1, v/v). 

Most notably, LC-MS is widely used for characterization and quantitation of nerve agents and hydrolysis products [60, 72-76]. After LC separation, several ionization techniques have been investigated for the detection of nerve agents, including early studies involving particle beam ionization (PBI), thermospray (TS) and continuous flow fast atom bombardment (FAB) [77-79]. Modern applications today have evolved from using TS and FAB techniques to the use of electrospray ionization (ESI), atmospheric pressure ionization (API) and atmospheric pressure chemical ionization (APCI). 

PAA Phenylarsinic acid 2-PAMCl 2-Parlidoxime chloride PAO phenylarsinic oxide PBI Particle Beam Ionization PDMS Poly(dimethylsiloxane)... 

The particle beam — after linear passage from the evacuation chamber nozzle, through the first and second skimmers, and into the end of the ion source — finally passes through a heated grid immediately before ionization. The heated grid has the effect of breaking up most of the residual small clusters, so residual solvent evaporates and a beam of solute molecules enters the ionization chamber. 

The nebulization and evaporation processes used for the particle-beam interface have closely similar parallels with atmospheric-pressure ionization (API), thermospray (TS), plasmaspray (PS), and electrospray (ES) combined inlet/ionization systems (see Chapters 8, 9, and 11). In all of these systems, a stream of liquid, usually but not necessarily from an HPLC column, is first nebulized... 

This method is still in use but is not described in this book because it has been superseded by more recent developments, such as particle beam and electrospray. These newer techniques have no moving parts, are quite robust, and can handle a wide variety of compound types. Chapters 8 through 13 describe these newer ionization techniques, including electrospray, atmospheric pressure ionization, plasmaspray, thermospray, dynamic fast-atom bombardment (FAB), and particle beam. 

It is worth noting that some of these methods are both an inlet system to the mass spectrometer and an ion source at the same time and are not used with conventional ion sources. Thus, with electrospray, the process of removing the liquid phase from the column eluant also produces ions of any emerging mixture components, and these are passed straight to the mass spectrometer analyzer no separate ion source is needed. The particle beam method is different in that the liquid phase is removed, and any residual mixture components are passed into a conventional ion source (often electron ionization). 

A stream of a liquid solution can be broken up into a spray of fine drops from which, under the action of aligned nozzles (skimmers) and vacuum regions, the solvent is removed to leave a beam of solute molecules, ready for ionization. The collimation of the initial spray into a linearly directed assembly of droplets, which become clusters and then single molecules, gives rise to the term particle beam interface. 

Fig. I. Experimental setup the clusters are emitted from the cluster condensation cell, passing as a particle beam through a differential pumping stage into the focus of a time-of-flight mass spectrometer, where they are ionized by a laser pulse.

El may be used with the moving-belt and particle-beam interfaces. Cl with the moving-belt, particle-beam and direct-liquid-introduction interfaces, and FAB with the continuous-flow FAB interface. A brief description of these ionization methods will be provided here but for further details the book by Ashcroft [8] is recommended. 

The range of compounds from which electron ionization spectra may be obtained using the particle-beam interface is, like the moving-belt interface, extended when compared to using more conventional methods of introduction, e.g. the solids probe, or via a GC. It is therefore not unusual for specffa obtained using this type of interface not to be found in commercial libraries of mass spectra. 

The particle-beam interface has been developed primarily to provide El spectra from HPLC eluates but may be combined with other ionization techniques such as CL If quantitative studies are being undertaken, a detailed study of experimental conditions should be undertaken. Isotope-dilution methodology is advocated for the most accurate results. 

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... 

Figure 7.28 Typical particle-beam interface. After Ashcroft [524]. From A.E. Ashcroft, Ionization Methods of Organic Mass Spectrometry, The Royal Society of Chemistry, Cambridge (1997). Reproduced by permission of The Royal Society of Chemistry...

Based on a new technology, particle beam enhanced liquid chromatography-mass spectrometry expands a chemist s ability to analyse a vast variety of substances. Electron impact spectra from the system are reproducible and can be searched against standard or custom libraries for positive compound identification. Chemical ionization spectra can also be produced. Simplicity is a key feature. A simple adjustment to the particle beam interface is all it takes. 

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