Flow-through sensors cells

Qin, W., Zhang, Z., and Liu, H., Chemiluminescence flow-through sensor for copper based on anodic stripping voltammetric flow cell and ion-exchange column with immobilized reagents., Anal. Chem., 70, 3579, 1998. 

One other, very descriptive classification of flow-through sensors is based on the location of the active microzone and its relationship to the detector. Thus, the microzone can be connected (Figs 2.6. A and 2.6.B) or integrated (Fig. 2.6.C) with the measuring instrument. Sensors of the former type use optical or electric connections and are in fact probe sensors incorporated into flow-cells of continuous analytical systems they can be of two types depending on whether the active microzone is located at the probe end (e.g. see [17]) or is built into the flow-cell (e.g. see [18]) — in this latter case. 

The most frequently used electrochemical flow-through sensors are depicted schematically in Fig. 2.9. A the electrode is brought into contact with the sensitive microzone, which is accommodated in the flow-cell... 

Thermal and mass flow-through sensors rely on differential measurements owing to the low selectivity of these types of detection. They use two flow-cells arranged in series (Fig. 2.9.B) or parallel (Fig. 2.9.C), each containing a sensitive microelement (a piezoelectric crystal or a thermistor). One of the cells houses the sensitive microzone, whereas the other is empty or accommodates an inert support containing no immobilized reagent (e.g. see [35]). 

Flow-through sensors integrating detection and a chemical or biochemical reaction rely on immobilization in the probe proper or the flow-cell (or a special housing included in it) of a species intended to take part in or catalyse the reaction by which the analyte, viz. the catalyst or reagent, is measured, according to which the sensors described in this Chapter are divided into two broad categories. 

Figure 3.34 — Manifolds for implementation of a sensor containing a packed non-regenerable reagent and a regenerable fluorophore. (A) Flow-through sensor system 1 eluent vessel 2 pump 3 injection valve 4 TCPO reactor 5 CL cell 6 light-tight box with PMT 7 amplifier 8 recorder. (B) Design of the packed two-layer sensor 1 inlet capillary 2 inlet cap with frit 3 quartz tube 4 TCPO layer 5 frit 6 luminophore layer 7 outlet cap with frit 8 outlet capillary. (C) Manifold for implementation of the previous cell in biochemical applications (Reproduced from [240] and [241] with permission of the American Chemical Society and Elsevier Science Publishers, respectively).

Most flow-through sensors integrating retention and detection involve placement of an inert support in the flow-cell of a non-destructive spectroscopic detector where the analytes or their retention products are retained temporarily for sensing, and then eluted. Rendering these sensors reusable entails including a regeneration step suited to the way retention is performed. 

A photometric flow-through sensor for the determination of carbamate pesticides (carbofuran, propoxur and carbaryl) based on similar principles as regards the detector and sensor used (a diode array spectrophotometer and a flow-cell packed with C,g resin, respectively) was employed to monitor the formation of the products resulting from hydrolysis of the analytes and online coupling of the respective phenols with diazotized sulphanilic acid. This... 

Commercial instruments for both contacting and noncontacting electrode types come in the form of meters, probes, sensors and flow-through cells. Top-of-the-line instruments will have temperature compensation (a thermistor) built in. It is a simple instrument with the following components a conductivity cell, electrodes and a voltage supply. The conductivity cell consists of two platinum plates with an AC voltage applied between them. The eluent flows through the cell and the current, which depends on the concentration and type of ions, is measured. A conductivity detector responds to all ions but not to molecular compounds like ethanol and water. 

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