Sensors based on two sample donor -acceptor streams

2 Sensors based on two sample (donor)-acceptor streams 

This type of sensor is schematically depicted in Fig. 5.4.B. The sensing microzone is crossed by two streams rather than one. One such stream acts as the donor and contains the aspirated or injected sample, which is conditioned in order to provide a gaseous reaction product. The other stream acts as the acceptor for the volatile species transferred across the gas-diffusion membrane that isolates the two streams. 

These sensors differ fi-om ordinary gas-diffusion units in the fact that the analytical reaction (derivatization of volatile species) and detection take place simultaneously immediately after the continuous separation step. They also differ from (usually electrochemical) sensors using a static internal solution. In this respect, they resemble the sensor reported by DeGrandpe [12], from which they differ in that the sample is not passed through the sensor, even though the reagent is. 

Continuous circulation of the acceptor solution, where the sensing process takes place, makes them reusable and hence of practical interest. The acceptor solution may contain the ingredients needed to regenerate the reagent when this is immobilized on the sensing microzone. 

There are two possible configurations for this type of flow-through sensor integrating gas diffusion, reaction and detection that differ in whether the reagent is dissolved in the acceptor solution or immobilized on a sensing microzone located near the diffusion membrane. The descriptions below are based on such a difference. 

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