Natural products analysis complementary structural

The complementary structural information of both NMR spectroscopy and MS detection is particularly valuable for the analysis of closely related glycosidic natural products, where compounds of the same molecular mass (isobars, see Table 5.1.1), and even with identical MS/MS fragmentation patterns, frequently occur, as this example demonstrates. 

In conclusion, the FAB/tandem MS combination appears to offer some promise for structural studies on involatile natural products. Negative ionization and chemical ionization have also been employed to provide precursor ions for analysis and it appears that structural information complementary to that obtained by normal mass analysis is forthcoming for selected compounds. 

The role of antiwear additives in boundary lubrication has been mentioned briefly in the general presentation (Section 1). The way in which zinc dithio-phosphate (ZDDP) acts as an antiwear additive is almost certainly that of the elimination of the abrasive wear contribution of crystallized iron oxide species as a result of their tribochemical reactions with the additive molecules and/or various degradation products. The use of XAS and TEM/EELS together with complementary CEMS and AES represents a powerful analytical combination for the elucidation of the tribochemical reactions responsible for antiwear mechanisms. The first part of this section summarizes analytical results obtained with friction tests carried out in the ambient atmosphere. The second part describes some original results obtained with friction tests and in situ post mortem AES analysis in ultrahigh vacuum. In this way the intrinsic frictional properties of the solid reaction film itself, without the effect of the environment, and the ability of friction to modify the nature and the structure of the surface films are investigated. 

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