6.6.1. Subtraction techniques
In its simplest form the question regarding the biochemical nature of an observed difference between two classes of pyrolysis mass spectra can be answered by subtraction. Calculation of average spectra for each class may improve the reliability of the procedure. Figure 32 shows the results of subtracting the average spectra of the non-dystrophic muscle biopsy samples from the dystrophic samples. The positive component of the difference spectrum shows a prominent ion series at m/z 67, 81, 95 and 109, indicating the presence of pyrroles. In biomaterials, marked pyrrole series are often derived from porphyrins (ref. 136) or from pro!ine-containing compounds (ref. 137). The latter possibility immediately suggests the presence of relatively large amounts of collagen, a protein unusually rich in proline (12%) and
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