Witness this army, of such mass and charge" Shakespeare, W.; Hamlet, 1601, Act IV, Scene 4, line 47. CCC 0277-7037/95/05/60359-52 LINKED-SCAN TECHNIQUES FOR MS/MS FIGURE 2. One-dimensional spectra for ions formed from decane, cxtracted from the complete two-dimensional MSiMS domain shown in Fig. I . Such one-dimensional spectra could be obtained by appropriate single scans, without obtaining all the information exhibited in thc full MS/MS domain. Full circles denote ions whose m i z values are fixed by the conditions of the experiment. and open circles denote ions whose m l i values are to be obtained from the appropriate one-dimensional scan. Reproduced from Ref. (2), by permission.appropriate kinds, without generating the complete MS/MS domain. This review is concerned with the experimental methods for generating such scans, using some common mass spectrometer designs. A more fundamental comment on maps like Fig. 1 concerns the significance of the observation. or not, of any particular reaction. Any such observation strictly refers only to the reaction timescale and other conditions pertinent to the particular apparatus in use. For example, the fact that the ion at m/z 43 was observed ( Fig. 2) to arise from the ion at m / z 85, as well as from the ion at m/z 71, does not necessarily imply that the direct (single-step) reaction (m/z 85+ 43) does occur. The only valid conclusion is that some ions of m/z 85, extracted from the ion source, can fragment to yield m/z 43, but whether or not all such events involve an intermediate at m/z 7 1 cannot be determined from these experiments alone. It is also important to note that the great majority of MS/MS experiments investigate fragmentation reactions (m, < m, , where m, is the molecular mass of species X ) . However, at the lower collision energies characteristic of quadrupole instruments, it is also possible to induce chemical reactions between the reactant ion and a suitable collision gas, such that m, > m,.
LINKED-SCAN TECHNIOUES FOR MS/MSFIGURE 3. Schematic representations of the action of (a) magnetic and (b) electric sector fields. In each case. 0 is the subject slit (length dimension perpcndicular 10 the plane of the paper. closeable in the plane). The angular spreads of the ion beam in the plane (which is perpendicular to the magnetic field direction, but contains the electric field lines) are a,,, and a,, respectively. (a) F,,? F , , F2, and F3 are the respective direction focus points for ions of mass m, and velocity u , [Eq. (28)]. mass (m, + 8m) and velocity u , , mass m R , and velocity [Eq. (28)] ( u , + Su), and mass (m,< + Sm) and velocity ( u , + 6u). Thus. the differences between F,, and F,. and between Fz and F2, represent the effective mass dispersion of the magnet. The differences between F,, and F2, and between F, and F; reflect the velocity dispersion. (b) F,, is the direction focus point for ions with any combination of m and u consistent with a kinetic energy ke) [Eq. (30)]. and F, is thc direction focus point [Eq. (30)] for ions with a kinetic...
