Redox ions that are less active or inactive at conventional electrode-electrolyte
surfaces can be detected at liquid-liquid interfaces by applying electrochemical
analysis the interface of two immiscible electrolytes [104]. This technique holds an
extra advantage of pre-saturation with water molecules, thereby less affected by
humidity. MWCNT based ionic liquid (1-butylimidazole bromide immobilized on
an epoxy group of poly(glycidyl methacrylate)-MWCNT composite) electrodes
were used for voltammetric detection of phenolic compounds [121]. Ionic liquid
can profoundly be applied as Ion Selective Electrodes (ISEs) as an alternative to
plasticizers and ion exchangers. Hydrophobic RTIL [N8, 8, 8, 1] [C 4 C 4 N] containing dicyclohexano-18-crown-6 (DCH18C6) as ionophore was used for the
potentiometric detection of K
+ in water [122]. Thin microporous membrane containing valinomycin and hydrophobic [N12, 12, 12, 1] [TFPB] ionic liquid was
applied for amperometric detection of K
+ and Na
+ [123]. Low-melting ionic solids
(LMISs) viz. [N6, 6, 6, 6] [BSB], [N8, 8, 8, 8] [BSB] and [N8, 8, 8, 1] [BSB] were
applied for the potentiometric determination of salicylate, perchlorate, thiocyanate
and iodide ions in water [124].
5 Limitations and Plausible Solutions
Fouling of the electrode surface appears as a serious matter of concern when it
comes to detection of biological or organic pollutants. This creates a strong impact
when it comes to on time monitoring of wastes in the stability as well as performance time. A large number of electrode surface cleaning techniques are available
but it is preferred to have low cost electrochemical sensors. Poisoning of electrode
surface is an important issue that must be solved while working with electrochemical sensors, which is time consuming and steps must be taken for continuous
monitoring of the samples.
ISEs are simple-to-use and cost-effective devices which are highly effective for
environmental analysis. However many practical challenges that are faced during
their application in analysis (water samples from rivers or lakes) includes electrodes
carryover, drift, their dissolution with the time, surface passivation and fouling
[125]. The problem of surface fouling can be overcome by regular cleaning of
electrode surface with analyte solution at a very low concentration. The preconditioning of electrode in analyte may lead to fast response, increased stability and
reduce the problem of electrode drift and dissolution. Passivation and fouling can
be combatted by using ISEs in Flow Injection Analysis and surface should be
frequently calibrated.
Application of ionic liquids will prove an effective method for reducing toxicity
due to mercury electrode. Some of the minor drawbacks related to electrochemical
sensors includes their lower shelf life of six to one year depending upon samples
they are being used with, limited temperature range which requires keeping the
temperature of samples highly stable, low humidity and high temperatures dries out
the surface of electrolyte.
Materials in Electrochemical Detection of Water Pollutants
177
surfaces can be detected at liquid-liquid interfaces by applying electrochemical
analysis the interface of two immiscible electrolytes [104]. This technique holds an
extra advantage of pre-saturation with water molecules, thereby less affected by
humidity. MWCNT based ionic liquid (1-butylimidazole bromide immobilized on
an epoxy group of poly(glycidyl methacrylate)-MWCNT composite) electrodes
were used for voltammetric detection of phenolic compounds [121]. Ionic liquid
can profoundly be applied as Ion Selective Electrodes (ISEs) as an alternative to
plasticizers and ion exchangers. Hydrophobic RTIL [N8, 8, 8, 1] [C 4 C 4 N] containing dicyclohexano-18-crown-6 (DCH18C6) as ionophore was used for the
potentiometric detection of K
+ in water [122]. Thin microporous membrane containing valinomycin and hydrophobic [N12, 12, 12, 1] [TFPB] ionic liquid was
applied for amperometric detection of K
+ and Na
+ [123]. Low-melting ionic solids
(LMISs) viz. [N6, 6, 6, 6] [BSB], [N8, 8, 8, 8] [BSB] and [N8, 8, 8, 1] [BSB] were
applied for the potentiometric determination of salicylate, perchlorate, thiocyanate
and iodide ions in water [124].
5 Limitations and Plausible Solutions
Fouling of the electrode surface appears as a serious matter of concern when it
comes to detection of biological or organic pollutants. This creates a strong impact
when it comes to on time monitoring of wastes in the stability as well as performance time. A large number of electrode surface cleaning techniques are available
but it is preferred to have low cost electrochemical sensors. Poisoning of electrode
surface is an important issue that must be solved while working with electrochemical sensors, which is time consuming and steps must be taken for continuous
monitoring of the samples.
ISEs are simple-to-use and cost-effective devices which are highly effective for
environmental analysis. However many practical challenges that are faced during
their application in analysis (water samples from rivers or lakes) includes electrodes
carryover, drift, their dissolution with the time, surface passivation and fouling
[125]. The problem of surface fouling can be overcome by regular cleaning of
electrode surface with analyte solution at a very low concentration. The preconditioning of electrode in analyte may lead to fast response, increased stability and
reduce the problem of electrode drift and dissolution. Passivation and fouling can
be combatted by using ISEs in Flow Injection Analysis and surface should be
frequently calibrated.
Application of ionic liquids will prove an effective method for reducing toxicity
due to mercury electrode. Some of the minor drawbacks related to electrochemical
sensors includes their lower shelf life of six to one year depending upon samples
they are being used with, limited temperature range which requires keeping the
temperature of samples highly stable, low humidity and high temperatures dries out
the surface of electrolyte.
Materials in Electrochemical Detection of Water Pollutants
177