Ivano Gebhardt Rolf Gutz
– Professor Titular –
Instituto de Química - Universidade de São Paulo
Av.Prof. Lineu Prestes, 748; 05508-900 São Paulo, SP, Brasil
www2.iq.usp.br/docente/?id=gutz, e-mail: firstname.lastname@example.org, Tel/Fax: (55) 11 3091 2150
P u b l i c a ç õ e s
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
Principais artigos publicados - 1996 a 2005
Relação completa e atualizada (mas sem resumos) encontra-se no Currículo Lattes - CNPq
A new electrolytic dissolution of aluminum alloys and determination of some constituents by inductively coupled plasma optical emission spectrometry
Tânia Grigoletto, Elisabeth de Oliveira and Ivano G.R. Gutz
Talanta, Volume 67, Issue 4, 15 October 2005, Pages 791-797
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 and Lúcio Angnes
Talanta, Volume 67, Issue 3, 15 September 2005, Pages 651-657
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
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.
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.
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.
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.
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.
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.
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
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).
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.
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.
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.
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.
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.
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.
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.
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
Química Nova, 2001, 24 (5), 689-692.
PALGROSSI, F.S.; PEDROTTI, J.J.; GUTZ, I.G.R.
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.
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.
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.
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.
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.
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. Electroana.l Chem., 1999, 468 (2), 150-157.
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
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
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.
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 and Maria L. Cruz
Methods in Enzymology, Volume 300, 1999, Pages 314-321
Selective determination of traces of copper by adsorptive accumulation of copper(I) benzotriazolate, transient amalgamation and anodic stripping voltammetry
Ana Maria Oliveira Brett , Sílvia H. P. Serrano , Mauro A. La-Scalea , Ivano G. R. Gutz and Maria L. Cruz
Electrochimica Acta, 1998, 43 (23), 3423-3429
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 and Ana Maria Oliveira Brett
Analytica Chimica Acta, 1998, 366 (1-3), 137-145.
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 22.214.171.124). 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
DE DONATO, A; PEDROTTI, J.J.; GUTZ, I.G.R.
Electroanalysis, 1997, 9(2), 110-114.
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 M 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.
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.
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.
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.
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.
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
PEDROTTI, J.; ANGNES, L.; GUTZ, I.G.R.
Electroanalysis, 1996, 8(7), 673-675.
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.