Screening methods questions

The unequivocal recognition or exclusion of particular substances in question is of especial importance for such screening methods. As far as the chemist is concerned this can involve a deliberate search for substances with particular functional groups particular questions that might require answering might include the following ... 

Table 2.3 gives one way for an existing facility to get started toward successfully managing chemical reactivity hazards. This assumes you already have an idea as to what chemical reactivity hazards must be addressed by the management system, such as by answering the questions in the Preliminary Screening Method of Chapter 3. 

You may find the worked examples in Chapter 5 helpful for seeing how the Preliminary Screening Method is used and how the results are documented for a few typical situations. Each of the twelve questions in the screening method is explained in turn in the remainder of this chapter, with examples and other considerations. 

A review of material safety data and standard references for the ingredients may result in answering Questions 7 through 11 as shown in Table 5.5. Two of the ingredients, aluminum powder and sodium hydrosulfite, are known to be reactive chemicals, so a chemical reactivity hazard is obviously present. At this point, the Preliminary Screening Method would point the user to the information in Chapter 4, for identifying and managing chemical reactivity hazards. 

An important question that needs to be addressed in any screening study is the determination of whether or not the ligand is non-covalently bound to the active site of the target protein. A number of simple GPC spin column ESI-MS screening methods have been developed to answer this question. These methods include the use of mutated proteins where the active site has been modified, GPC spin column/ESI-MS coupled with NMR (GPC spin column/MS/NMR) and displacement of known binders. Titration experiments with molar excesses of ligand to protein (described below in Section 2.3.3.2.4) can also be used to determine whether single or multiple binding sites are available in the protein. 

While field screening usually appears to be an excellent way to save time and money, we must be cautious in its application. In particular, the following questions must be answered before a screening method is selected for field use ... 

In answering these questions, we must keep in mind that field screening methods produce mostly semiquantitative data that are not acceptable for confirmation sampling or site closure and that the screening method detection limits may not be sufficiently low for comparisons to the action levels. 

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