Relative mass intensities

Table II. Relative mass intensities evolved from the 1 4 chloride complex at three temperatures during thermal decomposition in the mass spectrometer. Nominal temperature values are given.

Fig 2 Mass spectrum of carbon dioxide. Relative peak intensities are plotted against mje. 

FIGURE B.6 The mass spectrum of neon. The locations of the peaks tell us the relative masses of the atoms, and the intensities tell us the relative numbers of atoms having each mass. 

These features characterize the distribution of the peaks across the mass range. Feature xDUST indicates the relative amount of peak intensities in the low mass range up to mass 78. Feature xBAse is the base peak intensity in percentage of the total sum of the peak intensities, /all- The relative peak intensities at even masses are described by feature xEVen-... 

The mass spectrum shows the molecular ion of the monomer only the CeF5S+ ion is also present in relatively high intensity. These findings suggest that the S—N bond in the polymeric C9F5SNCO is very weak and consequently the compound depolymerizes quite readily. 

A further result of this analysis, as shown in Fig. 4, is that while the relative spectral intensities are determined by the individual site f-factors, the temperature dependence of all the sub-spectra together in the temperature range studied is determined by the motion of the center of mass of the whole Auj, cluster. This can be seen by the uniform decrease of the total intensity with increasing temperature, without any visible change in the general shape of the spectrum. In effect, this means that the f-factors for the individual sites must be multiplied by an f-factor due to the motion of the whole particle [24]. See also Refs. [95,96,97], where this concept was originally developed. The use of such an inter-cluster f-factor, in addition to the usual intra-cluster f-factor, also resolved the problem of the apparent deficiency in the total f-factor at 1.25 K when compared to bulk gold. 

The use of MALDI-MS for the measurement of low molecular mass compounds is widely accepted now [61], but quantification remains problematic. The main problem is the inhomogeneous distribution of the analytes within the matrix [62]. This leads to different amounts of ions and therefore to different signal intensities at various locations of a sample spot. The simplest and most effective way to overcome this problem is the use of an appropriate internal standard [63]. The use of deuterated compounds with a high molecular similarity to the analyte as internal standards leads to a linear correlation between relative signal intensities and relative amount of the compound to be quantified (Fig. 4b) [64]. Using this approach it is possible to quantitate substrates and products of enzyme catalyzed reactions. Two examples were shown recently by Kang and coworkers [64, 65]. The first was a lipase catalyzed reaction which produces 2-methoxy-N-[(lR)-l-phenylethyl]-acetamide (MET) using rac-a-... 

Fig. 5. Courses of predicted and off-line measured cell dry mass concentration and NAD(P)H-dependent relative fluorescence intensity during a high-cell-density cultivation of...

Figure 13. Cartesian [center-of-mass (CM)] contour diagrams for NH+ produced from reaction of N+ with H2. Numbers indicate relative product intensity corresponding to each contour. Direction of N+ reactant beam is 0° in center-of-mass system. For clarity, beam profiles have been displaced from their true positions (located by dots and 0°). Tip of velocity vector of center of mass with respect to laboratory system is located at origin of coordinate system (+). Scale for production velocities in center-of-mass system is shown at bottom left of each diagram (a) reactant N+ ions formed by impact of 160-eV electrons on N2 two components can be discerned, one approximately symmetric about the center of mass and the other ascribed to N+(IZ3), forward scattered with its maximum intensity near spectator stripping velocity (b) ground-state N+(3/>) reactant ions formed in a microwave discharge in N2. Only one feature is apparent—contours are nearly symmetric about center-of-mass velocity.12 ...

The mass spectra at scan numbers 30-35, 80-85, and 140-145 in RIC profiles of (S)-1,1 -bi-2-naphthol-t/2 (MT 288) and (R)-1,1 -bi-2-naphthol-t/2 (MT 286) with tris(5-fluoro-2-methylphenylcarbamate) are shown in Figure 4, where differences in the ratios of m/z 288 to m/z 286 are clearly detected. A plot of the ratio of m/z 288 to 286 (the mean value of six scan) versus the scan number is also shown in Figure 4. Initially, the relative peak intensity of m/z 286 was larger than that of m/z 288, which increased as the sample temperature was raised. These results indicate that the molecule of Mr 288 [(5)-1,1 -bi-2-naphthol-(72] vaporizes more slowly at higher temperature than the molecule of Mr 286 [(/ )-l,l -bi-2-naphthol-d2]. When a mixture of (relative intensity of m/z 286 to 288 (the reciprocal of the ratio in Fig. 4) showed the same tendency. 

When optically inactive polystyrene was used as adsorbent, no difference in the relative peak intensity at m/z 288 to 286 was detected. Moreover, in the resolution of (RS)-1,1 -bi-2-naphthol and (if5)-l,l,-bi-2-naphthol-rf2 on the CSP, no isotope effect was observed. These findings indicate that the difference in EI-MS spectra is due to the difference in desorption between the enantiomers from the chiral adsorbent tris(5-f uoro-2-methylphenylcarbamate). This method can be used to discriminate the chirality of other enantiomers of small molecules if they show peaks in their EI-MS spectra in the presence of chiral polymers. Similar chiral recognition was detected by negative ion fast-atom bombardment mass spectrometry [34],... 

Tobe and coworkers have extended their work to the pyridine-based cyclophynes 17 and 18 in efforts to detect the incorporation of heteroatoms into the fullerene structure [39]. Similar to the behaviour of the hydrocarbon 16, heterocyclic 17 and 18 show the successive loss of indane units and hydrogen under the conditions of LD mass spectrometry (negative ion mode) culminating in the observation in both cases of the formation of the anion C5gN2. The relative low intensity of the diazafullerene anion observed can be attributed to the kinetic and thermodynamic instability of the heterocage formed. 

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