Chemical quadrupole mass spectrometer

It is very evident in Figure 3 that the chemical complexity of Hasteloy presents special problems for mass spectrometric analysis using a quadrupole mass spectrometer with low mass resolution. Molecular ions comprised of combinations of matrix and plasma atoms are formed in abundance and will obscure many elements... 

Reversed-phase high-performance liquid chromatography (HPLC) column 50 mm x 3.2-mm i.d. with Kromasil 5- um Gig packing High-performance liquid chromatograph coupled to a triple-quadrupole mass spectrometer with an atmospheric pressure chemical ionization (APCI) source Gel permeation chromatograph with a 60 mm x 25-mm i.d. column packed with Bio-Beads SX-3 (50-g)... 

As with all spectroscopic methods discussed previously, this method is best suited to measurement and elucidation of the characteristics of pure compounds. For this reason, MS is often used as a detector for gas chromatographs. The GC separates the mixture into pure compounds and the MS then analyzes each pure chemical as it exits the column. The most common MS for this application is the quadrupole mass spectrometer. For this reason, it is discussed in Chapters 14 and 15. 

Fig. 1.6 (A) Electron impact spectrum obtained on a single quadrupole mass spectrometer of a compound with Mr = 355. (B) Product ion spectrum after atmospheric pressure ionization obtained on a triple quadrupole instrument. Chemical ionization and atmospheric pressure ionization give in both cases protonated precursor ions, which is ideal for tandem mass spectrometry.

Highly exothermic chemical reactions can give ions as products. Such reactions are called chemi-ionization reactions. When one or more of the reactants are formed by pulsed photolysis, and the ion product(s) are time-resolved with a mass spectrometer, this comprises a FPTRMS experiment. The ions can be extracted by a biased pair of electrodes, one of which has an aperture through which ions pass to enter a quadrupole mass spectrometer. The time resolution of this experiment is superior to FPTRMS experiments between neutrals, since the ion velocities are set by the electrode bias voltage, and the thermal molecular velocity distribution limitation is no longer a factor. With modest electrode bias voltages, the detection time can be as short as 2 /is. 

Several researchers have combined the separating power of supercritical fluid chromatography (SFC) with more informative spectroscopic detectors. For example, Pinkston et. al. combined SFC with a quadrupole mass spectrometer operated in the chemical ionization mode to analyze poly(dimethylsiloxanes) and derivatized oligosaccharides (7). Fourier Transform infrared spectroscopy (FTIR) provides a nondestructive universal detector and can be interfaced to SFC. Taylor has successfully employed supercritical fluid extraction (SFE)/SFC with FTIR dectection to examine propellants (8). SFC was shown to be superior over conventional gas or liquid chromatographic methods. Furthermore, SFE was reported to have several advantages over conventional liquid solvent extraction (8). Griffiths has published several... 

Determination of MS/MS conditions using the MALDI ion source coupled to the triple-quadrupole mass spectrometer takes a different approach (Kovarik et al., 2003) which at present is not as easily automated. As mentioned earlier, some product ion spectra will contain additional fragment ions not related to the analyte due to isobaric matrix peaks. However, MS/MS conditions previously obtained by using an ESI-MS/MS system can be directly ported over to the MALDI triple-quadrupole mass spectrometer. These conditions provide the advantage of product ion selection for SRM of the analyte. In the typical high-throughput environment, individual methods for each chemical entity are not normally utilized. Rather, the semioptimized template-style methods referred to above are often used wherein a few values of collision energy are combined with the appropriate SRM and polarity. These methods are ported to the MALDI triple quadmpole mass spectrometer, and no further... 

The chemical ionization mass spectrum of cimetidine and the major fragmentation ions are presented in Figure 8 and Table 4. The spectrum was obtained using a Finnigan lYbdel 3200 quadrupole mass spectrometer fitted with a chemical ionization source. The sample, applied to the probe from an acetone solution, was introduced via the direct inlet system. Methane was used as the reactant gas. 

For abbreviation of analyte names see Sect. Abbreviations . ACN acetonitrile, APCI atmospheric pressure chemical ionization, dial, microdialysis samples, ESI electrospray ionization, FA formic acid, iso isocratic, IT ion trap, lin range linear range, MeOH methanol, MRM multiple reaction monitoring, MS full scan mass spectrometry, n.s. not specified, OAc acetate, QqQ triple quadrupole mass spectrometer, SIM selected ion monitoring, Solv HPLC solvent, SQ single quadrupole mass spectrometer, T temperature Ratios given as v/v... 

Some researchers have reported instrumental modifications to reduce chemical matrix effects, including a three-aperture interface [103,181] and removal of the ion optics [182]. These modifications appear to reduce the total ion current, and therefore, space-charge effects, before ions enter the quadrupole mass spectrometer. Modification of ion optic lens voltages and configurations may also reduce space-charge-induced chemical matrix effects [183-186]. 

The use of tandem mass spectrometers can eliminate the sample preparation steps and provide improved capabilities for MS analysis. One system, the triple quadrupole mass spectrometer, uses a combination of three quadrupoles, or mass analyzers, to ionize, separate, and analyze sample components with minimum sample preparation as shown in Figures 7 and 8. The sample components are ionized and separated according to their mass-to-charge ratio in the first quadrupole. This step corresponds to the GC step in GC/MS. In the second quadrupole these ions collide with an inert gas and fragment (chemical ionization). 

Gas-Chromatography Mass Spectral (GC-MS) Analyses. Several different studies were carried out. The main study was done using a Finnigan MAT 4500 series quadrupole mass spectrometer and a 60 m X 0.32 mm l.d. DB-1 bonded fused silica capillary GLC column. The column was programmed from 25-250°C at 4° per minute with an inlet pressure of 14 psi. Chemical ionization (Cl) mass spectra on some of the components were also obtained using a VG Micromass 70/70 mass spectrometer with Isobutane as the reactant gas. 

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