Question

Why is the chemical balance important for a chemical sensor? Explain how the
Chemical equilibrium is used for the detection (qualitative and quantitative) of species
chemicals Indicate 2 different types of equilibria that are exploited for the design of sensors
molecular

Answer 1

A chemical sensor is a self-contained device that is capable of providing real-time analytical information about a test sample. By chemical information we understand here the concentration of one or more chemical species in the sample. The response from the sensors is not consistent between sensors nor stable over time. So a calibration which establishes an unequivocal relationship between the measured quantity and concentration of analyte is needed to be done which maintains the chemical balance whch is important for producing accurate and reproducable results.

A chemical sensor involves two processes namely recognition and transduction.

Recognition processes follow the equation in which A is the analyte, R is the recognition receptor and P is a product of the analyte–receptor interaction:

The double arrow indicates that the recognition process is a reversible process at equilibrium. Reversibility of the recognition process arises from the fact that the product P involves noncovalent chemical bonds, such as ionic bonds, hydrogen bonds and van der Waals interactions. The recognition process can be characterized by its equilibrium constant which is defined as:

  

where symbols c represent concentrations of the species indicated by subscripts. This equilibrium constant indicates the affinity of the recognition receptor for the analyte. Great affinity results in a high value of the equilibrium constant. If the sensor response depends on the product concentration, the response will be determined by the concentration of the analyte in the sample.

The two different equilibria exploited during sensor design depends on the two most important aspect of sensing i.e. recognition and selectivity. There is an equlibria established between the sensing element and analyte(A) to be qualitatively detected or quantitatively concentration measured but along with that there is a competing equilibria established between the sensing element and another species(B) acting as interferrant. The lower the value of the second equilibrium constant, the better will be the selectivity of the sensor.

     ;

   ;

Selectivity good when