Benzene mass spectral peaks

A mass spectrum is a plot or table of the mass-to-charge ratio, m/z, of detected ions vs. their relative abundance (relative concentration). A typical mass spectral plot for a small organic molecule, benzene, is presented in Fig. 10.1. The m/z values are plotted on the x-axis relative abundance is plotted on the y-axis. The most abundant peak in the spectmm is called the base peak. The base peak is assigned an abundance of 100% and the other peak heights are plotted as percentages of that base peak. A tabular form of benzene mass spectral data is given in Table 10.1. The tabular data have the advantage that very low abundance ions can be listed, such as the ions at m/z = 64 and 80 which are too small to be seen on the normalized plot. 

Alkyl benzene components in sample 7 were not represented in the canonical variate space. Mass spectral peaks corresponding to indane/tetralins in samples 8 and 9 were found by CMR to contain indanes, and anthracene/phenanthrene mass spectral molecular ions were found to be predominantly phenanthrene. 

For all the samples, the peak areas of the chromatograms were integrated and compared with an external calibration mixture of n-alkanes. Identifications were confirmed from GLC-mass spectral data. Virtually no unsaturates were evident in the mixture, but a small amount of alkyl-substituted benzenes was apparent at short retention times. Quantitative data for two coal liquefaction cmdes, a shale oil cmde, a Louisiana-Mississippi sweet petroleum cmde (LMS) and a mixed petroleum cmde (Alaskan, Ganadian, Galifomian, Iranian, Arabian, and LMS) are shown in Table I. These studies indicated that petroleum and shale cmdes have... 

When the monomer ratio in a copolymer increases, the contribution to the pyrolysate also increases. However, the yield of different pyrolysis products depends on the nature of the polymer. In addition to quantitative information, as shown in Chapter 4, structural information can be obtained from pyrolysate. One example in this direction is that of a poly(ethylene-co-methyl acrylate), CAS 25103-74-6, (with butylated hydroxyethyl-benzene inhibitor). A sample with 21.5% wt. methyl acrylate (MAc), with M = 79,000 and Mn = 15,000, pyrolyzed at 600° C in He with the separation on a Carbowax column generates the upper trace of the two pyrograms shown in Figure 6.1.11. The lower trace, displayed for comparison, is that of polyethylene. The peak identification for the pyrogram of poly(ethylene-co-methyl acrylate), with 21.5% wt. methyl acrylate, shown in Figure 6.1.11 was done using mass spectral library searches only, and Is given in Table 6.1.7. 

The current mass spectral libraries (NIST 2002, Wiley 7) do not contain the spectra of these compounds, and therefore they were not identifiable by the MS library searches. The use of mass spectrum fragments can be of help in these situations. One example is the tentative identification for the peak with retention time of 75.48 min. (from Figure 6.9.2) as 4-methyl-1 - 1 -methyl-1 -[2-methyl-5-(methylethyl)cyclohexyl]ethyl benzene. The fragment assignments for the ions seen in the mass spectrum are shown in Figure 6.9.3. 

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