Flow-through sensors continuous configurations

Bio)chemical sensors can be used in both the batch and the continuous mode. While this is also true of probe-type sensors, flow-through sensors can only be used in a continuous regime coupled on-line to a continuous-flow configuration. 

Compatibility between sensors and automatic and automated analytical systems is crucial as it allows two Analytical Chemistry trends to be combined (see Fig. 1.1). Probe-type and planar sensors can be used in automated batch systems including robot stations, as well as in continuous (mixed in-line/on-line) systems. On the other hand, flow-through sensors are only compatible with continuous configurations. 

Figure 2.12 — Continuous configurations coupled on-line to flow-through sensors involving transient immobilization of the analyte (A) contained in the sample (S). P pump. C carrier. RC regenerating carrier. R reagent. IV injection valve. SV switching valve. W waste. For details, see text.

It should be noted that Figs 2.12-2.16 do not include every possible type of configuration, as shown in subsequent chapters. Rather, they provide an overview of the wide variety of on-line coupled flow-through sensors and continuous unsegmented-flow analytical configurations. 

Figure 2.17 compares the different ways of regenerating flow-through sensors with the normal procedure for probe sensors the probe is successively immersed in the sample and buffer solution and removed from it prior to immersion into the next sample, which hinders automated functioning unless a robot station is lised (Fig. 2.17.A). On the other hand, on-line coupled flow-through sensors in continuous configurations lend themselves readily to convenient, automated regeneration.

Figure 2.18 shows the most relevant and/or usual types of transient signals provided by the flow-through (bio)chemical sensors used in the continuous configurations depicted in Figs 2.12-2.16 and the regeneration modes illustrated in Fig. 2.17. The two sequential steps (1 and 2) affecting the sensitive microzone of the flow-through sensor are distinguished.

Figure 5.13 — Irreversible-reusable flow-through sensor for the kinetic multidetermination of phosphate and silicate based on integrated sorption of a reaction product, reaction (/ situ reduction) and photometric detection. (A) Microsensor block (1) and components (2). (B) Continuous-flow configuration coupled on-line to the sensor. P peristaltic pumps SV switching valve W waste. For details, see text. (Reproduced from [39] with permission of the American Chemical Society).

Figure 2.11 — Functions and implicit advantages over conventional probe sensors of continuous configurations coupled on-line to a flow-through (bio)chemical sensor.

Figure 5.16 — Flow-through photometric sensor for the determination of traces of copper based on the immobilization of a chromogenic ligand (PAN) in a special flow-cell coupled on-line with a flow injection (A) or continuous-flow (B) configuration. IV injection valve SV switching valve W waste TGA thioglycollic acid. For details, see text. (Adapted from [42] with permission of Elsevier Science Publishers).

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