Ivano G. R. Gutz

Surface enhanced Raman spectra of benzotriazole adsorbed on a copper electrode

Abstract The surface-enhanced Raman spectra of benzotriazole adsorbed on a silver electrode have been investigated in order to study the formation of complexes at the electrode surface as a function of the applied potential, the pH and the type of halide in the electrolyte solution. The use of a pseudo-halide, SCN−, in the electrolyte (KNO3) solution allowed the simultaneous adsorption of SCN− and benzotriazole to be followed.

Wet deposition and related atmospheric chemistry in the São Paulo metropolis, Brazil: Part 2 contribution of formic and acetic acids

Abstract Wet-only deposition samples were collected at a site in the urban area of the Sao 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 NO 3 − , SO 4 2− and Cl − were, respectively, 15.6, 9.5 and 4.7 μmol l −1 . The VWM concentration of HCOO − t , (HCOO − +HCOOH) was 17.0 μmol l −1 , about twice the 8.9 μmol l −1 of CH 3 COO − t . The VWM concentration of free H + was low ( 16.9 μmol l −1 ), corresponding to pH 4.77. This denotes the relevance of species like ammonia, analyzed as NH 4 + ( VWM =27.9 μmol l −1 ), and calcium carbonate ( VWM =5.3 μmol l −1 Ca 2+ ) 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 Sao Paulos 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 CH 3 COOH indicates a prevalence of its photochemical production by H 2 CO oxidation in the atmosphere.

Electrochemical reduction of metronidazole at a DNA-modified glassy carbon electrode☆

Abstract 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.

Flow-injection determination of catechol with a new tyrosinase/DNA biosensor

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 48C 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 ofˇ0,15 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 110 ˇ6 up to 510 ˇ5 mol l ˇ1 . # 1998 Elsevier Science B.V.

Voltammetric Behaviour of Metronidazole at Mercury Electrodes

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.

Microfluidic cells with interdigitated array gold electrodes: Fabrication and electrochemical characterization.

Microfluidic flow cells combined with an interdigitated array (IDA) electrode and/or individually driven interdigitated electrodes were fabricated and characterized for application as detectors for flow injection analysis. The gold electrodes were produced by a process involving heat transfer of a toner mask onto the gold surface of a CD-R and etching of the toner-free gold region by short exposure to iodine-iodide solution. The arrays of electrodes with individual area of 0.01cm(2) (0.10cm of lengthx0.10cm of width and separated by gaps of 0.05 or 0.03cm) were assembled in microfluidic flow cells with 13 or 19mum channel depth. The electrochemical characterization of the cells was made by voltammetry under stationary conditions and the influence of experimental parameters related to geometry of the channels and electrodes were studied by using K(4)Fe(CN)(6) as model system. The obtained results for peaks currents (I(p)) are in excellent agreement with the expected ones for a reversible redox system under stationary thin-layer conditions. Two different configurations of the working electrodes, E(i), auxiliary electrode, A, and reference electrode, R, on the chip were examined: E(i)/R/A and R/E(i)/A, with the first presenting certain uncompensated resistance. This is because the potentiostat actively compensates the iR drop occurring in the electrolyte thin layer between A and R, but not from R to each E(i). This is confirmed by the smaller difference between the cathodic and anodic peak potentials for the second configuration. Evaluation of the microfluidic flow cells combined with (individually driven) interdigitated array electrodes as biamperometric or amperometric detectors for FIA reveals stable and reproducible operation, with peak heights presenting relative standard deviations of less than 2.2%. For electrochemically reversible species, FIA peaks with enhanced current signal were obtained due to redox cycling under flow operation. The versatility of microfluidic flow cells, produced by simple and low-cost technique, associated with the rich information content of electrochemical techniques with arrays of electrodes, opens many future research and application opportunities.

Exhaled Acetone as a New Biomarker of Heart Failure Severity

BACKGROUND Heart failure (HF) is associated with poor prognosis, and the identification of biomarkers of its severity could help in its treatment. In a pilot study, we observed high levels of acetone in the exhaled breath of patients with HF. The present study was designed to evaluate exhaled acetone as a biomarker of HF diagnosis and HF severity. METHODS Of 235 patients with systolic dysfunction evaluated between May 2009 and September 2010, 89 patients (HF group) fulfilled inclusion criteria and were compared with sex- and age-matched healthy subjects (control group, n = 20). Patients with HF were grouped according to clinical stability (acute decompensated HF [ADHF], n = 59; chronic HF, n = 30) and submitted to exhaled breath collection. Identification of chemical species was done by gas chromatography-mass spectrometry and quantification by spectrophotometry. Patients with diabetes were excluded. RESULTS The concentration of exhaled breath acetone (EBA) was higher in the HF group (median, 3.7 μg/L; interquartile range [IQR], 1.69-10.45 μg/L) than in the control group (median, 0.39 μg/L; IQR, 0.30-0.79 μg/L; P < .001) and higher in the ADHF group (median, 7.8 μg/L; IQR, 3.6-15.2 μg/L) than in the chronic HF group (median, 1.22 μg/L; IQR, 0.68-2.19 μg/L; P < .001). The accuracy and sensitivity of this method in the diagnosis of HF and ADHF were about 85%, a value similar to that obtained with B-type natriuretic peptide (BNP). EBA levels differed significantly as a function of severity of HF (New York Heart Association classification, P < .001). There was a positive correlation between EBA and BNP (r = 0.772, P < .001). CONCLUSIONS EBA not only is a promising noninvasive diagnostic method of HF with an accuracy equivalent to BNP but also a new biomarker of HF severity.

Environmental formaldehyde analysis by active diffusive sampling with a bundle of polypropylene porous capillaries followed by capillary zone electrophoretic separation and contactless conductivity detection

Compared to other volatile carbonylic compounds present in outdoor air, formaldehyde (CH(2)O) is the most toxic, deserving more attention in terms of indoor and outdoor air quality legislation and control. The analytical determination of CH(2)O in air still presents challenges due to the low-level concentration (in the sub-ppb range) and its variation with sampling site and time. Of the many available analytical methods for carbonylic compounds, the most widespread one is the time consuming collection in cartridges impregnated with 2,4-dinitrophenylhydrazine followed by the analysis of the formed hydrazones by HPLC. The present work proposes the use of polypropylene hollow porous capillary fibers to achieve efficient CH(2)O collection. The Oxyphan fiber (designed for blood oxygenation) was chosen for this purpose because it presents good mechanical resistance, high density of very fine pores and high ratio of collection area to volume of the acceptor fluid in the tube, all favorable for the development of air sampling apparatus. The collector device consists of a Teflon pipe inside of which a bundle of polypropylene microporous capillary membranes was introduced. While the acceptor passes at a low flow rate through the capillaries, the sampled air circulates around the fibers, impelled by a low flow membrane pump (of the type used for aquariums ventilation). The coupling of this sampling technique with the selective and quantitative determination of CH(2)O, in the form of hydroxymethanesulfonate (HMS) after derivatization with HSO(3)(-), by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D) enabled the development of a complete analytical protocol for the CH(2)O evaluation in air.

Simultaneous determination of three surfactants and water in shampoo and liquid soap by ATR-FTIR

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 1900-3000cm(-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.

Automated two‐dimensional separation flow system with electrochemical preconcentration, stripping, capillary electrophoresis and contactless conductivity detection for trace metal ion analysis

This paper describes the automation of a fully electrochemical system for preconcentration, cleanup, separation and detection, comprising the hyphenation of a thin layer electrochemical flow cell with CE coupled with contactless conductivity detection (CE‐C4D). Traces of heavy metal ions were extracted from the pulsed‐flowing sample and accumulated on a glassy carbon working electrode by electroreduction for some minutes. Anodic stripping of the accumulated metals was synchronized with hydrodynamic injection into the capillary. The effect of the angle of the slant polished tip of the CE capillary and its orientation against the working electrode in the electrochemical preconcentration (EPC) flow cell and of the accumulation time were studied, aiming at maximum CE‐C4D signal enhancement. After 6 min of EPC, enhancement factors close to 50 times were obtained for thallium, lead, cadmium and copper ions, and about 16 for zinc ions. Limits of detection below 25 nmol/L were estimated for all target analytes but zinc. A second separation dimension was added to the CE separation capabilities by staircase scanning of the potentiostatic deposition and/or stripping potentials of metal ions, as implemented with the EPC‐CE‐C4D flow system. A matrix exchange between the deposition and stripping steps, highly valuable for sample cleanup, can be straightforwardly programmed with the multi‐pumping flow management system. The automated simultaneous determination of the traces of five accumulable heavy metals together with four non‐accumulated alkaline and alkaline earth metals in a single run was demonstrated, to highlight the potentiality of the system.