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Figure 43. Non-linear map of pyrolysis mass spectra of 8 purified (•) and 3 incompletely purified (o) capsular polysaccharides of Neisseria meningitidis groups B, C, W-135 and Y. Groups B and C polysaccharides consist of linear chains of N-acetylneuraminic acid (sialic acid) with a (2-+S) and a (2->-9) glycosidic linkages, respectively. The W-135 and Y polysaccharides are composed of hexosyl-N-acetyl -neuraminic acid repeating units. The partially purified preparations B 11 and C 11 contain protein; the preparation C 11* contains in addition 1ipopolysaccharide contaminants. Note how the presence of all these differences in structure and composition results in characteristic shifts in the map: — shift due to the presence of hexose residues; -shift due to 0-acetyl substitution; ••• shift due to protein contaminants; — shift due to lipopolysaccharide contaminants.

described as a means of evaluating the full potential of Py-MS for detecting minute biochemical differences in highly defined cell and tissue samples (ref. 165).

In spite of the above severe limitations of Py-MS applications to practical clinical samples, the technique may eventually find applications in selected clinical problems, e.g. involving early detection and diagnosis, monitoring the course and extent of a disease or evaluating the effect of therapeutic measures. As noted by Laitinen (ref. 166): "The possibilities for diagnostic use'appear sufficiently promising to justify a research effort of considerable magnitude".

A similar "operational fingerprinting" approach to that used in microbiology has potential application in other medical areas, as demonstrated in Figures 42 and 43. Py-MS analysis of biochemical preparations such as bacterial antigens or virus preparations to be used in vaccines (see also Section 6.7) allows rapid testing of the overall biochemical composition of the sample (ref. 49, 63). Although this approach may not obviate the need for more specific tests, e.g. tests directly relating to the biological activity of the sample, it should provide manufacturers of complex biochemical preparations such as vaccines, drugs, beverages or foods with a unique tool for detecting the presence of unexpected contaminants or chemically altered components incurred during the manufacturing process.

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