Analyzer cell

Mclver R T 1970 A trapped ion analyzer cell for ion cyclotron resonance spectroscopy Rev. Sc/. Instrum. 41 555-8... 

A Pt(s)[7(111) X (100)] crystal is positioned in front of a hole in one of the plates of the analyzer cell. Ions formed by electron impact are trapped in the analyzer cell and detected by FTMS. An exclmer laser, having a pulse width of 20 nsec, is used to desorb molecules from the Pt crystal. 

Figure 6 shows the sequence of events in a laser desorption FTMS experiment. First, a focused laser beam traverses the analyzer cell and strikes the crystal normal to the surface. Molecules desorbed by the thermal spike rapidly move away from the crystal and are ionized by an electron beam which passes through the cell parallel to the magnetic field and 3 cm in front of the crystal. 

Figure 4. Ions undergoing coherent cyclotron motion induce image currents in the plates of the FTMS analyzer cell. Reproduced with permission from Ref. 18. Copyright 1985, North-Holland Physics Publishing.

Figure 6. The sequence of events in a laser desorption FTMS experiment, (a) The laser beam enters the cell and strikes the crystal, (b) Some of the desorbed molecules are ionized by an electron beam, (c) Ions are trapped in the analyzer cell by the magnetic and electric fields, (d) Ions are accelerated by an RF pulse and the resulting coherent image current signal is detected. Reproduced with permission from Ref. 18. Copyright 1935, North-Holland Physics Publishing.

Figure 7b also illustrates the high detection sensitivity of the FTMS instrument. We calculate that the CO peak corresponds to approximately 5000 ions in the analyzer cell. In Figure 7a, the number of ions with m/z 43 was calculated to be approximately 20 million. A point to note is that In FTMS the sensitivity increases with resolution whereas it decreases with other mass spectroscopies. 

Dissimilarity and clustering methods only describe the compounds that are in the input set voids in diversity space are not obvious, and if compounds are added then the set must be re-analyzed. Cell-based partitioning methods address these problems by dividing descriptor space into cells, and then populating those cells with compounds [67, 68]. The library is chosen to contain representatives from each cell. The use of a partition-based method with BCUT descriptors [69] to design an NMR screening library has recently been described [70]. 

The proton transfer from multiply charged [cytochrome c] " (n = 7-9) to (/ )- and (5)-2-butylamine show a significant enantioselectivity." " Ions [cytochrome n = l-9) were produced by ESI and introduced into the analyzer cell of a FT-ICR containing an alkylamine, i.e., (/ )- and (5)-2-butyIamine, 1-propylamine, or tert-butylamine. Rate constants for the proton transfer are listed in Table 18. 

A variety of assays have been developed to quantify phagocytic activity. These include direct microscopic visualization (2,3), spectrophotometric evaluation of phagocytized paraffin droplets containing dye (4), scintillation counting of radiolabeled bacteria (5), fluorometric (6), and flow cytometric analysis of fluorescent particles (7-13). The flow cytometric assay offers the advantage of rapid analysis of thousands of cells and quantification of the internalized particle density for each analyzed cell. The assay may be performed with purified leukocyte preparations (7-13) or anficoagulated whole blood (14,15). 

---