Integrated detection-separation

Figure 2.1 — Variants of integrated reaction, separation and detection in continuous-flow analytical systems. (1) Reaction/separation. (2) Reaction/detec-tion. (3) Separation/detection. (4) Reaction/separation/detection.

The equipment required to develop this type of sensor is very simple and resembles closely that used to implement ordinary liquid-solid separations in FI manifolds. The only difference lies in the replacement of the packed reactor located in the transport-reaction zone with a packed (usually photometric or fluorimetric) flow-cell accommodated in the detector. Whether the packing material is inert or active, it should meet the following requirements (a) its particle diameter should be large enough (< 80-100 fim) to avoid overpressure (b) it should be made of a material compatible with the nature of the integrated detection system e.g. almost transparent for absorbance measurements) and, (c) the retention/elution process should be fast enough to avoid kinetic problems. 

Flow-through sensors based on integrated reaction, separation and detection... 

Figure 5.1 — Classification of (bio)chemical flow-through sensors based on integrated reaction, separation and detection according to whether the three processes take place sequentially (A,B) or simultaneously (C) at the sensing microzone. S sample R reagent. (Reproduced from [1] with permission of the Royal Society of Chemistry).

Figure 5.2 — Classification of (bio)chemical flow-through sensors based on integrated reaction, separation and detection according to the type of separation technique involved.

Figure 5.3 shows the different possible ways in which the ingredients of the (bio)chemical reaction can take part in the sensing process. For example, the analyte can be retained temporarily and take part in the separation process. The reagent can be present in the solution used to immerse the sensor or immobilized in a permanent fashion on a suitable support. Also, the catalyst can be introduced directly across a membrane or be permanently immobilized. Finally, the reaction product can be the species transferred in the separation process or also be temporarily immobilized. These and other, more specific alternatives that are described below are all possible in (bio)chemical flow-through sensors integrating reaction, separation and detection. 

The use of capillary separations, an NMR probe that contains multiple coils, and the associated capillary fluidics to deliver the samples to and from the coils is the next step in probe development. A future exciting development will be the interfacing of such intelligent NMR probe and fluidic systems with other integrated detection modalities such as fluorescence, absorbance and mass spectrometry to provide an integrated system capable of delivering unprecedented structural information from complex samples. 

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