Glycerol, as matrix

TTX is dissolved in 0.05 M acetic acid at a concentration of approximately 10 pg/pL. One microlitre each of this TTX solution and glycerol as matrix are placed on the sample stage of the mass spectrometer, mixed well, and introduced into the ion chamber of the spectrometer. Both positive and negative mass spectra of TTX are then measured. ... 

Glyceraldehyde-phosphate dehydrogenase arsenate and, 44 193-194 Glycerol, as matrix liquid, 28 5 Glyceiol-3-phosphate dehydrogenase, 44 206, 207... 

IR-MALDl enables comparably soft desorption processes and is, therefore, more appropriate for noncovalent complex analysis than UV-MALDl. This is reflected by the successful detection of intact double-stranded DNA as well as enzyme-oligosaccharide complexes in combination with glycerol as matrix which were not detectable or underwent significant fragmentation when UV-MALDI was employed [126, 127]. 

Dreisewerd and coworkers [21] performed an interesting study where native milk oligosaccharides were characterized by IR MALDl MS using glycerol as matrix. This is illustrated in Figure 18.2. The limit of detection for the MS analysis was about lOpmol of the individual oligosaccharides spotted for chromatography. 

Barber et al. introduced FAB in 1981. In this technique, bombardment of a liquid target surface by a beam of fast atoms such as xenon or argon, causes the continuous desorption of ions that are characteristic of the liquid. In a typical FAB spectrum, the analyte ion is usually formed as protonated or cationized ions in positive FAB, and deprotonated ions in negative FAB mode. A few fragmented ions may also be formed. The spectrum usually contains peaks from the matrix, such as protonated matrix clusters of glycerol if it is used as the matrix solvent. FAB utilizes a liquid matrix such as glycerol. The matrix is used to enhance sensitivity and ion current stability. 

This is a very widely used determination, but suffers from the drawback of matrix effects, for instance if the wine contains atypical concentrations of glycerol, as was first reported by Bouvier (1986). 

Gegiou et found only a very slight viscosity effect, both in the n-Ti and in the jt-jc absorption bands on the isomerization quantum yield. They used glycerol as a viscous solvent, but the result may also be transferred to polymer matrices. In solid matrices, several photoisomerization modes are observed (see the preceding section on the influence of temperature), A com parison between azobenzene isomerization in liquid methylmethacrylate and the slow mode in poly (methylmethacrylate) showed that the difference in quantum yields on Si (0.17) and S2 excitation (0.03) is retained in the solid matrix. The fast process is not observed in n —> n excitation. These data are important in relation to the use of the azobenzene isomerization method for the determination of the free volume in a polymer. 

In a continuous-flow fast-atom bombardment (Cf-FAB) interface, typically a 5-15 pl/min liquid stream, mixed with 5% glycerol as FAB matrix, flows through a narrow-bore fused-sihca capillary towards either a stainless-steel frit or a (gold-plated) FAB target. At the target or frit, a uniform liquid film is formed due to a subtle balance between solvent evaporation and solvent dehvery. Ions are generated by bombardment of the liquid film by fast atoms or ions, common to FAB. The Cf-FAB interface for LC-MS have been reviewed [37-38]. 

Direct inlet probe FAB-MS is an important tool in the analysis of compounds that are thermolabile and/or lack volatility [102]. Lack of sensitivity was initially a limiting factor but detection limits have been enhanced 10-100 fold, because of reduced suppression effects [103], with the use of a dynamic system in which the HPLC effluent is passed continuously into the ion source of the MS [104,105]. In the case of a frit-FAB HPLC interface, which is available commercially, reverse phase HPLC mobile phase, containing 1% glycerol as a matrix, is introduced into the ion source via a steel frit. The sample and matrix are then ionised on the inner surface of the frit with a beam of accelerated xenon atoms (Fig. 9). The optimum rate at which the HPLC mobile phase can be introduced into the ion source is 5 p.1 min and this necessitates the use of a reliable splitter when a conventional 2-5 mm bore HPLC column is used. Although a commercial post-column splitter is available, it is of limited value in the analysis of traee quantities of compounds. 

Organophosphonium salts are a general class of compounds which are difficult to analyse via conventional EI-MS Thus several reports have appeared in the literature which describe the use of alternative ionization methods to analyse this important class of compounds " Early studies, which centered around the use of field desorption (FD), demonstrated that the intact phosphonium ion is often the most abundant ion. A comparison was made between the use of FD and FAB as ionization methods for the analysis of the diphosphonium salt FD produces high abundances of the intact phosphonium ions [M - Br ] and [M - 2Br ], whereas these ions are only minor peaks in the FAB mass spectrum using glycerol as the matrix. Instead, the fragment ion 35 is the base peak in the FAB spectrum. 

Fast Aloin Bombariiment (FAB-MS). This was applied to Study the lactonization of HIL to ADF FAB-MS was performed on a Finnigan MAT 8430 double focusing mass spectrometer. FAB ionisation was carried out with a saddle-field atom gun (Ion Tech. Teddington, UK) which was operated at 2 raA and 7-8 kV with xenon. Glycerol was used as matrix. The positive ions at m/z 130 (protonated molecular ion of ADF) and 148 (protonated molecular ion of HIL) were recorded. 

Figure 2.7. Positive-ion FAB mass spectrum of Tyr-Gly-Gly-Phe-Met-Arg-Gly-Leu acquired using glycerol as the matrix.

Figure 5.4 IR-MALDI mass spectrum of large DNA analyzed from glycerol as a matrix. The spectrum depicts single-stranded DNA molecules of length up to 1.4 kb generated from restriction-digested plasmid DNA purified by ethanol precipitation. The...

---