Analytical methods general conclusions

The methods used must, ideally, permit sampling in a museum, preferably without moving the objects from the display area. The analytical methods should not be particularly time-consuming or expensive because of the volume of data generally required for valid conclusions. These fairly stringent requirements cannot be met in all cases, yet we have attempted to use them as a guide in our studies. 

Of all the systems which have been utilized for the analysis of pesticide residues, combined gas chromatography-mass spectrometry afiFords a particularly useful approach because positive identification of the components of a mixture can be made without prior separation at sensitivities compatible with the limited quantities of residues generally available. From the results of recent studies involving the application of this technique, it has been demonstrated that available residue analytical methods provide efficient isolation and adequate cleanup of extracts of human, animal, and environmental media in most cases to permit gas chromatographic-mass spectrometric analyses with maximum confidence. Additionally, it has been shown that this combined technique will conveniently provide definitive and conclusive confirmation of residue identity as well as characterization of residues and their metabolites of unknown structure. 

These studies employed refinements in analytical methods that allowed the accurate analysis of process flavors for the presence of PHAs. Previous efforts were hampered by the inherently low levels of PHAs in foods in general, and by the lack of a reliable and accurate analytical method. Since the studies reported here were conducted, further refinements have been achieved (e.g. Solyakov et al., 1999 Richling et al., 1999) that permit even more accurate assessments of the presence of PHAs in process flavors. However, the more recent refinements do not significantly change the conclusions from the studies reported here. 

The primary conclusion of the session on PAH analysis was that the results of older and analytical methods are generally confirmed by the present advanced analytical techniques. The older sampling methods, however, were recognized as deficient techniques in many aspects. 

A general conclusion that can be drawn from this short survey on the many attempts to develop analytical theories to describe the phase behavior of polymer melts, polymer solutions, and polymer blends is that this is a formidable problem, which is far from a fully satisfactory solution. To gauge the accuracy of any such approaches in a particular case one needs a comparison with computer simulations that can be based on exactly the same coarse-grained model on which the analytical theory is based. In fact, none of the approaches described above can fully take into account all details of chemical bonding and local chemical structure of such multicomponent polymer systems and, hence, when the theory based on a simplified model is directly compared to experiment, agreement between theory and experiment may be fortuitous (cancellation of errors made by use of both an inadequate model and an inaccurate theory). Similarly, if disagreement between theory and experiment occurs, one does not know whether this should be attributed to the inadequacy of the model, the lack of accuracy of the theoretical treatment of the model, or both. Only the simulation can yield numerically exact results (apart from statistical errors, which can be controlled, at least in principle) on exactly the same model, which forms the basis of the analytical theory. It is precisely this reason that has made computer simulation methods so popular in recent decades [58-64]. 

Figure 10-1 illustrates two statements that experience has shown to be generally valid for analytical results obtained by wet methods (1) The true value a and the mean x are different quantities, and one cannot be predicted from the other. (2) No conclusions about the frequency distribution can be drawn from a or from x. One more generalization applies to comparative x-ray methods, be they absorption (3.10) or emission (7.8) methods If the comparison is properly carried out, questions of accuracy will never arise properly includes the use of a... 

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

As a conclusion, it is important to state that the use of only one fault detection, isolation and diagnosis method is not suitable for real industrial implementation. Furthermore, a mixture of shallow and deep knowledge is generally available on the real processes and, in some cases, analytical models... 

If properly executed, the validation is essentially completed at the conclusion of method development. The experiments that provide confidence to the analytical chemist that the method is suitable are generally the same experiments that a method validation requires. 

---