Evaluations Following Biological Means

A separate class of experimental evaluation methods uses biological mechanisms. An artificial neural net (ANN) copies the process in the brain, especially its layered structure and its network of synapses. On a very basic level such a network can learn rules, for example, the relations between activity and component ratio or process parameters. An evolutionary strategy has been proposed by Miro-datos et al. [97] (see also Chapter 10 for related work). They combined a genetic algorithm with a knowledge-based system and added descriptors such as the catalyst pore size, the atomic or crystal ionic radius and electronegativity. This strategy enabled a reduction of the number of materials necessary for a study. 

Serra et al. [122] used an evolutionary strategy for the design of catalyst libraries to evaluate a synthesis route for styrene from toluene. 

During the investigations, the learning proceeded on two classes of catalysts defined as bad and good according an objective function, which gives more importance to the production of the target molecule styrene than to the consecutive reaction product ethylbenzene. 

---

Once the data are available for analyses, evaluation of the results follows. There are several criteria for determining a positive result, such as a concentration-related increase over the range tested and/or a reproducible increase at one or more concentrations in the number of revertant colonies per plate in at least one strain, with or without metabolic activation system. The concentration-related increase would be three times the mean concurrent vehicle control value for strains TA1535, TA1537, and TA1538 and two times the mean vehicle control value for TA98, TAIOO, and WPi uvrA. Biological relevance of the results should be considered first. Results achieved at levels of excessive cytotoxicity (50% or more) are discarded. 

In principle, the certification of RMs for microbiological parameters does not differ from the approach used by BCR for chemical parameters. They fall into the category of method-dependent CRMs certified for an activity. In fact, the microbes will behave differently from one type of method (in particular the culture medium) to another. For selective media the resuscitation rate of the microbes in the RM will change. Injured bacteria will have difficulties to form colonies on these media. This reflects the biological activity of the strain after stabilisation. As the method will strongly affect the result, it must be verified that the method was applied in a similar way by all participants. This means that accurate protocols have been prepared and tested beforehand in a feasibility study. The first step of the evaluation of the certification study will be to verify that the protocol was strictly followed. This protocol will be made available to the users of the CRM. 

---