Lista
de publicações, com abstract
(Google Scholar)
Lista de
publicações, sem abstract (CV Lattes - CNPq)
Tese de livre -
docência - IQ-USP - 1985 (clique para consultar ou copiar)
Quimiometria
e Automação em Química Analítica: Algumas Contribuições
Tese de doutoramento - IQ-USP - 1978 (clique para consultar ou
copiar)
Estudos
de adsorção e de equilíbrios no sistema
cádmio(II)/piridina/cloreto.
Desenvolvimento de instrumentação
A r t i g o s p u b
l i c a d o s n o p e r í o d o
1 9 9 6 a 2 0 1 9
Photochemical and Photocatalytic Degradation of
1-Propanol Using UV/H2O2: Identification of Malonate as Byproduct
Fotocatálise mediada por TiO2 no estado nanoparticulado: revisão
da reatividade pelo conceito de traps e algumas aplicações em
química analítica
Photochemical Oxidation of Alcohols: Simple Derivatization
Strategy for their Analysis by Capillary Electrophoresis
Gold Leaf: From Gilding to the Fabrication of Disposable, Wearable
and Low-cost Electrodes
Chemical Analysis of Household Oxygen-Based Powdered Bleach: An
Engaging Approach to Teaching Sampling of Heterogeneous Materials
and Address Statistics
DNA adduct formation in the lungs and brain of rats exposed to low
concentrations of [13C2]-acetaldehyde
SANCHEZ, A.B.; GARCIA, C.C.M.; FREITAS, FP.;
BATISTA, G.L.; LOPES, F.S.; CARVALHO, V.H.; ROSEIN, G.E.; GUTZ,
I.G.R.; DI MASCIO, P.; MEDEIROS, M.H.G.
Chem.
Res. Tox., 2018, 31(5), 332-339
https://dx.doi.org/10.1021/acs.chemrestox.8b00016
Analysis of Methanol in the Presence of Ethanol Using a Hybrid
Capillary Electrophoresis Device with Electrochemical
Derivatization and Conductivity Detection
Online monitoring of electrocatalytic reactions of alcohols at
platinum and gold electrodes in acidic, neutral and alkaline media
by capillary electrophoresis with contactless conductivity
detection (EC-CE-C4D)
Determination of neutral diols and carboxylic acids formed during
glycerol electrooxidation process by capillary electrophoresis
with dual C4D
Fotoeletrocatálise em Semicondutores: Dos Princípios Básicos até
sua Conformação à Nanoescala
Oxygen Bleach under the Microscope: Microchemical Investigation
and Gas-Volumetric Analysis of a Powdered Household Product
Fast production of microfluidic devices by CO2 laser engraving of
wax-coated glass slides
Exhaled Breath Analysis in Heart Failures
Quick cold preparation of TiO2 nanolayers on gold from P25
suspensions–film structure, voltammetric behavior and
photocatalytic performance for the oxidation of EDTA under UVA-LED
irradiation
Impact of Exhaled Breath Acetone in the prognosis of patients with
heart failure. One year of Clinical Follow-up
MARCONDES-BRAGA, F.G.; BATISTA, G.L.; GUTZ,
I.G.R.; SALDIVA, P.H.N.; MANGINI, S.: ISSA, V.S.; AYUB-FERREIRA,
S.M.; BOCCHI, E.A.; COSTA PEREIRA, A.; BACAL, F.
PloS
one 11(12), e0168790 (December 28, 2016)
http://dx.doi.org/10.1371/journal.pone.0168790
Use of poly(methyl methacrylate)/polyethyleneimine flow
microreactors for enzyme immobilization
Unveiling the structure of polytetraruthenated nickel porphyrin by
Raman spectroelectrochemistry
Electrochemical Derivatization-Capillary
Electrophoresis-Contactless Conductivity Detection: A versatile
strategy for simultaneous determination of cationic, anionic and
neutral analytes
Novel photoelectrocatalytic approach aiming at the digestion of
water samples, estimation of organic matter content and stripping
analysis of metals in a special UV-LED irradiated cell with a
TiO2-modified gold electrode
Exhaled acetone as a new biomarker of heart failure severity
MARCONDES-BRAGA, F.; GUTZ, I.; BATISTA,
G.L.; SALDIVA, P.; AYUB-FERREIRA, S.; ISSA, V.; MANGINI, S.;
BOCCHI, E.; BACAL, F.
Chest, 2012, 142(2), 457-466.
http://dx.doi.org/0.1378/chest.11-2892
From Sample Processing to Quantification: A Full Electrochemical
Approach for
Neutral Analyte Derivatization, Capillary Electrophoresis
Separation and Contactless Conductivity Detection
Interview – main subjects: Personal Contributions and Views of the
Development of Analytical Chemistry in Brazil
Interview – main subject: Analytical Instrumentation in Brazil
Automated two-dimensional separation flow system with
electrochemically controlled preconcentration, stripping,
capillary electrophoresis and contactless conductivity detection
for trace metal ion analysis
Automation of an analysis system with microvolume porous membrane
sampling, capillary electrophoresis separation and contactless
conductivity detection for near-real-time monitoring of traces of
low-molecular-weight carboxylic acids in air
Capillary Electrophoresis Assisted Flow System
for In Situ Analysis of Products of Heterogeneous Electrocatalytic
and Catalytic Processes: Application to the Oxidation of Glycerol
Unraveling the Role of Sulfur Compounds in Acid Rain Formation:
Experiments on a Wetted Glass pH Electrode
Flow injection analysis of ethyl xanthate by gas diffusion and UV
detection as CS2 for process monitoring of sulfide ore flotation
Fully electrochemical hyphenated flow system for preconcentration,
cleanup, stripping, capillary electrophoresis with stacking and
contactless conductivity detection of trace heavy metals
Versatile microanalytical system with porous polypropylene
capillary membrane for calibration gas generation and trace
gaseous pollutants sampling applied to the analysis of
formaldehyde, formic acid, acetic acid and ammonia in outdoor air
A efervescente reação entre dois oxidantes de uso doméstico e a
sua análise química por medição de espuma
REZENDE, W.; DA SILVA, F.L.; RODRIGUES, A.S.;
GUTZ, I.G.R.
Bioluminescent sensor for naphthalene in air: cell immobilization
and evaluation with a dynamic standard atmosphere generator
Environmental formaldehyde analysis by active diffusive sampling
with a bundle of polypropylene porous capillary filaments followed
by capillary zone electrophoretic separation and contactless
conductivity detection
Flow Voltammetry
Microfluidic cell with a TiO2-modified gold electrode irradiated
by an UV-LED for in situ photocatalytic decomposition of organic
matter and its potentiality for voltammetric analysis of metal
ions
Flow injection analysis of ethyl xanthate by in-line dialysis and
UV spectrophotometric detection
Trace analysis of acids and bases by conductometric titration with
multiparametric non-linear regression
Wet deposition and related atmospheric chemistry in the São Paulo
Metropolis, Brazil: Part 3 – Trends in precipitation chemistry
during 1983 – 2003
Electronic micropipettor: A versatile fluid propulsion and
injection device for micro-flow analysis
In memoriam: Eduardo Neves, nosso eterno mestre
GUTZ, I.G.R.
Química Nova, 2006, 29 (5), 1150-1153.
http://dx.doi.org/10.1590/S0100-40422006000500041
A new electrolytic dissolution of aluminum alloys
and determination of some constituents by inductively coupled
plasma optical emission spectrometry
TÂNIA
GRIGOLETTO; ELISABETH DE OLIVEIRA; IVANO G.R. GUTZ
Talanta, Volume 67, Issue 4, 15 October 2005, Pages 791-797
https://doi.org/10.1016/j.talanta.2005.04.013
The new electrolytic dissolution in
batch of aluminum alloys samples as grains or turns and the
determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP
OES was investigated. In on-line electrodissolution procedures
described in the literature, samples were restricted to be in
the form of solid blocks or plates with one polished flat
face. Here, the sample was loaded in the barrel of a modified
disposable syringe (the anodic semi-cell) and pressed with a
modified plunger fitted with a platinum disk to establish
electrical contact with the analyte. This arrangement was
introduced in a beaker containing the electrolyte (1 mol L−1
HNO3) and a platinum wire as the cathode. The resulting
solution from electrodissolution (0.6 A) was used for the ICP
OES determinations. The influence of the aluminum
concentration increase on the determination of the elements
was evaluated. Electrodissolution of certified reference
materials and commercial samples revealed relative errors
lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti
(when their content is above 0.1%). Higher inaccuracies
(>10%) were observed for Mn and for Fe in B.C.S. 268/1
certified reference material. The proposed method presented a
relative standard deviations (R.S.D.) lower or circa 10% to
all of the elements (except Pb). In comparison with
traditional acid dissolution, the proposed electrodissolution
method is relatively fast (about 30 min), it is clean (there
is no projection of solution) and simple (heating and fumes
exhaust system were not necessaries).
FIA-potentiometry
in the sub-Nernstian response region for rapid and direct chloride
assays in milk and in coconut water
IRANALDO
SANTOS DA SILVA; EDUARDO MATHIAS RICHTER; CLAUDIMIR LÚCIO DO LAGO;
IVANO G.R. GUTZ; AURO ATSUSHI TANAKA; LÚCIO ANGNES
Talanta, Volume 67, Issue 3, 15 September 2005, Pages 651-657
https://doi.org/10.1016/j.talanta.2005.03.010
A simple and reliable
FIA-potentiometric system for rapid assays of chloride in
certain food samples is described and evaluated. The system is
constituted by an aquarium air pump to propel the carrier
solution, a manually operated injector, a homemade dialysis
flow cell, a solid-state chloride detector (Ag/AgCl), a
reference electrode and a multimeter connected to a
microcomputer for data acquisition. The dialysis unit enables
direct analysis of liquid food samples without any other
previous treatment. The principal novelties are the precision
(R.S.D. of 1.2% for whole milk) and rapidity (90
determinations/h) of FIA measurements near and below the lower
end of the linear (Nernstian) response region of the chloride
ion-selective electrode (ISE), with an estimated detection
limit (3 s) of 0.4 mg L−1 Cl− in the sample injected in donor
stream. Data of peak potential versus sample chloride
concentration (donor stream) was accurately fitted with a
quadratic polynomial over the range between 4 and 1000 mg L−1
(r2 = 0.9999) and used as a calibration curve. The method was
applied to the determination of chloride in milk and in
coconut water samples. The validation of the results was done
by comparison with a NIST reference material (milk) or by
capillary electrophoresis (coconut water). For all analysis,
no significant difference at a 95% confidence level was
observed.
Spectroelectrochemical determination of
chlorpromazine hydrochloride by flow-injection analysis
DANIEL, D.;
GUTZ, I.G.R.J
Pharm. Biomed. Analysis, 2005, 37 (2), 281-286
https://doi.org/10.1016/j.jpba.2004.10.048
An original, simple and sensitive flow-injection
spectroelectroanalytical method for the determination of
chlorpromazine in pure form or in pharmaceutical formulations
is described. The method is based on the formation of a stable
cationic radical by electro-oxidation in sulfuric acid medium
(0.1 mol l−1), monitored in situ at λ = 524 nm. The
determination of chlorpromazine hydrochloride in pure form or
in pharmaceutical formulations was explored, considering the
amperometric and the absorptiometric signal. The association
of these two signals enhanced the selectivity of the analysis
and proved decisive when other electroactive compounds or
excipients like ascorbic acid were present in the formulation.
The analytical parameters have been evaluated and the results
obtained using standard additions are in agreement with the
reference methods.
Simultaneous determination of three
surfactants and water in shampoo and liquid soap by ATR-FTIR
CAROLEI, L.;
GUTZ, I.G.R.
Talanta, Volume 66, Issue 1, 31 March 2005, Pages 118-124.
https://doi.org/10.1016/j.talanta.2004.10.005
It is demonstrated for the first time
that the principal constituents of a shampoo as well as of a
liquid soap –three surfactants and water– can be determined
directly, simultaneously and quickly in undiluted samples by
attenuated total reflection Fourier transform infrared
(ATR-FTIR) spectroscopy in the middle infrared region, despite
the broad absorption bands of the solvent. Two of the
surfactants, sodium lauryl ether sulfate (SLES) and
cocoamidopropyl betaine (CAPB), are common to both
formulations; alkylpolyglucoside (APG) is the third surfactant
of the liquid soap and cocodiethanolamide (CDEA), the
corresponding ingredient of the shampoo. Absorbance data of
the undiluted samples and of the calibration standards was
collected in the middle infrared region of the spectrum
(800–1600 and 1900–3000 cm−1). Two methods of multivariate
quantification were compared: classical least squares (CLS),
where absorbance data measured at 200 wavenumbers was
processed, and inverse least squares (ILS), where data at 10
selected wavenumbers was analyzed. A spectra normalization
procedure, based on a dominating water band, was examined.
Twenty-seven standard mixtures were used for each application,
consisting of all combinations at three concentration levels
of each surfactant, respectively the lower limit, the expected
value and the upper limit accepted in quality control. By
favoring wavenumbers where absorption bands of the minor
components (APG in the liquid soap and CDEA in the shampoo)
are more intense, good results were obtained for 18 simulated
samples of shampoo and 18 samples of liquid soap, no matter if
calculations were made by CLS or ILS. The relative errors for
water (major component, 84–88%) and SLES (7–10%) were always
below 2%; for CAPB (2–4%), APG (<2%) and CDEA (<2%),
they occasionally reached 5% of the component, an uncertainty
of less than 0.07% in terms of the sample weight.
Fast Mapping of Gunshot Residues by Batch
Injection Analysis with Anodic Stripping Voltammetry of Lead at
the Hanging Mercury Drop Electrode
DE DONATO,
A.; GUTZ, I.G.R.
Electroanalysis, 2005, 17 (2), 105-112.
https://doi.org/10.1002/elan.200303048
The forensic analysis of lead in
gunshot residues (GSR) sampled on the hands of potential
shooters is rendered faster, simpler and less expensive by a
new batch injection analysis (BIA) method, based on
differential pulse anodic stripping voltammetry (DPASV). A
simple "J" shaped adaptor was designed to direct the flux of
the analyte injected with a micropipettor onto the hanging
mercury drop electrode of any commercial electrode stand.
Sampling methods for GSR were compared and lifting with
adhesive tape was elected for field use. The tapes are glued
on polyethylene screens and stored in capped vials. Sampling
with multiple strips provides coarse mapping of the
distribution of lead on the shooter's hands. After a
dissolution/extraction step with chloroform/aqueous 0.10 mol
L-1 HCl, 100 L of the aqueous phase are injected during 25 s
for accumulation of lead on the HMDE at -0.60 V (vs. Ag/AgCl).
A detection limit of 20 ng/mL of Pb(II), outreaching for GSR
analysis, is reached without oxygen removal, at a frequency of
20 injections per hour. Results for sequences of shootings
with a revolver and a pistol are presented.
Extending the lifetime of the running
electrolyte in capillary electrophoresis by using additional
compartments for external electrolysis
JESUS, D.P.;
BRITO-NETO, J.G.A.; RICHTER, E.A.; ANGNES, L.; GUTZ, I.G.R.; LAGO,
C.L
Analytical Chemistry, 2005, 77 (2), 607-614.
https://doi.org/10.1021/ac0486645
The use of two additional reservoirs
to accommodate the electrodes of the power source is proposed
to improve the stability of the running electrolyte in
capillary electrophoresis. The basic idea is to use salt
bridges to connect those reservoirs to the ones containing the
capillary ends. Although simple, there are several issues that
can be considered in the design and implementation of such
system in order to prevent undesired transference of material
between the electrolysis and the main reservoirs. The use of a
sealed electrolysis reservoir without a gas phase, the use of
materials that ensure volume stability, and the use of bridges
as long as possible are three basic directions. A compromise
is involved in the dimensions of the sectional area of the
bridge, because a small area diminishes the amount of a
species transferred by diffusion but leads to an undesirable
increase of the electrical field during the electrophoretic
running. Thus, a bridge composed of a main wide-bore tube
connected to a small-bore capillary seems to give the best
performance for practical use. A simple electrolysis-separated
system was adapted to a preexisting capillary electrophoresis
system, and its performance was evaluated with a mixture of
tartaric, malic, and succinic acids that was separated in
sodium benzoate solution (pH 5.5) using the original equipment
and the modified one. Due to the water electrolysis and the
small buffering capacity of the electrolyte, there was a
significant pH change and consequently changes in the
effective mobilities of the analytes and loss of resolution
after a few runs using the original equipment. Using the
electrolysis-separated system, no significant change in the
migration time and resolution was observed even after 15 runs.
Besides the freedom to prepare running electrolytes with
electroactive species or unbuffered solution, high throughput
and the use of small reservoirs, such as the ones used in
microfluidic devices, are the main advantages of the system.
Disposable
twin gold electrodes for amperometric detection in capillary
electrophoresis
RICHTER,
E.M.; FRACASSI DA SILVA, J.A.; GUTZ, I.G.R.; LAGO, C.L.; ANGNES,
L.A.
Electrophoresis, 2004,25 (17), 2965-2969.
https://doi.org/10.1002/elps.200305960
An original, simple and sensitive flow-injection
spectroelectroanalytical method for the determination of
chlorpromazine in pure form or in pharmaceutical formulations
is described. The method is based on the formation of a stable
cationic radical by electro-oxidation in sulfuric acid medium
(0.1moll/l), monitored in situ at lambda=524nm. The
determination of chlorpromazine hydrochloride in pure form or
in pharmaceutical formulations was explored, considering the
amperometric and the absorptiometric signal. The association
of these two signals enhanced the selectivity of the analysis
and proved decisive when other electroactive compounds or
excipients like ascorbic acid were present in the formulation.
The analytical parameters have been evaluated and the results
obtained using standard additions are in agreement with the
reference methods.
Wet deposition and related atmospheric
chemistry in the São Paulo Metropolis, Brazil: Part 1 – Major
inorganic ions in rainwater as evaluated by capillary
electrophoresis with contactless conductivity detection
ROCHA, F.R.,
FRACASSI DA SILVA, J.A., LAGO, C.L., FORNARO, A.; GUTZ, I.G.R.
Atmos. Environ., 2003, 37 (1), 105-115.
https://doi.org/10.1016/S1352-2310(02)00722-7
The metropolitan region of São Paulo
(17.8 million inhabitants) presents serious air quality
problems. An official network monitors key air pollutants,
however, there is no regular program of evaluation of the wet
deposition and data about rainwater composition is scarce.
Opening a series of articles on this subject, capillary zone
electrophoresis with contactless conductivity detection
(CZE-CCD) is proposed and applied as a quick and inexpensive
alternative to ion chromatography for the determination of the
ionic composition of rainwater. Excellent resolution of the
peaks and sufficient sensitivity were obtained for major ions.
Switching from anion to cation determination is fast (30 min)
and as simple as inverting the polarity of the voltage supply
and changing the modifier added to the buffer solution.
CZE-CCD was applied to the study of wet-only deposition
collected in São Paulo during the period from May l997 to
March 1998. The volume weighted means of the anions, sulfate,
nitrate and chloride, were, respectively, 17, 22 and 29 μmol
l−1. Among the cations, ammonium was the dominating one, with
28 μmol l−1, followed by calcium, 23 μmol l−1, sodium, 12 μmol
l−1, and potassium, 5.8 μmol l−1. The wet flux of these anions
and cations were, respectively, 2.5, 2.2, 1.6, 0.78, 1.4, 0.43
and 0.35 g m−2 yr−1. By attributing all sodium to marine
origin, half of the chloride and more than 90% of all other
ions are ascribable to continental/anthropogenic sources.
Literature data for rainwater from inland regions (200 km
apart from São Paulo) reveals lower deposition of all ions but
H+. Absorption of NH3 and incorporation of calcium carbonate,
mainly in the metropolitan region itself, accounts for
decreased acidity. The enrichment in all other ions during the
studied period indicates the prevalence of the anthropogenic
emissions from the metropolis over continental sources and
explains the high correlation between the ions NO3−, SO42−,
and NH4+; the same ions responsible for a factor that, alone,
explains 42% of the variability in the PCA.
Wet deposition and related atmospheric
chemistry in the São Paulo Metropolis, Brazil: Part 2 –
Contribution of formic and acetic acids
FORNARO, A.;
GUTZ, I.G.R.
Atmos. Environ., 2003, 37 (1), 117-128.
https://doi.org/10.1016/S1352-2310(02)00885-3
Wet-only deposition samples were
collected at a site in the urban area of the São Paulo
metropolis between February (end of the rainy summer) and
October (beginning of spring) 2000, an atypical period due to
rainfall 40% below the 30-year average. The majority ions in
rainwater were measured by capillary zone electrophoresis with
contactless conductivity detection, CZE–CCD, applied for the
first time to the organic anions acetate and formate. The
volume weight mean (VWM) concentrations of the majority anions
NO3−, SO42− and Cl− were, respectively, 15.6, 9.5 and 4.7
μmoll−1. The VWM concentration of HCOO−t, (HCOO−+HCOOH) was
17.0 μmoll−1, about twice the 8.9 μmoll−1 of CH3COO−t. The VWM
concentration of free H+ was low (16.9 μmoll−1), corresponding
to pH 4.77. This denotes the relevance of species like
ammonia, analyzed as NH4+ (VWM=27.9 μmoll−1), and calcium
carbonate (VWM=5.3 μmoll−1 Ca2+) as partial neutralizers of
the acidity. By hypothetically assuming that H+ is the only
counterion of the non-sea-salt fraction of the dissociated
anions, their contribution to the total potential acidity
would decrease in the following order: sulfate (29%), formate
(29%), nitrate (26%), acetate (15%) and chloride (1%). The 44%
potential participation of the carboxylic acids reveals their
importance to the acidity of São Paulo's rainwater during the
study period. Direct vehicular emission of lower carboxylic
acids and aldehydes (in particular, acetic acid and
acetaldehyde) is singularly high in the metropolis due to the
extensive use of ethanol and gasohol (containing 20% of
ethanol) as fuels of the light fleet of 5.5 million cars; in
addition, regional atmospheric conditions favor the
photochemical formation of the acids, since concentrations of
ozone and aldehydes are high and solar irradiation is intense
at the 23°34′S latitude. The presence of higher concentrations
of HCOOH than CH3COOH indicates a prevalence of its
photochemical production by H2CO oxidation in the atmosphere.
A tribute to Professor Eduardo Neves for
outstanding contributions to the development of Electroanalytical
Chemistry in Brazil
GUTZ, I.G.R.
Symposium on Frontiers in Analytical Electrochemistry, 54th ISE e
Divisão de Eletroquímica e Eletroanalítica da SBQ, set/2003, São
Pedro, SP.
AllChemy, Série Alfa, 03-11-07 (artigo completo, 7 páginas).
http://allchemy.iq.usp.br/metabolizando/alfa031107.pdf
On the occasion of the 54th Annual
Meeting of the International Society of Electrochemistry,
September 2003, São Pedro, Brazil, in the Symposium on
Frontiers in Analytical Electrochemistry, a tribute is given
to Professor Eduardo F. A. Neves – on the year of the
celebration of his 70th birthday – for outstanding
contributions to the development of Electroanalytical
Chemistry in Brazil. In the next pages, an account is
presented of the scientific career and accomplishments of
Prof. Neves, highlighting his decisive actions to widespread
the knowledge and practice of Electroanalysis, as well as to
establish a prolific science school that, to a large extent,
merges Analytical Chemistry with Electrochemistry in its
research activities.
Ultra-simple adaptor to convert batch cells
with mercury drop electrodes in voltammetric detectors for flow
analysis
PEDROTTI,
J.; GUTZ, I.G.R.
Talanta, 2003, 60 (4), 695-705.
https://doi.org/10.1016/S0039-9140(03)00143-7
A simple, robust and fast-responding
flow adaptor for mercury drop electrodes (MDEs) is described.
An L-shaped PTFE tube with an internal diameter of 0.5 mm is
fixed with a silicone ring on the glass capillary of a MDE, in
such a way as to direct the outcoming flow onto the mercury
drop, from a distance of about 0.5 mm. Any commercial or
laboratory-made batch cell, provided with an MDE, serves for
the purpose. The level of supporting electrolyte in the cell
is maintained constant through a siphon or a lateral draining
orifice. The adaptor is compatible with all the different
brands and operating modes of the MDEs (free dropping,
controlled drop time, renewable static drop, hanging drop or
sessile drop). Flow injection experiments were conducted with
the following amperometric detection modes: sampled-DC,
reverse pulse amperometry (RPA), and anodic stripping
voltammetry (ASV). The FIA-RPA peaks presented a
R.S.D.<0.8% for 1.0×10−5 mol l−1 lead(II) (N=30,
Vsample=100 μl). The response time (0–63% of the signal
maximum) to a concentration step is 1.2 s for 500 μl
injections of 0.1 mmol l−1 ascorbic acid in acetate buffer at
a flow rate of 1 ml min−1, which corresponds to a response
volume of 20 μl. As an example of practical application,
copper(II) was determined in fertilizers by RPA using the
standard addition method, at an analytical frequency of 90
injections per h.
Quick production of gold electrode sets or
arrays and of microfluidic flow cells based on heat transfer of
laser printed toner masks onto compact discs
DANIEL, D.;
GUTZ, I.G.R.
Electrochemistry Communications, 2003, 5(9), 782-786.
https://doi.org/10.1016/j.elecom.2003.07.004
A process is described to speedily
produce in the laboratory, single or multiple coplanar gold
electrodes of any shape and with sizes ranging from 100 μm to
10 cm, as well as to assemble microfluidic flow cells with
them. The innovative combination of simple processes for ad
hoc design and production uses readily available equipment and
inexpensive materials, like recordable compact disks of the
gold sputtered type. The following steps are involved: drawing
of the electrode(s) on a microcomputer; laser printing of the
design on wax paper; heat-transfer of the toner onto the gold
surface of a peeled CD-R; etching of the gold layer from
unprinted regions; removal of the toner with a solvent;
activation; and use in conventional batch or flow cells. To
obtain microfluidic flow cells with 7–12 μm interlayer gap, a
gasket spacer of the desired shape is drawn and laser printed,
the toner layer is heat transferred onto one CD piece with
pre-etched electrodes and a second CD section is heat-sealed
on top of it. The functionality of these electrodes as well as
of the microfluidic flow cells is demonstrated by voltammetry
and flow injection amperometric analysis.
Flow injection spectroelectroanalytical
method for the determination of promethazine hydrochloride in
pharmaceutical preparations
DANIEL, D.;
GUTZ, I.G.R.
Anal. Chim. Acta, 2003, 494, 215-224.
https://doi.org/10.1016/S0003-2670(03)00903-6
The first flow injection
spectroelectroanalytical method for the determination of
promethazine hydrochloride has been developed. It is based on
the in situ detection of a colored cationic radical formed
during electroxidation at a gold electrode in sulfuric acid
medium (0.1 mol l−1) and it offers a number of advantages in
terms of simplicity, rapidity, selectivity and sensitivity
over many other approaches. The determination of promethazine
hydrochloride in pure form or in pharmaceutical formulations
was investigated, considering the amperometric and the
absortiometric signal. Although the amperometric signal alone
can be used for the determination of promethazine in simple
formulations like Fenergan (Rhodia-Farma), the photometric
signal might become decisive when other electroactive
compounds, such as dipyrone, are present in the formulation,
e.g. in Lisador (Farmasa). Promethazine was quantified in
Fenergan and Lisador. The results obtained using either
conventional calibration curves or standard additions, were
equivalent to those obtained with the official method
recommended in the British Pharmacopoeia (BP) and in agreement
with the labeled composition, for Fenergan. For Lisador, the
results for promethazine were within 2% of the nominal value
informed by the producer and the official method could not be
applied due to dipyrone interference.
O uso de radiação ultravioleta para o
pré-tratamento de amostra em análise inorgânica
CAVICCHIOLI,
A.; GUTZ, I.G.R.
Química Nova, 2003, 26, (6), 913-921.
http://www.scielo.br/pdf/%0D/qn/v26n6/a22v26n6.pdf
USE OF UV RADIATION FOR SAMPLE
PRETREATMENT IN INORGANIC ANALYSIS. The basic principles of UV
irradiation as sample pre-treatment step and its potential for
inorganic analysis are illustrated and discussed through
significant examples from the literature. Not only does this
overview cover the classical applications of this technique in
the decomposition of organic matter in electroanalysis, but it
also presents recent trends, including the increasing interest
in employing UV irradiation in flow analytical systems,
successful attempts to enhance its effectiveness and the
coupling with chromatographic and spectroscopic methodologies.
Furthermore, a number of relevant cases of UV-driven
derivatization reactions involving photo-sensitive inorganic
species are presented, showing some convenient options to
perform fast and reliable determination of inorganic and
organic analytes.
Effect of scavengers on the photocatalytic
digestion of organic matter in water samples assisted by TiO2
in suspension for the voltammetric analysis of heavy metals
CAVICCHIOLI,
A.; GUTZ, I.G.R.
J. Braz. Chem. Soc., 2002, 13 (4), 441-448. Free
acess
http://dx.doi.org/10.1590/S0103-50532002000400006
The influence of electron and hole
scavengers in the photocatalytic digestion of organic matter
in the presence of suspended particles of TiO 2
was investigated. The process, aiming at the electrochemical
determination of traces of heavy metals in water samples, was
followed through the recovery of the voltammetric wave of
Cd(II) in the presence of EDTA, chosen as model ligand that
mimics the complexing effect of natural dissolved organic
matter. The accelerating power of O 2 , acting
as electron scavenger, was confirmed. In the absence of O2, a
similar function is played by nitrate ions but not, as it
seems, by the analyte, Cd(II). On the other hand, CH 3
OH exhibits an antagonist effect as hole scavenger.
This observation may explain why the acetate (from the pH
buffer), used to control the medium acidity, leads to a
certain reduction in the photocatalytic yield.
Determination of low concentrations of the
flotation reagent ethyl xanthate by sampled DC polarography and
flow injection with amperometric detection
HIDALGO, P.;
GUTZ, I.G.R.
Talanta, 2001, 54, 403-409.
https://doi.org/10.1016/S0039-9140(01)00311-3
A polarographic DCtast method with the
static mercury drop electrode, SMDE, was developed for
determination of the flotation collector ethyl xanthate (EtX)
in the concentration range from 1×10−5 to 8×10−5 M. The
potentiality of the method was demonstrated by evaluating the
capacity of powdered galena ore (PbS) to adsorb EtX in a
titration-like procedure. Sulfide could be determined
simultaneously with EtX because in NaOH electrolyte their
anodic waves are well separated (E1/2congruent with−0.72 and
−0.42 V versus Ag/AgCl, respectively). In addition, a new FIA
method was developed by adapting a simple device to the tip of
the glass capillary of a mercury electrode and doing
amperometric detection at a fixed potential of −0.1 V, always
in the DCtast mode. No oxygen removal was required.
Reproducible results were obtained at a frequency of 72
injections per h, with automatic renewal of the SMDE every
second. The calibration curve for freshly prepared EtX
standards rendered a straight line from 5×10−6 to 8×10−5 M
with correlation coefficient of 0.997, suitable for real
applications in flotation processes and its effluents.
Long-optical-path thin-layer
spectroelectrochemical flow cell with inexpensive gold electrodes
DANIEL, D.;
GUTZ, I.G.R.
Electroanalysis 2001, 13 (8-9), 681-685.
https://doi.org/10.1002/1521-4109(200105)13:8/9<681::AID-ELAN681>3.0.CO;2-F
A novel long-optical-path thin-layer
spectroelectrochemical cell for flow systems is described and
its suitability for in situ UV-visible applications,
demonstrated. Gold electrodes with flat surface are simply cut
from standard recordable CDs of the gold sputtered type. After
removal of the protecting polymer layer, the area of the
working and auxiliary coplanar electrodes is delineated by
scraping off the gold layer. A set of twin electrodes is
placed face to face within any standard spectrophotometric
cuvette with 1.0 cm optical path. The sample is introduced
with a syringe or peristaltic pump and reaches the bottom of
the working electrodes through a PTFE tube. Evaluation was
done with o-tolidine in acidic medium as a model system, and
gave good results under stationary conditions and in the FIA
mode. The appropriateness of the cell for flow operation
including FIA, good potential control, simplicity of
construction and maintenance, easy adaptability to existing
instrumentation and a cost lower than any other proposed model
are advantages of the innovative cell design.
Injetor multicanal com válvulas de
estrangulamento para análise em fluxo
PALGROSSI,
F.S.; PEDROTTI, J.J.; GUTZ, I.G.R.
Química Nova, 2001, 24 (5), 689-692.
http://dx.doi.org/10.1590/S0100-40422001000500017
PINCH VALVE INJECTOR FOR FLOW
ANALYSIS. An important component for the automation of flow
injection analysis (FIA) systems is the sample injection
valve. A simple and inexpensive commutator with 16 pinch
valves (8 normally open and 8 closed) was developed and
configured as a multichannel injection valve. It is activated
by a single solenoid of 3 Kgf, powered by a pulsed driver
circuit, controlled by a microcomputer or a switch. FIA with
spectrophometric detection of potassium dichromate solution
was used for the evaluation of the new injection valve and its
comparison with other valves, for sample loops of 50, 100,
200, 300 and 500 mL. The repeatability was favorable (RSD 1.0%
for 15 injections at each loop volume) compared to a manual
injector, an electropneumatic injector and an injector
configured with three mini solenoid valves (RSD 1.1, 1.3 and
1.0%, respectively, for15 injections at each loop volume).
Propulsor pneumático versátil e isento de
pulsação para sistemas de análise em fluxo
MATOS, R.C.;
FONTENELE, R.S.; GUTZ, I.G.R.; ANGNES, L.; PEDROTTI, J.J.
Química Nova, 2001, 24 (6), 795-798.
http://dx.doi.org/10.1590/S0100-40422001000600017
A VERSATILE AND PULSATION FREE
PNEUMATIC IMPELLER FOR FLOW ANALYSIS SYSTEMS. Aquarium air
pumps are proposed and evaluated as pneumatic liquid
propulsion devices for flow injection and continuos flow
analysis (FIA and CFA) systems. This kind of pump is widely
available at a very low cost and it can sustain a pressure
around of 4 psi (0.28 bar) indefinitely. By applying this air
pressure onto a solution contained in a reservoir flask, it is
possible to reach flow rates of up to 12.5 mL min-1 for
circuits comprising reactors, made from 0.8 i.d. tubing with a
length of 100 cm. The precise adjustment of flow rate below
the maximum one can be made with a simplified needle valve or
inserting in series a short length of capillary tube. The
absence of flow pulsation is a definite advantage in
comparison with peristaltic pumps, especially when
amperometric detection is elected, as confirmed experimentally
in FIA and CF applications.
In-line TiO 2-assisted
photodigestion of organic matter in aqueous solution for
voltammetric flow analysis of heavy metals in water samples
CAVICCHIOLI,
A.; GUTZ, I.G.R.
Anal. Chim. Acta, 2001, 445, 127-138.
http://dx.doi.org/10.1590/S0100-40422001000600017
A novel enhanced photocatalytic
digestion method for water samples, based on the addition, to
the sample, of a suspension of TiO2 (anatase) and aiming at
voltammetric heavy metal determination, is presented and
evaluated. The quelate Cd(II)–EDTA acted as a model system in
this investigation. The voltammetric wave of Cd(II) is
effectively suppressed in the presence of EDTA in excess, but
it experiences recovery as the coordinating capacity of the
ligand is destroyed. It was observed that the presence of a
TiO2 suspension 0.1% w/w neither affects the polarographic
wave of the metal ion nor hinders its stripping voltammetry,
although some catalyst adheres to the mercury drop. The
retention of TiO2 on the electrode is further minimised by
operating in the flow injection mode with renewable Hg drop
electrodes. The voltammetry of samples of 1 mmol l−1 EDTA
solutions, buffered with AcH/Ac− to pH 4 and containing 0.1
mmol l−1 Cd(II), collected during irradiation, revealed
significant acceleration of the recovery of the Cd(II) signal
in the presence of TiO2. It was demonstrated that the method
is perfectly fit for flow analysis through a system that
integrates the following stages: injection of sample,
monosegmented with air bubbles; addition of TiO2 to the
sample; in-line photodigestion; debubbling; degassing
(dissolved O2 removal); accumulation of Cd(Hg) at the mercury
electrode; and voltammetric stripping. Complete recovery of
the 0.01 mmol l−1 Cd(II) signal was obtained for 150 μl sample
plugs containing 0.1 mmol l−1 EDTA, after a transit time of
155 s in the irradiation chamber, at 30°C. Degradation of EDTA
in real matrixes was also carried out.
Determination of traces of uranium in
environmental samples using a flow injection system with
amperometric catalytic detection
AGUIAR,
M.A.S; MARQUEZ, K.S.G.; GUTZ, I.G.R.
Electroanalysis, 2000, 12 (10), 742-746.
https://doi.org/10.1002/1521-4109(200006)12:10<742::AID-ELAN742>3.0.CO;2-Z
A new method for flow injection
analysis (FIA) of traces of uranium by catalytic amperometric
detection in nitrate medium is described. Interfering oxygen
was removed by in-line degassing. A simple adapter was
designed to afford FIA with batch cells comprising a hanging
mercury drop electrode. The carrier electrolyte consisted of
10 mM LiNO33+10 mM LiNO3. The method is simple, rapid (up to
60 injections/h) and precise (RSD=1.0 % for n=10 and CU=80
nM), presenting a LD of 13 pg of U or 3 nM (3 SD). Dissolution
of solid samples (rock and soil) was abbreviated by employing
a mixture of nitric and hydrofluoric acids in microwave heated
closed vessels, followed by liquid-liquid extraction with TBP.
Analysis of reference materials and intercomparison with other
techniques gave very favorable results.
A Batch Injection Analysis System for
Ascorbic Acid Determination Using Amperometric Detection on a
Sessile Mercury Drop Electrode
DE DONATO,
A; PEDROTTI, J.J.; GUTZ, I.G.R.
Electroanalysis, 1999, 11 (15), 1124-1129.
https://doi.org/10.1002/(SICI)1521-4109(199911)11:15<1124::AID-ELAN1124>3.0.CO;2-I
A batch injection analysis (BIA)
system, which uses an automatic mercury electrode (AME) as an
amperometric detector, is described. The capillary of this AME
was adapted in an inverted position through the bottom of a
simple cylindrical electrochemical cell, in order to generate
more stable sessile drops and to grant free access for the tip
of the programmable micropipettor. The BIA system was
evaluated by using the electrochemical oxidation of L-ascorbic
acid to dehydroascorbic acid on the sessile mercury drop
electrode. Acetate buffer solution (50 mM, pH 4.8) was used as
supporting electrolyte. The working electrode was operated at
+0.230 V (vs. Ag/AgCl). The effect of the dispensing rate, of
the dispensed volume, of the distance between the mercury drop
and the pipettor tip, as well as of the solution level in the
cell were evaluated. Injections of 50 µL were suitable to
reach a detection limit of about 2.5 µM (450 ppb). At the 50
µM ascorbic acid level, an RSD of 1.6 % (N=35) was observed
with or without mercury drop renewal between injections. A
frequency of 300 injections per hour may be reached when the
drop is renewed sporadically. The new BIA method was applied
to the determination of ascorbic acid in packed/canned
tropical fruit juices. Selectivity was granted by differential
measurements of the peak current before and after exposure of
samples to ascorbate oxidase (from cucumber).
Overcoming oxygen quenching in fluorescence
spectrometry with a highly efficient in-line degassing device
interfaced with a flow cell
PEDROTTI,
J.; LIMA, S.; COICHEV, N; GUTZ, I.G.R.
Anal. Chim. Acta, 2000, 422, 131-137.
https://doi.org/10.1016/S0003-2670(00)01060-6
To overcome the quenching effect of
oxygen in fluorescence spectrometry, an in-line flow degassing
device (FDD) was successfully applied to the removal of oxygen
from sample solutions. The FDD consisted of a 3 m long coil of
capillary silicone rubber tubing, installed in a glass flask
maintained under reduced pressure of N2 (2.400 Pa). To avoid
recontamination of the emerging flow with O2, the connection
of the silicone tube with the fluorimetric cell is made with
flexible silica capillary tube. Solutions can be injected with
a syringe or feed with a pump. Aqueous solution of
ruthenium(II) tris-bipyridil chloride, subject to quenching by
oxygen, served as a luminescent probe. The performance was
checked against independent amperometric measurements of O2
with a Clark cell, that correlated well with the O2 obtained
from the fluorescence data using the Stern–Volmer
relationship. At a flow rate of 1.0 ml min−1, the
concentration of O2 (measured amperometrically) dropped from
8.24 mg l−1 to 15 μg l−1 for a residence time of 34 s in the
FDD, rendering the oxygen quenching effect on [Ru(bipy)3]2+
undetectable. The FDD compares favorably with direct inert gas
purging of the solution in efficiency and speed. Moreover, it
is compatible with flow injection analysis. A frequency of 35
determinations per hour was attained at 1 ml min−1, with good
repeatability of the peaks (R.S.D.=0.8%, n=25 injections of
200 μl of 1×10−4 M [Ru(bipy)3]2+).
Determination of the surface charge density
of a mercury electrode by extrusion: a new method for correction
of the Faradaic component
BRITO,
M.S.L.; ANGNES, L.; BRETT, C.M.A; GUTZ, I.G.R.
J. Electroanal. Chem., 1999, 468 (2), 150-157.
https://doi.org/10.1016/S0022-0728(99)00161-8
The accurate determination of the
surface charge density at the mercury / solution interface by
the method of extrusion of mercury drops is impaired by the
faradaic current caused by traces of electroactive species.
This paper describes a new design of a hanging mercury drop
electrode with accurate control of the extruded electrode
area, to within 0.1%, together with a new and reliable
procedure for correction of the faradaic current. The
procedure is based on first obtaining the correction
parameters in the presence of increasing amounts of
electroactive species and then using these parameters for
correction of the faradaic component so as to obtain the
surface charge density of the electrode. Implementation of the
method with a microcomputer controlled system provides
automatic acquisition of corrected electrode charge density
values as a function of the electrode potential. The results
obtained with this new method are in excellent agreement with
those obtained by other methods, as illustrated for aqueous
sodium fluoride solution.
Critical Comparison of Four Simple Adaptors
for Flow Amperometric and Stripping Voltammetry with Mercury Drop
Electrodes in Batch Cells
CAVICCHIOLI,
A; DANIEL, D.; GUTZ, I.G.R.
Electroanalysis, 1999, 16 (5), 391 - 398
https://doi.org/10.1002/elan.200302864
Electrochemical batch cells with mercury drop electrodes,
MDEs, are readily available from a number of producers and
widely used in electroanalysis for polarography, voltammetry
and stripping voltammetry. To increase sample throughput and
reduce reagent and sample consumption, the tendency is to
couple the MDE with flow analysis systems (e.g., FIA, SIA or
BIA). Many special flow cells for MDEs are described in the
literature, but it is easier to convert existing commercial
batch cells to flow operation. To assess the performance of
such flow adaptors, four models were chosen because they are
directly fitted to the glass capillary of any MDE, light
enough not to impair the mechanical drop knocker and can be
effortlessly built in the laboratory. They were all found
adequate for flow amperometry and stripping voltammetry, with
differences in sensitivity, flow rate dependence, response
time, drop stability, tolerance to bubbles, uncompensated
resistance and recontamination of disposed analyte from the
electrolytic bath. Two of them, a simple L-shaped PTFE tube
and an upstream nozzle holder made from a disposable pipette
tip, gather a larger set of desirable features.
Analysis and Speciation of Traces of Arsenic
in Environmental, Food and Industrial Samples by Voltammetry: a
Review
CAVICCHIOLI,
A; LA SCALEA, M.A.; GUTZ, I.G.R.
Electroanalysis, 1999, 16 (9), 697 - 711
https://doi.org/10.1002/elan.200302936
Voltammetric approaches for the
determination of arsenic and speciation at trace levels are
critically appraised in a review covering the literature from
1970 to 2002. Special attention is devoted to stripping modes
and to issues related to the choice of working material and
supporting electrolyte. A section is dedicated to the
management of real samples and aspects of sample preparation.
An extensive compilation, organized by real sample type,
gathers essential experimental conditions. Potentiometric
stripping analysis is introduced for sake of comparison. The
coupling of voltammetric detection or preaccumulation with
FIA, chromatography, capillary electrophoresis and ICP
techniques is also addressed.
Eletrodos modificados com DNA: uma nova
alternativa em eletroanálise
LA-SCALEA,
MAURO A., SERRANO, SILVIA H.P. AND GUTZ, IVANO G.R.
Química Nova, 1999, 22 (3), 417-424.
DNA-MODIFIED ELECTRODES: A NEW
ALTERNATIVE FOR ELECTROANALYSIS. The first
studies about DNA electrochemistry appeared at the end of the
fifties. The voltammetric techniques
became important tool for the DNA conformational analysis,
producing evidences about
DNA double helix polimorphism. The new techniques based on
electrodes modification with nucleic
acid enlarged the use of the electrochemical methods on the
DNA research. DNA electrochemical
biosensors are able to detect specific sequences of DNA bases,
becoming important alternative for
the diagnosis of disease, as well as in the carcinogenic
species determination. Besides, the use of
DNA biosensors in the mechanism study of biological drug
actions can be useful for drug design.
Voltammetric Behaviour of Metronidazole at
Mercury Electrodes
LA-SCALEA,
MAURO A., SERRANO, SILVIA H.P. AND GUTZ, IVANO G.R.
J. Braz. Chem. Soc., 1999, 10 (2), 127-135.
http://www.scielo.br/pdf/%0D/qn/v22n3/1096.pdf
Metronidazole is the most important
drug of the group of 5-nitroimidazoles and possesses toxicity
to anaerobic micro-organisms DNA being the main target for
their biological action. The mechanism of biological action of
metronidazole is dependent upon the nitro group reduction
process. The reduction of metronidazole is pH dependent in
acid medium and four electrons are involved in the complete
reduction to the hydroxylamine derivative. In aprotic medium
the reduction of the metronidazole occurs in two steps, the
first involving one electron to form the nitro radical and the
second step involving three more electrons until the formation
of the hydroxylamine derivative. In this paper the mechanism
of reduction of metronidazole was studied by using the
voltammetric techniques: d.c. polarography, differential pulse
polarography and cyclic voltammetry using the mercury drop as
the working electrode.
Mechanism of interaction of in situ produced
nitroimidazole reduction derivatives with DNA using
electrochemical DNA biosensor
ANA MARIA
OLIVEIRA BRETT , SÍLVIA H. P. SERRANO , MAURO A. LA-SCALEA , IVANO
G. R. GUTZ, MARIA L. CRUZ
in - Methods of Enzymology, Volume 300, 1999, Pages 314-321
https://doi.org/10.1016/S0076-6879(99)00137-8
The electrochemical reduction of nitroimidazoles follows a
complex mechanism and in theory the nitro group is able to
receive up to six electrons to form the corresponding amine.
Under anaerobic and low oxygen pressure conditions
metronidazole follows a reduction mechanism similar to that of
nitrobenzene. Electrochemical reduction of nitroimidazole
derivatives shows two reduction waves in aqueous acid media,
the first involving four electrons and corresponding to the
reduction of the nitro group to form the intermediate
hydroxylamine (-NHOH) and the second involving two electrons
and corresponding to the reduction of the hydroxylamine to
amine (-NH2). Using three different electrode materials (bare
glassy carbon electrode, mercury thin film electrode, and DNA
biosensor), it has been verified that hydroxylamine formation
involves four electrons and is pH dependent. This chapter
shows that the DNA biosensor developed provides a new
perspective to the research and study of the mechanism of
action of nitroimidazoles with DNA.
Selective
determination of traces of copper by adsorptive accumulation of
copper(I) benzotriazolate, transient amalgamation and anodic
stripping voltammetry
VALBERES B.
DO NASCIMENTO, IVANO G. R. GUTZ
Electrochimica Acta, 1998, 43 (23), 3423-3429.
https://doi.org/10.1016/S0013-4686(98)00088-7
Anodic stripping voltammetry with
adsorptive accumulation of amalgam forming metals is proposed
and demonstrated for the determination of traces of copper
ions in the presence of benzotriazole, HBTA (an excellent
corrosion inhibitor for copper). The accumulation of the metal
ions is accomplished, as customary, by adsorption on the
mercury electrode of a coordination compound with a suitable
ligand. Specifically, copper(II) is reduced to copper(I) and
accumulated as the Cu(I)BTA complex on a hanging mercury drop
electrode at 0.0 V vs SCE, under convection. Subsequently,
copper(I) is reduced to the amalgam by applying a potential
step to −0.4 V during 15 s or less. Finally, the potential is
scanned in the positive direction and the differential pulse
anodic peak of the re-oxidation of Cu(Hg) to Cu(I)BTA is
recorded. A 2 min accumulation period provides a detection
limit of 3 × 10−9 M and an analytical curve linear up to 8 ×
10−7 M. Accumulation for 10 min (or more) lowers the detection
limit to 8 × 10−10 M (or lower). The new mode opens
alternatives to improve the selectivity of cathodic stripping
methods involving amalgam forming metals, and to reconsider
ligands that give rise to unsatisfactory cathodic stripping
peaks, such as HBTA.
Flow-injection determination of catechol with
a new tyrosinase/DNA biosensor
PATRÍCIA
DANTONI, SÍLVIA H. P. SERRANO, IVANO G. R. GUTZ, ANA MARIA
OLIVEIRA BRETT
Analytica Chimica Acta, 1998, 366 (1-3), 137-145.
https://doi.org/10.1016/S0003-2670(98)00102-0
Biosensors find application in flow
analysis due to their high selectivity and sensitivity.
Decrease in the response during extended use, originated by
degradation, inhibition or structural changes of the enzyme or
leaching of active components by the flow, is the prevailing
problem. As an alternative to additives and preparation
techniques cited in the literature, it is proposed to use DNA
as a matrix for improving preservation of the activity of a
diphenol-sensor-based tyrosinase, Tyr, (EC 1.14.18.1). The
Tyr–DNA mixture was incorporated into carbon paste,
CP–DNA–Tyr, or applied on glassy carbon, GC–DNA–Tyr. The
CP–DNA–Tyr, covered by a membrane -of Cuprophan, presented
superior performance in amperometric operation under flow
conditions (electroreduction of the products of the enzymatic
oxidation of diphenols in the presence of O2). In comparison
with paste electrodes without DNA, CP–Tyr, a current increase
of one order of magnitude was observed for catechol FIA peaks,
with good repeatability during several hours of operation. The
response decayed ca. 50% after every 3 to 4 days of use (with
dry storage at 4°C overnight). Original performance was
recovered by simply substituting the used paste for a new
portion of stock paste, stable for 2 months under
refrigeration. Evaluation of 18 different substrates and
potential interferents indicated that, at the adopted
potential of −0,15 V vs. Ag/AgCl, only p-cresol gives a
response comparable to catechol. Flow-injection determination
of catechol samples was conducted at a frequency of 30
injections/h, with linear response from the detection limit of
1×10−6 up to 5×10−5 mol l−1.
Comparison of the voltammetric behavior of
metronidazole at a DNA-modified glassy carbon electrode, a mercury
thin film electrode and a glassy carbon electrode
BRETT, A.M.O.;
SERRANO, S.H.P.; GUTZ, I.G.R.; LA-SCALEA, M.A.
Electroanalysis, 1997, 9 (2), 110-114.
https://doi.org/10.1002/elan.1140090204.
The electroanalytical performance at
three electrodes: DNA‐modified galssy carbon electrode, mercury
thin film electrode and glassy carbon electrode, for the study
of the electrochemical reduction of metronidazole is compared.
All three electrodes showed a similar trend in the reduction
mechanism for metronidazole, depenent on pH in the acid and
neutral region and independent in alkaline media, although there
was a shift in the peak potentials to more negative values when
a bare glassy carbon electrode was used compared to the other
two. Besides the advantage of using a solid electrode for the
reduction of metronidazole, the DNA‐modified galssy carbon
electrode enables a lower detection limit of 1.0 μM owing to the
preconecentration of the drug on the electrode surface, which is
not the case for the mercury thin film or bare glassy carbon
electrodes.
A low cost and high performance conductivimeter
ROCHA, R. T.,
GUTZ, I.G.R., LAGO, C. L.
J. Chem.
Educ., 1997, 74(5), 572-574.
https://doi.org/10.1021/ed074p572
A two-electrode conductivimeter is described, which keep
good performance in spite of its low cost. It is composed of a
triangular wave generator, a current-to-voltage converter, and a
precision half-wave rectifier. All these functions were
implemented with only one integrated circuit TL084. A 3
1/2-digits multimeter is used as the display. Four scales allow
measurements over a wide range of conductance (0.01 µS to 19.99
mS). To ensure the low cost and robustness, a stainless steel
electrode was developed. The low amplitude and high frequency of
the oscillator allow good measurements with this kind of
electrode, giving, in some cases, even better results than
commercial ones. Anyway, platinum electrode is the better choice
for very oxidant media. Electronic diagrams and complete list of
components as well as examples of applications are shown.
Electrochemical
Reduction of metronidazole at a DNA-modified glassy carbon
electrode
BRETT, A.M.O.;
SERRANO, S.H.P.; GUTZ, I.G.R.; LA-SCALEA, M.A.
Bioelectrochem. Bioenerg., 1997, 42(2), 175-178.
https://doi.org/10.1016/S0302-4598(96)05122-7
The electrochemical reduction of
metronidazole was investigated using, for the first time, the
newly developed DNA-modified glassy carbon electrode. The
results are compared with reduction at bare glassy carbon
electrodes. The potentials for reduction were less negative when
using the DNA-modified glassy carbon electode although the
mechanism was the same. A potential-pH dependence of one
electron per proton was observed in acid media whereas for
neutral and alkaline solution no dependence was found. The
DNA-modified glassy carbon electrode enables preconcentration of
the sample for chosen times on the electrode surface which is
convenient for analytical applications. The limit of detection
using the DNA-modified glassy carbon electrode at pH 4.5 with 2
min preconcentration is 1.67 μM, and without preconcentration it
is three times higher, 3.25 μM. At a bare glassy carbon
electrode, where preconcentration is not possible, the limit of
detection for the same pH is 3.44 μM.
A
flow-through cell based on an array of gold microelectrodes
obtained from modified integrated circuit chips
AUGELLI, M.A.;
NASCIMENTO, V.B.; PEDROTTI, J.J; GUTZ, I.G.R; ANGNES, L.A.
The Analyst, 1997, 122, 843-847.
https://doi.org/10.1039/A701519D
The construction of a flow-through cell
incorporating an array of gold microelectrodes is described and
its application to flow injection analysis with amperometric
detection is presented. Simple modification of almost any
conventional integrated circuit chip, used as an inexpensive
source of pre-assembled gold micro-wires, leads to the rapid and
successful preparation of arrays of 8–48 elements. The polymeric
encapsulation material from the top face of the chip is removed
by abrasion until the gold micro-wires (used to interconnect the
silicon circuit to the external contact pins of the chip) are
disrupted and their transversal (elliptical) sections become
exposed. Once polished, the flat and smooth top surface of the
gold microelectrode-array chip (MEAC) is provided with a spacer
and fitted under pressure against an acrylic block with the
reference and auxiliary electrodes, to form the electrochemical
(thin-layer) flow cell, while the contact pins are plugged into
a standard IC socket. This design ensures autonomous electric
contact with each electrode and allows fast dismantling for
polishing or substitution. The performance of flow cells with
MEACs was investigated utilizing the technique of reverse pulse
amperometry without oxygen removal. A method was established for
the determination of the copper concentration in sugar cane
spirit, regulated by law for beverages. Samples from industrial
producers and small-scale (alembic) brewers were compared. With
a 24 MEAC, a detection limit of 30 µg l-1 of copper (4.7 × 10-7
mol l-1 of CuII for 100 µl injections) was calculated. Routine
operation was established at a frequency of 60–90 determinations
per hour. Intercomparison with atomic absorption spectrometric
determinations resulted in excellent agreement.
Arrays
of gold microelectrodes made from split integrated circuit chips
NASCIMENTO,
V.B.; AUGELLI, M.A.; PEDROTTI, J.J; GUTZ, I.G.R; ANGNES, L.A.
Electroanalysis, 1997, 9(4), 335-339.
https://doi.org/10.1002/elan.1140090415
A simple and inexpensive way to
fabricate arrays of gold microelectrodes is proposed. Integrated
circuit chips are sawed through their middle, normal to the
longest axis, leading to destruction of the silicon circuit and
rupture of the gold wires that interconnect it with the external
terminals. Polishing the resulting rough surface converts the
tips of the wires embedded in the chip halves into arrays of
gold microdisks of about 25 m diameter. The number of active
microelectrodes (MEs), of an array depends on the number of pins
in the chip, n, being typically (n/2)-4. These MEs can be used
individually or externally interconnected in any combination.
X-ray images of the chips and micrographs of the resulting
surface of the polished arrays have revealed variable distances
between neighbor MEs, which are however, larger than 10 times
the radius of the disks. This feature of the MEs prevents
diffusional cross-talk between electrodes. The use of these
microdisk electrodes for analytical purposes exhibits sigmoidal
voltammograms, and chronoamperometric experiments confirm the
nonlinear i vs. t1/2 plots, typical for processes where radial
diffusion prevails, Satisfactory uniformity was observed for the
response of each electrode of an array, indicating similarity of
geometry and disk areas. The potentialities of these MEs were
demonstrated by the determination of cadmium at ppb levels using
square wave voltammetry with preconcentration. Due to the
relative ease with which these MEs can be manufactured and their
good performance in (chemical) analysis, wide applications in
electrochemistry and electroanalysis is envisioned.
Voltammetric
behavior of nitroimidazoles at a DNA-biosensor
BRETT, A.M.O.;
SERRANO, S.H.P.; GUTZ, I.G.R.; LA-SCALEA, M.A.; CRUZ, M.L.
Electroanalysis, 1997, 9 (14), 1132-1137.
https://doi.org/10.1002/elan.1140091419
The newly developed DNA-biosensor is a
very promising tool for the investigation and study of the
action of drugs specifically designed to interact with DNA. In
this work the electrochemical reduction of nitroimidazole drugs
was studied in the presence of DNA immobilized onto the surface
of a glassy carbon electrode. This enabled preconcentration of
the drug onto the electrode surface, which was then
electrochemically reduced to the corresponding hydroxylamine
which followed by reoxidation give the nitroso compound and
subsequently an azoxycompound. Moreover, as the target of the
nitroimidazole action was the DNA, the damage caused to DNA on
the electrode surface by areduction product of this drug could
be detected in situ.
Miniaturized reference electrodes with
microporous polymer junctions
The construction and evaluation of a
simple and effective mini-reference electrode is presented. Major
innovations are the use of high density microporous polyethylene
for the restricted flow junction between the internal and external
electrolyte and a polypropylene disposable pipette tip as the
electrode body. Low electrolyte bleeding, reduced size, relatively
low electrical resistance and simplified procedure of construction
are some of the advantages of the presented design. These
characteristics make this electrode particularly suitable for use
with small-volume cells and flow cells, as well as applications
where chloride contamination should be avoided. Other applications
for the microporous membrane in electroanalysis are introduced.