Liquid SIMS technique

The recent use of liquid matrices in SIMS has led to several significant accomplishments, particularly for the analysis of biomolecules by FAB mass spectrometry [101]. In the FAB/liquid SIMS technique, the analyte is dissolved in a liquid matrix, such as glycerol, at some optimum concentration in order to provide a surface which, during particle bombardment, is constantly replenished with sample molecules that diffuse from the bulk to the surface. The mobility of the sample molecules in the liquid matrix is an important property of this type of matrix. 

With the successful implementation of differentially-pumped external ion sources, FTMS is rapidly becoming a routine mass spectrometric technique. Medium-pressure interfaces for the coupling of GC, LC, FAB, and liquid SIMS into the external ionizer are currently under development, and should become available in the near future. 

The use of ion beams precluded the use of the term FAB and the family of techniques became known as liquid SIMS. 

For this in situ identification method especially FAB (Fast Atom Bombardment), Liquid SIMS (Secondary-Ion MS), or laser desorption are employed as ionization techniques (49,50). The analytes are sputtered from the TLC foil (Fig. 26 (51)), or the TLC plate is placed on a movable table. More details are described in Chapter 9, Thin Layer Chromatography Coupled with Mass Spectrometry. 

Colton has described FAB as a method that provides the molecular results of static SIMS under the high-flux conditions of dynamic SIMS. It is now understood that the important feature of this technique is the liquid matrix, and not the neutral beam. Thus, the technique is more appropriately described as liquid SIMS. The liquid... 

Fast atom bombardment, liquid-SIMS (secondary ion mass spectrometry), electrospray (ESI), and matrix assisted laser desorption (MALDI) ionization modes have been applied successfully for the investigations of biomolecules.However, ESI and MALDI are the two most frequently adopted techniques for investigations of biopolymersDetails involving the principles and application of all of these techniques can be found elsewhere. The samples may be introduced either directly or after liquid chromatographic separation. All of the above techniques, with the exception of MALDI, have been adopted for the LC/MS experiments. " Although most of the reported LC/MS investigations involved the electrospray ionization of the molecules, continuous flow-FAB ionization techniques have also been found useful. 

Nevertheless, in applications relevant for electrocatalysis and reactions that occur at solid-liquid interfaces, it has been essential to develop a methodology that can provide detailed insight into the surface and near-surface stmcture during the course of reaction. For that purpose, the in sim SXS diffraction technique, depicted in... 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

LD), in which flash vaporisation of the sample is induced, may be applied. Other techniques which permit detection of less-volatile chemical species are FD (with simultaneous desorption/ionisation of molecules), FAB (with the sample dissolved (dispersed) in a suitable liquid) and SIMS (based on bombardment of a solid surface with high-energy ions). LD-FUCR-MS is superior to FAB-MS for polymer/additive identification because it gives molecular ion fragmentation [83],... 

As evident from Scheme 7.13, most modern ionisation techniques have been used for TLC-MS, and no single ionisation method is used exclusively with TLC-MS. Various ionisation methods may be applied that avoid the need to evaporate the sample into an El or Cl source these are based in particular on sputtering (FAB, SIMS) or laser desorption. Several sputtering methods of ionisation do not require the use of a liquid matrix, e.g. TLC-SIMS [797], Recent developments include the use of matrix-assisted laser desorption ionisation (MALDI) and surface-assisted laser desorption ionisation (SALDI). It is obvious that TLC-MS is complemented with TLC-MS11 [800] and TLC-HRMS techniques. Table 7.82 lists the general characteristics of TLC-MS. 

Imaging SIMS. Steeds et al. (1999) included this technique in their study of the distribution of boron introduced into diamond, where it is a well-established dopant that controls the electrical conductivity. SIMS was performed with a field-emission liquid gallium ion source interfaced to a magnetic sector mass spectrometer capable of about 0.1 pm spatial resolution. 

The combination of different analytical techniques offers the possibility for a complete characterization of building materials impregnated with liquid alkyl-alkoxysilanes RSi(OC2H5)3. The results derived from IR, NMR and SIMS spectra can be summarized in the schematic layer structure shown in Figure 5. 

Nevertheless, the introduction of time-of-flight (ToF) analysers for SIMS analyses at the beginning of the 1980s, as well as the recent development of liquid ion sources delivering cluster projectiles now permit the analysis of organic materials with high sensitivity and selectivity. Moreover, thanks to its excellent lateral resolution (in the order of micrometres), and its minimal sample preparation, ToF-SIMS has become the reference technique for chemical imaging by mass spectrometry. 

Dye identification is of great interest in textile studies. The classical procedure requires a hydrolysis step and other extraction techniques, followed by identification of the individual compounds present after separation by a chromatographic technique, e.g. high-performance liquid chromatography [Novotna et al. 1999, Szostek et al. 2003]. However, ToF-SIMS can be an alternative method, avoiding the phase of extraction which is always a time consuming and delicate step because of the possible destruction of the molecular structure of the sample [Ferreira et al. 2002]. The development of ToF-SIMS for dye detection has been reported in different studies. 

Mass spectrometry is traditionally a gas phase technique for the analysis of relatively volatile samples. Effluents from gas chromatographs are already in a suitable form and other readily vaporized samples could be fairly easily accommodated. However the coupling of mass spectrometry to liquid streams, e.g. HPLC and capillary electrophoresis, posed a new problem and several different methods are now in use. These include the spray methods mentioned below and bombarding with atoms (fast atom bombardment, FAB) or ions (secondary-ion mass spectrometry, SIMS). The part of the instrument in which ionization of the neutral molecules occurs is called the ion source. The commonest method of... 

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