Chemistry Reference
In-Depth Information
film electrode constructed by a photolithographic microfabrication process was prepared. This fabrication
procedure provides small size, cost effective, reproducible, mass produced and disposable devices, and have
been applied to the determination of trace nickel by adsorptive stripping voltammetry [48].
14.2.1.4
Other electrode materials
Boron-doped diamond film electrodes (BDDFE) can be also considered as another environmentally friendly
alternative for electroanalytical chemistry. BDDFE has attracted the attention of researchers because it
exhibits a stable background current, wide potential window for aqueous and non-aqueous electrolytes, high
thermal conductivity, high hardness, high electrochemical stability, low organic molecule adsorption and
high sensitivity for analytical purposes [49]. There are numerous examples of applications of BDDFE in the
literature especially for the determination of pharmaceutical compounds such as nitrofurantoin [49],
lyncomicin [50] or fluvastatin [51], as well as in food analysis for the determination of antioxidant mixtures
[52], among others.
Other environmentally friendly materials have also been used as electrode modifiers for the development
of stripping methods for metal traces and organic compounds. This is the case of
-CD), a
versatile oligosaccharide acting as a host molecule for a wide variety of possible guests. Different
CD-derivatives have been employed for this purpose. For example, a highly sensitive and reproducible lead
sensor based on a cyclodextrin-modified gold electrode was described. A self-assembled monolayer
(SAM) of thiolated
β
-cyclodextrin (
β
-cyclodextrin (MEA-ß-CD) ) was
prepared on the gold electrode to construct a mercury-free sensor for Pb
2+
with a linear response over
the 1.7
β
-cyclodextrin (6-(2-mercapto-ethylamino)-6-deoxy-
β
10
−9
M [54]. Similar
configurations were also used for the determination of organic compounds. An example is the development
of a sensor to detect azobenzene, a toxic industrial pollutant, by means of a gold electrode modified with a
6-O-toluenesulfonyl-
×
10
−8
- 9.3
×
10
−7
M concentration range and a detection limit of 7.1
×
-CD-6-OTs) layer. The inclusion complex formed at the modified electrode
allowed azobenzene determination in solution by square wave voltammetry with a detection limit of 1.0
β
-CD (
β
×
10
−10
M. An additional advantage is the reusability of the
β
-CD-modified electrode. When azobenzene on the
β
-CD
layer is irradiated by UV light (360 nm) in stirred solution, it is detached from the
-CD layer [54].
The determination of uranyl in environmental samples is a challenging task that has given rise to numerous
procedures. Against methods using expensive instrumentation such neutron activation analysis or inductively
coupled plasma emission spectrometry, electrochemical methods based on stripping analysis are faster, easier
and cheaper. Although the majority of these methods have been performed using mercury electrodes, other
electrode materials can be also used. For instance, a carbon paste electrode containing benzo-15-crown-5
(B15C5) has been reported recently for trace determination of uranyl ion using differential pulse voltammetry.
Due to the good compatibility between the ionic radius of uranyl and the cavity size of the crown ether,
modification of carbon paste using B15C5 resulted in facile electrochemical reduction of UO
2
2+
with enhanced
current. The proposed method demonstrated a good sensitivity, with a limit of detection of 0.03
β
g l
−1
.
Furthermore, it was also selective and, so, it was successfully applied to the determination of uranyl in the
presence of Pb
2+
and Cd
2+
as well to the determination of UO
2
2+
in ores and industrial effluents [55].
Metal electrodes such as copper electrodes are also employed for some especial applications. So, a clean
alternative method for the determination of chemical oxygen demand (COD) using a copper electrode as an
electrocatalytic sensor was described. The measuring principle is based on the oxidation current of organic
compounds in the wastewater. An analytical linear range of 53.0-2 801.4 mg l
−1
COD with a detection limit
of 20.3 mg l
−1
COD was achieved. The procedure was successfully applied to the COD determination in
wastewater from soft industries. The results were in good agreement with those obtained using the conven-
tional (i.e. dichromate) COD method. Accordingly, the COD value of a sample could be determined in a
simple, rapid and accurate manner and the end products did not contain toxic metals [56].
μ
