Chemistry Reference
In-Depth Information
enhancement in sensitivity or selectivity. Regarding electroanalytical approaches, alternative solvents can
provide wider potential windows that allow performing studies, synthesis or experiments unable to be
carried out in aqueous or conventional hydro-organic media. Furthermore, enhanced diffusion coefficients
of electroactive solutes can be achieved.
14.3.1 Ionicliquids
The use of ionic liquids (ILs) in electroanalysis is important from two fundamental sides. On the one hand,
they have been favourably explored as electrolytes and working media while, on the other hand, they have
been shown to be useful for the fabrication of electrode materials. From an electrochemical point of view, ILs
offer enormous advantages since they possess excellent conductivity, are thermally and chemically stable
and exhibit a wide accessible potential window. As an example of application, a recent description of a
solubilization and determination method of metal oxides pollutant particles in a single step, based on the use
of a specific IL, the protonated betaine bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], can be commented.
This IL solubilizes metal oxide particles due to the presence of acid functional groups in its structure. In this
way, the application of the conventional electrochemical method involving a strong acid treatment step to
dissolve the metal oxide particulates and an intricate detection process that makes in situ monitoring of metal
oxide particulate pollutants in soil, water and airborne particulates extremely challenging, can be avoided.
The detection step is carried out with an electrochemical sensor consisting of indium tin oxide (ITO)
printed electrodes (working, counter and pseudo reference electrode) and a thin layer of [Hbet] [Tf2N] coated
onto the ITO electrode as the selective solubilization medium and electrolyte (Figure 14.3). This figure
displays the voltammograms corresponding to the simultaneous detection of PbO, CdO and CuO present at
the 8 ng l
−1
level at room temperature. An insignificant stripping peak was observed after the addition of PbO,
CdO and CuO into pure [Hbet][Tf2N] upon a 2 min deposition time (black line). Conversely, larger, sharper,
and more defined separated peaks were obtained with the addition of 10 ng l
−1
bismuth oxide into [Hbet]
[Tf2N] and the same deposition time (grey line). The results clearly demonstrated that (1) the [Hbet][Tf2N]
can work as electrolyte as well as a solubilization medium to quickly dissolve the targeted metal oxides; (2)
the addition of bismuth greatly improved the stripping signals of PbO, CdO and CuO [71].
Another relevant application of ILs as working media is their use for polymer electro-synthesis. The
monomer is dissolved in IL medium and is electropolymerized at an appropriate electrode. In this way, the
use of organic solvents is avoided in many cases and, moreover, it can be achieved that the grown polymer
has especial characteristics. So, poly(pyrrol) (PPy) electrode coatings prepared in BMIMPF
6
exhibited better
electrocatalytic activity and higher selectivity for dopamine detection than those prepared in aqueous media
as a consequence of enhancing the oxidation current and decreasing the oxidation overpotential for this
compound [72]. The substitution of conventional media for ILs to perform the synthesis of electronic
conducting polymers can be also beneficial for the electro-mechanic properties of the polymer and its lifetime.
In these applications, the IL acts as electrolyte and as source and drain of dopants depending on the polymer
is in its oxidized or reduced form. Accordingly, the choice of the IL has a great influence on the polymer
redox chemistry, affecting the oxidation and reduction potential values as well as the number of voltammetric
signals. These differences were observed, for instance, in the synthesis of polythiophenes, where the cation
of the IL affects also the coating morphology [73].
Concerning the incorporation of ILs to the electrode materials, their use as agglutinants in the preparation
of carbon paste electrodes should be emphasized. The more relevant advantage of ILs with respect to the
other organic agglutinants conventionally employed is their conducting nature. The carbon ionic liquid
electrodes (CILEs) posses a high conductivity and are able to provide rapid electron transfer and low
overpotential values for diverse electroactive analytes. For example, Wang
et al
. developed a carbon paste
microelectrode by mixing of graphite and 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIM-PF
6
).
