Teófilo R. F., Ceragioli H. J., Peterlevitz A. C., Baranauskas V., Ferreira M. M. C., Kubota L. T., "Optimization of voltammetric conditions for the determination of guaiacol and chloroguaiacol using boron-doped diamond electrode and RSM aproach". Águas de Lindóia, SP, Brazil, 10-15/09/2006: 10th International Conference on Chemometrics in Analytical Chemistry (CAC-2006, CAC-X), Book of Abstracts (2006) P008. Poster 008.
10th International Conference on Chemometrics in Analytical Chemistry P008
Optimization of voltammetric
conditions for the determination of
guaiacol and chloroguaiacol
using boron-doped diamond
electrode and RMS approach
Reinaldo F. Teófilo1*,
Helde J. Ceragioli2, Alfredo C. Peterlevitz2,
Vitor Baranauskas2,
Márcia M. C. Ferreira1,
Lauro T. Kubota1 teofilo@iqm.unicamp.br
1-Instituto de Química,
Universidade Estadual de Campinas
2-Faculdade de Engenharia
Elétrica, Universidade Estadual de Campinas
Keywords: guiacol, chloroguaiacol,
boron-doped diamond, RSM
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The determination of phenol and its derivatives in the environement is
one of the widespred analytical
procedures due to
their large use in industry and due to their
wide toxicity to humans and most aquatic
organisms. Phenols
can also impart unpleasant taste and odor to drinking water
and food products, even
at low concentrations.
According to published works, phenols toxicity
and organoleptic properties are
manifested in the ppb range.
Thus, there is a need for sensitive, reproducible, stable,
easy-to-use, and
low-cost analytical methods
for monitoring phenols and chlorinated phenols in water supplies1.
Among the
most sensitive analytical
methods to detect and quantify phenols,
the electroanalytical methods have
attracted very little attention
in the literature despite the fact these methods potentially
incur low costs and
employ fast analysis.
The reason for this limited use is probably due to the fact
that sensitive and stable
electrochemical detection
of these pollutants is usually
not possible with most electrode materials
because the
electrode passivation. Nevertheless, in recent
years, boron-doped diamond (BDD) has
demostrated to
be an attractive material for electroanalytical applications,
in view of tis unique properties
such as robustness,
chemical inertness, resistance to electrode fouling,
wide potential window and low
background current2.
Among the electroanalytical techniques generally used, square
wave voltammetry
(SWV) has proved
to be extremely sensitive for the detection
of phenolic compounds. However, the
utilization of SWV
and BDD belectrodes is not straightforward and a careful choice and
optimization of the
experimental parameters
is required to obtain a higher sensitivity.
The aim of this work was the optimization of
the voltammetric conditions using Response
Surface
Methodology (RSM)3
approach for determination of guiacol and chloroguaiacol simultaneously
using BDD
electrodes and SWV.
Guaiacol and chloroguaiacol have been determined
to be recalcitrant, toxic to
aquatic species,
genotoxic, lipophilic with
propensity for bioaccumulation.
BDD electrode was grown and
characterized by our research group.
SWV experiments were
performed using
an Autolab potentiostat (PGSTAT20). Pt wire
was used as counter electrode and a
saturated calomel electrode
(SCE) as reference. The potential was scanned in the
range from 0.5 up to
1.2 V. Central Composite
Design (CCD)3 was used in a
previous study. The parameters employed in this
stage were: frequency (Freq),
amplitude (Ampl) and pH. Their levels are shown in Table
1. Step potential
was 2 mV.
The concentration for both guiacol and chloroguaiacol
was fixed in 1.0x10-4
mol L-1. The
measurements were
performed in 5 ml of buffer McIlvaine 0.05
mol L-1. A cathodic
treatment in -3 V
during 3 s,
under vigorous agitation, afer at least 5
sequential analyses, was carried out to keep
the
precision of
measurements. The analyzed response
(r) was obtained in accordance with
equation:
r = (ip
. w-1 . v-1/2).106,
where ip is
the peak current in ampere (A), w
is the width at half peak height
and v
is scan rate (Vs-1).
pH and Ampl were significant for
both compounds and the values of its
result indicated a displacement
in the studied region. Thus a Doehlert design with two
variables (pH and
Ampl) was chosen
to investigate the new region. The studied levels for pH were
2.50, 2.87, 3.25, 3.62,
4.00 and for Ampl
were 0.07, 0.085, 0.1 V. The level for Freq was fixed in 35
Hz and the study was carried
out only with guaiacol,
since both compounds replied linearly for the experiments using CCD.
The model: r = 21.25 - 1.13 H + 0.84
Ampl
- 1.30 pH2 - 1.27 Ampl2
- 1.4 pHxAmpl obtained for
Doehlert design was significant
for regression and not significant for lack-of-fit
within a significance level,
a,
of 0.05. The analysis of surface response showed clearly that the
best levels for variables studied were:
pH 3.25, Ampl 0.08 V and
Freq
35 Hz.
Table 1. Parameters and
levels used in the CCD
These conditions provide a detection limit
____________________________________________
of 7.3x10-7 mol L-1
for chloroguiacol and
3.2x10-7 mol L-1
forguaiacol. The reached
-1.682 -1
0 1 1.682
ppb level was only
possible due to
____________________________________
multivariate data analysis.
Ampl. (V)
0.04 0.05
0.07 0.09 0.10
Freq. (Hz)
10 20
35 50
60
pH
4.73 5.00
5.40 5.80 6.07
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Acknowledgment: The authors thank CNPq for financial support.
References
1 Muna G. W.;
Quaiserova-Mocko V.; Swain G. M.; Anal. Chem.
2005, 77, 6542-6548.
2 Prado C.; Murcott
G. G.; Marken F.; Foord J. S.; Compton R. G. Electroanal. 2002,
14, 975-979.
3 Teófilo
R. F.; Ferreira M. M. C.; Quim. Nova 2006, 29, 338-350.