Inhibitors continued principles

Fig. 5.1 Principle of MS-based enzyme assays. Enzyme (E) molecules react with the substrate (S) to form an enzyme-substrate complex (ES), leading, for example, to a subsequent cleavage into two products Pi and P2. Pi and P2 are monitored continuously by ESI-MS. The injection of an inhibitor, I, results in the temporary formation of an inactive enzyme-inhibitor (El) complex, resulting in a reduction of Pi and P2 and negative peaks in the corresponding mass traces.

The precise mechanism resppnsible for the passivity conferred on metals by anodic inhibitors, such as chromate, is not known. While some early workers thought that a protective salt film (e.g., chromate) was formed, this view is not generally applicable, since passivity can occur in a system where the salt film would be freely soluble (e.g., iron in nitric acid). It is, however, generally accepted that passivity is associated with the formation of a protective film, and current views ascribe the action of anodic inhibitors either to adsorption at anodic sites or to continuous repair of the protective film. The former view has received attention in recent publications by Cartledge ), while the latter is favored by Evans (2). However, work on aluminum has suggested that true passivity is associated with the crystal structure of the film, which in turn determines its stability. This principle has recently been introduced by one of the authors (3) and is developed below into a general theory of passivity. 

The corrosion inhibitors appear to possess properties that impart to metals resistance to attack by a variety of corrosive agents, such as brines, weak inorganic acids, organic acids, COj, HjS, etc. The method of carrying out this process is relatively simple in principle the corrosion preventive reagent is dissolved in the liquid corrosive medium in small amounts and is thus kept in contact with the metal surface to be protected. Alternatively, the corrosion inhibitor may be applied first to the metal surface, either as it is or as a solution in some carrier liquid or paste. Continuous application, as in the corrosive solution, is the preferred method, however. The concentration of the corrosion inhibitors varies widely, but the preferable concentrations are 15-250 ppm. 

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