Expert Flow Systems

It is noteworthy to mention that, from a practical point of view, operation of the flow system for catalytic determinations is the same as for determinations involving the attainment of chemical equilibria. In fact, all of the temporal requirements inherent to catalytic analytical methods are efficiently fulfilled by the flow analyser. 

Alternatively, flow analysers can be operated in an active manner, and each sample is handled under specific conditions. To this end, real-time modifications of the sample handling conditions according to a concentration-oriented feedback mechanism are achieved. As a rule, a prior assay is carried out and the analytical result is used to feed the software with information for real-time decisions. The need for in-line modification of the degree of sample dilution, sample replacement, activation of 

This idea was embodied in the IUPAC definition of automatic systems The use of combinations of mechanical and instrumental devices to replace, refine, extend, or supplement human effort and faculties in the performance of a given process, in which at least one major operation is controlled, without human intervention, by a feedback system [367]. The key point for an automatic system is therefore the incorporation of a feedback system, i.e. the combination of a sensing and a commanding device that can modify the performance of a given act [367[. In other words, the response of a sensing device is used for the real-time modification of system operation. These definitions also hold for flow analysis automatic analysers are expert flow systems (Fig. 8.26), often referred to as smart or intelligent flow systems. 

In view of the low costs of installation and operation, inherent flexibility, ease of operation and control, low consumption of reagents and short analysis times, as well as their compatibility with multi-commutation, most expert flow systems rely on unsegmented flow analysis. The 

FIGURE 8.26 Block diagram of a typical expert flow system. Fluid propulsion, sample handling, detection = units of the flow analyser (Chapter 6) S, C, 2R = sample, carrier, reagents solutions (inlet represented by the empty arrow) arrows = computer/unit interactions. For details, see text. 

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Rb Drugs (Rb efflux assay) FP (eventually FAAS) 170 25-750 mg L 1 Expert flow system/real-time tsp selection in accordance to the analyte concentration [130]... 

The degree of in-line sample dilution can be defined in real-time and this is a key benefit of expert flow systems (see 8.7). 

Zone sampling (see 7.2) can be exploited in some expert flow systems with LLE in order to improve their performance, as initially demonstrated by the determination of Ci—C5 n—mercaptans in gasoline [199] (see also 8.7). Another example is the determination of ammonium by exploiting ion pairing [200]. 

This innovation generally involves modifications to the operation of the sampler and random access reagent selection, and can be implemented in both segmented and unsegmented flow analysers. For unsegmented flow analysis, the spectrophotometric determination of zinc and phosphate in soil extracts [368] is a good example. Zinc was determined only when phosphate was present at concentrations above a threshold level. The number of determinations required was reduced by 30%. Analogously, an expert flow system was proposed for the turbidimetric determination of chloride and sulphate in natural waters [369]. Both methods were implemented in the same manifold, and the need for sulphate determination was dependent on the chloride concentration determined. 

In this context, expert flow systems are important tools for screening purposes, as they permit real-time sample classification [370]. It should be emphasised that ordinary flow analysers used with the objective of offline classification of samples in different categories cannot be considered as expert flow systems. 

Expert flow systems take advantage of iterative control devices which work in tandem and permit real-time alterations of the experimental parameters. They are designed to provide decisions for the real-time introduction of correction factors and, eventually, manifold self-optimisation. Enhanced system versatility and flexibility are also achieved. 

Titrimetric procedures have been carried out efficiently using expert flow systems because a different analytical signal can be obtained after every titrant addition. A feedback mechanism relying on these signals can then be exploited to modify the course of the titration in order to refine the end point search and improve the accuracy [400]. Fundamental aspects of the analytical potential, advantages/limitations and applications of the different types of flow titration (with or without expert flow systems) are presented in Section 8.6.2. 

Segmented flow analysers using a bubble gating flow cell (Fig. 5.4) for monitoring the sample zone without the need for mechanical removal of the air phase [405] can also be considered as examples of flow systems exploiting a feedback mechanism that are not expert flow systems. 

P.R. Fortes, M.A. Feres, E.A.G. Zagatto, An expert flow system involving in-line prior assay for turbidimetric determination of chloride and sulphate in natural waters, Talanta 77 (2008) 571. 

Major trends in the future growth of flow analysis are likely to include the evolution of instrument design (including miniaturisation and expert flow systems), the recognition of more flow-based standard methods, hyphenation with other detection systems and an impact on chemical measurements in new and emerging areas of science. 

Fully automated instrumentation will also allow a more systematic application of expert flow systems as discussed in Chapter 8. 

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