Defined by fractionation

Figure 33.9 shows the LD mass spectrum of the NMP-insoluble fraction of the sample, with maximum ion intensity at m/z 3000 and an upper mass limit of m/z 10,000. Table 33.3 lists the maximum intensity masses (m/z) and upper mass limits of the mass spectra of the whole sample, the maltene and asphaltene fractions, and several TLC fractions from each of them. It is clear that the Syncrude contains some material of relatively high mass that can only be defined by fractionation to isolate it from low-mass components. 

The description of a crystal structure always refers to the dimensions of the unit cell, and the atomic positions within this space are described using the concept of fractional coordinates. A point within a unit cell is defined by fractions along the basis vectors a, b and c, and is thus defined as xa, yb, zc). For example, the center of a unit cell is and the point (1,1,1) is equivalent to the origin. 

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