Mass spectrometer double-focussing

A novel HF-plasma SNMS instrument which can be combined with XPS has recently been developed [3.67]. Detection limits in the nmol/mol range have been achieved with a dedicated HF-plasma instrument attached to a double-focussing mass spectrometer [3.68]. 

In 1935 A.O. Nier designed a relatively simple but accurate mass spectrometer employing the principle of double focussing. The essential features are the same as described above but some improvements have been made which are ... 

MAT 731 double-focussing mass spectrometer, a combined EI/FI/FD/FAB ion source and an AMD Intectra direct introduction system, has been previously described in detail (12). The samples were heated linearly from 50 C to 750 C at a rate of 100 K/min. In general, 35 FI mass spectra were recorded in the m/z 50-900 mass range. 

Field desorption and electron impact ionization mass spectra were taken by using a Matsuda type double focussing spectrometer... 

A few years ago, we began a research program to develop methods of analysis which would involve the use of FAB and a high performance tandem mass spectrometer. The tandem instrument was the first triple sector mass spectrometer to be designed and built by a commercial instrument company (Kratos of Manchester, U.K.). The first mass spectrometer of the combination is a double focussing Kratos MS-50 which is coupled to a low resolution electrostatic analyzer, which serves as the second mass spectrometer U). This FAB MS-MS combination has been used to verify the structures of an unknown cyclic peptide (2), a new amino acid modified by diphtheria toxin (3), and an ornithine-containing lipid (4). A number of methods have also been worked out which rely on this instrumentation. They Include the structural determination of cyclic peptides (5), nucleosides and nucleotides (6), and unsaturated fatty acids (7) and the analysis of mixtures of both anionic (8) and cationic surfactants (9). 

Although there are many attractive features of Fourier transform mass spectrometry (FTMS), there are problems with current implementations. The FT mass spectrometer is still a relatively young instrument when compared to the double-focussing mass spectrometer, and comparisons of the spectrometers and their... 

Comparison with Sector Instruments. Modern double-focussing mass spectrometers have a long history of development, which was recently reviewed O) The instrument has evolved through a long series of complex and interweaving events beginning with the early experiments of J. J. Thomson (2) and the first mass spectrographs of... 

Belshaw, N.S., Freedman, P.A., O Nions, R.K., Frank, M., and Guo, Y. (1998) A new variable dispersion double-focussing plasma mass spectrometer with performance illustrated for lead-isotopes. Int. J. Mass Spec. Ion Process, 181, 51-58. 

Rates of decomposition of the molecular ions of aminotriazoline stereoisomers have been determined over the time range tens of picoseconds to microseconds using a blade emitter and a double-focussing mass spectrometer [399]. The predominant process at the shortest times was, in all cases, loss of molecular nitrogen. The stereoisomers decomposed at very different rates, which was interpreted in terms of differing rate coefficients, k(E), arising from different amounts of steric strain. 

The rate of loss of a methyl radical from the molecular ion of diethyl ether has been measured using a single-focussing mass spectrometer [42, 825]. The time resolution here was a few picoseconds. Loss of a methyl radical from the molecular ion of di-isopropyl ether has been investigated using a double-focussing instrument [743]. 

The rates of all the various decomposition pathways of the molecular ion of n-butyl acetate have been investigated using a double-focussing mass spectrometer [743]. There appears, however, to have been either an error in the calculation of times or the calculations are simply imprecise. The times reported appear to be too short, perhaps by something like a factor of 3. This being so, the agreement between these incorrect times and decomposition times for related ions [520] would not be significant. 

Charge exchange will suffer the same problems with intramolecular kinetic isotope effects as PIPECO if single-focussing mass spectrometers are used. Charge exchange with a double-focussing mass spectrometer should, however, allow determinations of intramolecular kinetic isotope effects. 

Double FocussmgMass Spectrometers. Two factors that limit the resolution of a single focussing mass spectrometer to a maximum of about 5000 are the... 

Figure 5. Resonance ionization spectra of the elements Re, Fe, Ni, and Mo. For each element the wavelength of the frequency-doubled dye output was scanned while focussing the mass spectrometer on the most abundant atomic ion of the element. Each wavelength dependent peak represents ion formation from a specific groTond state or metastable atomic energy level (ll).

Boyd, R. K., Porter, C. J. and Beynon, J. H. Linked-scan laws to detect fragmentations in the second field-free region of a double-focussing mass spectrometer. Int.. Mass Spectrom. Ion Phys. 44 199-214, 1982. 

In commercial instrumentation fairly low-cost quadrupole mass spectrometers and also expensive double-focussing sector field mass spectrometers are usually used (for a survey of mass spectrometers for analytical use, see Ref. [71]) and today new types of mass spectrometers such as time-of-flight mass spectrometers are being find utilized in plasma atomic spectrometry. 

A schematic representation of a double-focussing mass spectrometer is shown in Fig. 10.4. For historical reasons, this set-up is referred to as a reverse-geometry magnetic sector mass spectrometer, which means that the magnetic sector precedes the electric sector [1]. 

Linked scans, in which the magnetic and electric fields are scanned together, can be used to perform MS/MS experiments (product, precursor, and neutral loss) with a double focussing mass spectrometer. 

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