2.2 Conductometric
Charge concentration is measured in terms of solution resistance in such electrochemical sensors. They lack species-selectivity and are much effective in cases
where total ion concentration is below a certain permissible maximum level or can
be used as detector in ion exchange chromatography after the separation of ions as
online detectors. It measure the change in electrical conductivity on the surface of
electrode. They are simple, cost effective and miniaturized sensors but are least
selective in all the variants of electrochemical techniques. There are various kinds
of resistance such as electrical, contact resistance (between electrodes and selective
layer), bulk and surface resistance. This may affect the sensing activity of the
selective layer of electrode and analyte and thereby creates hurdles in differentiating
the ions or molecules being analyzed.
Various types of Conductometric sensors have been developed in past few years.
Some of them employ ionophores based polymeric membranes for the detection of
potassium, calcium, ammonium and Lithium ions with the sensitivity in micro
molar concentration range and fast response time. Their stability is very high and
can be used for several weeks [28]. Enzyme immobilized Conductometric sensors
can be employed for toxic organic compounds such as organophosphorus pesticides
and heavy metals from micro to nano molar concentration range [29]. Similarly
many other biosensor based Conductometric techniques have been developed that
has been discussed further in this chapter. Application of molecularly imprinted
polymers (MIPs) is also broadly discussed in terms of application in case of organic
pollutants and metal ions.
2.3 Voltammetric
Current is measured as a function of applied potential in these type of sensors. They
provide much insight of species present and work with very low detection limits (up
to Pico molar) using state-of-the-art instrumentation and analyte pre-concentration
on the surface of electrodes. Separation of species are not required in these sensors
and it can be combined with Amperometric or coulometric sensors once the
voltammetric profile has been assigned to the mixture of analyst [4]. Keys steps for
voltammetric determination of pollutants includes preconcentration and stripping of
ion of the interest. These steps leads to higher selectivity and sensitivity. The ions of
interest are collected in a working electrode and then they are oxidized or reduced
to send back them in solution. These voltammetric sensor have been proved to be
highly efficient and can be used for solution with very low detection range (nano to
Pico molar concentration). This gives an extra advantage of monitoring of trace
metals in water bodies. They are also proved worthy in multi-elemental analyses,
speciation of trace elements and in situ detection. There are mainly two major
166
A. Ojha
Charge concentration is measured in terms of solution resistance in such electrochemical sensors. They lack species-selectivity and are much effective in cases
where total ion concentration is below a certain permissible maximum level or can
be used as detector in ion exchange chromatography after the separation of ions as
online detectors. It measure the change in electrical conductivity on the surface of
electrode. They are simple, cost effective and miniaturized sensors but are least
selective in all the variants of electrochemical techniques. There are various kinds
of resistance such as electrical, contact resistance (between electrodes and selective
layer), bulk and surface resistance. This may affect the sensing activity of the
selective layer of electrode and analyte and thereby creates hurdles in differentiating
the ions or molecules being analyzed.
Various types of Conductometric sensors have been developed in past few years.
Some of them employ ionophores based polymeric membranes for the detection of
potassium, calcium, ammonium and Lithium ions with the sensitivity in micro
molar concentration range and fast response time. Their stability is very high and
can be used for several weeks [28]. Enzyme immobilized Conductometric sensors
can be employed for toxic organic compounds such as organophosphorus pesticides
and heavy metals from micro to nano molar concentration range [29]. Similarly
many other biosensor based Conductometric techniques have been developed that
has been discussed further in this chapter. Application of molecularly imprinted
polymers (MIPs) is also broadly discussed in terms of application in case of organic
pollutants and metal ions.
2.3 Voltammetric
Current is measured as a function of applied potential in these type of sensors. They
provide much insight of species present and work with very low detection limits (up
to Pico molar) using state-of-the-art instrumentation and analyte pre-concentration
on the surface of electrodes. Separation of species are not required in these sensors
and it can be combined with Amperometric or coulometric sensors once the
voltammetric profile has been assigned to the mixture of analyst [4]. Keys steps for
voltammetric determination of pollutants includes preconcentration and stripping of
ion of the interest. These steps leads to higher selectivity and sensitivity. The ions of
interest are collected in a working electrode and then they are oxidized or reduced
to send back them in solution. These voltammetric sensor have been proved to be
highly efficient and can be used for solution with very low detection range (nano to
Pico molar concentration). This gives an extra advantage of monitoring of trace
metals in water bodies. They are also proved worthy in multi-elemental analyses,
speciation of trace elements and in situ detection. There are mainly two major
166
A. Ojha