Multiple stage MS

The trapped ions possess characteristic oscillation frequencies. The stable motion of ions in the trap is assisted by the presence of a helium buffer gas (1 mtorr) to remove kinetic energies from ions by collisions. When a supplementary AC potential, corresponding to the frequency of a certain m/z ion, is applied to the end-cap electrode, ions are resonantly ejected from the trap. This method of resonance ejection is used to effectively extend the mass-to-charge ratio of the ion trap. Some other characteristic features of a 3-D ion trap include high sensitivity, high resolution with slow scan rate, and multiple-stage MS capability (see the section on tandem MS). In addition, it is inexpensive and small in size. As a result, a 3-D ion trap is widely used in LC/MS and LC/MS/MS applications. 

Limitations of GMF approaches are related to the data that comes in to the algorithms. Since tandem MS data is not as information rich as a set of multiple-stage MS spectra, it may not be possible to distinguish between two structures based on the one spectrum alone. In fact, it is often the case that supplemental evidence is required to make a confident assertion that structures have been assigned correctly. 

The ability to apply customized waveforms to the QIT, together with the fact that ions are trapped and therefore can be subjected to different treatment over a period of time, makes the QIT one of the most versatile of mass spectrometers, rivaled only by the ICR mass spectrometer. This is most strongly evident in tandem mass spectrometry (MS/MS and related techniques), which will be discussed separately. It should be noted here, however, that multiple stage MS/MS experiments (MS/MS/MS.. ., or MS ) experiments are readily performed in ion traps. 

For the determination of the sugar sequence of these saponins, an early prototype of a new ion trap mass spectrometer was tested. With this instrument, it has been possible to perform not only an MS/MS experiment, but a multiple stage MS/MS experiment (MS"). In MS ", it was possible to isolate and excite only one ion of interest and thus, to decrease the amount of consecutive reactions [10]. For example on the pentaglycosylated saponin 4, six stages of MS/MS were performed (MS ). The sugar sequence information was obtained by successive decomposition of the main ion, as shown in Fig. 6. 

Today numerous mass analyzers are available with completely different characteristics and field of use. Both single-stage MS and multiple-stage MS instruments can be purchased commercially nowadays. 

Multiple sclerosis (MS), 2624, 3426 Multiple-stage MS, 3316 Multiple-Step Engineering, 235 Multiple targets, 1295 Multistage mass spectrometry, 3239 Multi-target approach, 1257 Multitargeting phytochemicals, 2225 The Mu-1 opioid receptor subtype (OPRMl), 1377... 

In particular, to elucidate the structures of unknown compounds (not-target analysis), two sets of instruments are suitable. The first set concerns low resolution instruments such as QqQ or IT or QqLIT, from which information about the product ion MS/MS spectra can be obtained. The ability to generate detailed fragment ion data is a desired instrumental feature for structure determination of unknowns. The product ion scan (MS scan) with a QqQ mass spectrometer (Weiss et al. 2009) and the multiple-stage MS scan (MS scan) (Ikatajamaa et al. 2006 Smith et al. 2006) with a tridimensional IT (3D IT) mass spectrometer are two of the most common techniques used in LC/MS analysis for generating fragment ions from small molecules. 

Chevallier, C., Laprevote, O., Bignon, J., Debitus, C Guenard, D and Sevenet, T. (2004) Isolation of cytotoxic chondropsins, macrohde lactams from the New-Caledonian marine sponge Psammoclemma sp, and electrospray ion trap multiple stage MS study of these macrohdes. Nat, Prod, Res., 18, 479-484. 

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