Giaan A Alvarez-Romero

Autonomous University of Hidalgo, Santa Cruz Hidalgo, Veracruz-Llave, Mexico

Are you Giaan A Alvarez-Romero?

Claim your profile

Publications (9)22 Total impact

  • Source
    [show abstract] [hide abstract]
    ABSTRACT: A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO(4)(2-) ions is presented. Ppy films were electrochemically polymerized onto a graphite-epoxy resin electrode. Experimental current density transients (j-t) were obtained for three different potentiometric behaviors: anionic, cationic, and a combination. Theoretical models were used to fit the experimental j-t data to determine the nucleation and growth processes controlling the polymer synthesis. It was encountered that, in all cases, pyrrole electropolimerization involves two concomitant processes, namely, a Ppy diffusion limited multiple 3D nucleation and growth and pyrrole electro-oxidation on the growing surface of the Ppy nuclei. SEM analysis of the electrodes surfaces reveals that Ppy deposition occurred over most of the electrode surface by multiple nucleation of hemispheres, as the theoretical model used for the analysis of the current transients required. Hemispherical particles formed the polymeric film displaying different sizes. The order for the particle size was as follows: anionic > anionic-cationic > cationic. These results are congruent with those obtained by theoretical analysis of the corresponding current transients. Analysis of the impedance measurements recorded on the anionic Ppy film, immersed in an aqueous solution with different sulfate ion concentrations evidenced that SO(4)(2-) ions diffuse through the Ppy film provoking a decrease of its electrical resistance and an increase of its dielectric constant. From the Warburg impedance coefficient, the sulfate coefficient of diffusion in the Ppy film was 1.38 x 10(-9) cm(2) s(-1).
    The Journal of Physical Chemistry B 08/2010; 114(30):9737-43. · 3.61 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: This paper reports the development and characterization of a solid state potentiometric sensor for chloride ions, based on doped polypyrrole-graphite-epoxy composite. The optimum mixture proportion found for polypyrrole:graphite was 60 : 40 meanwhile a 50 : 50 proportion was used for the polypyrrol+graphite:epoxy mixture. The stabilization time was approximately 16 min, while the response times varied within 2 and 23 s. The sensor displayed a sensitivity of 58 mV/decade [Cl−], and 3×10−6 M detection limit. The selectivity coefficients showed a greater selectivity to that reported for commercial-type sensors. The statistical analysis for chlorides' determination in commercial saline serums did not show significant differences respect to data reported by the manufacturers.
    Electroanalysis 06/2010; 22(14):1650 - 1654. · 2.82 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A selective membrane for direct quantification of saccharinate ion based on a polypyrrole-doped membrane is developed. The membrane is electrochemically prepared using stainless steel as working electrode. Potentiostatic variables for membrane growing such as pyrrole concentration, saccharinate concentration, applied potential and deposition time are optimized in order to maximize sensitivity. The optimized membrane was analytically characterized by means of calibration curves, the detection limit was found to be 3.6×10−4molL−1 and the quantification limits were found between 5×10−4molL−1 and over 1molL−1. Selectivity of the membrane is evaluated for different inorganic anions, resulting in the following selectivity coefficients: pKSaccharinate,Citrate=3.4, pKSaccharinate,H2PO4=3.4, pKSaccharinate,HPO42-=3.4 and pKSaccharinate,HPO42-=2.5.These results demonstrate an adequate performance of the proposed selective polypyrrole membrane so it can be considered as an alternative to traditional analytical methods for the direct quantification of saccharin in diverse samples.
    Food Chemistry - FOOD CHEM. 01/2010; 120(4):1250-1254.
  • [show abstract] [hide abstract]
    ABSTRACT: The manufacture and evaluation of a novel sensor built with a composite material, highly selective to nitrate ions using doped polypyrrole as a recognition agent, are presented. When the ratio of recognition agent to graphite was optimized at 1:1, and the sensitivities found closely approached nernstian behavior. The stability times attained were less than 14 min with response times also below 20 s. Batch characterization of the sensor displayed a sensitivity of 57.1 mV/decade of nitrate ion activity (alphaNO3-) and a detection limit of 5.37 x 10(-5) M, which are comparable to those reported for commercial sensors. Evaluation of the selectivity coefficients showed high affinity to nitrate ion, superior to that of commercial sensors and others reported in the literature. The composite material gives the sensor a prolonged service life with the added capability of allowing the regeneration of its active surface. Coupling the sensor and a solid state, composite-type, reference electrode to a flow injection analysis system (FIA) permitted to achieve an effective overall assessment of the system. A nitrate determination test was conducted on real samples. A comparison of the results obtained, either with stationary measurements or with FIA, indicated that there were no significant differences from the values from manufacturer's specifications.
    Analytical and Bioanalytical Chemistry 03/2007; 387(4):1533-41. · 3.66 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: This work studied the process of electrochemical formation of polypyrrole, Ppy, over a graphite–epoxy resin composite electrode in the presence of different anions: DS−, NO3− and Cl−. It was shown by means of AFM that the morphological characteristics and the formation kinetics of the Ppy deposit, from analysis of experimental current density transients, are strongly dependent on the nature of the anion present. It was found that for all cases, the formation mechanism involves the simultaneous presence of adsorption and 3D nucleation, limited by diffusion of the different pyrrole oligomer species, processes.
    Applied Surface Science - APPL SURF SCI. 01/2006; 252(16):5783-5792.
  • [show abstract] [hide abstract]
    ABSTRACT: An Ag/AgCl solid-state reference electrode is developed by means of a graphite–AgCl–Silver dag-epoxy resin composite. The response of the composite reference electrode (CRE) to chloride ions is evaluated; a linear non-nernstian response is observed associated to the following equation E = −15.15 (±1.10) − 44.05 (±0.38) log[Cl−]. Comparing the CRE's response potential versus a saturated commercial Ag/AgCl reference in KCl 0.1 M, a mean of 40.7 ± 0.4 mV of the distribution of potential versus time data is observed over a period of 1 h. The performance of the CRE as reference for a glass membrane electrode by means of direct pH measurements and quantitative determination of acids by acid–base titrations is evaluated obtaining statistically stable, precise and exact results compared with those obtained using a combined glass electrode. The typical cylindrical configuration of the CRE is changed to adapt it to a FIA system for the determination of ammonium ion, obtaining a sensitivity 50.30 ± 0.26 mV/log[NH4+] and a linear range 8.5 × 10−5 to 0.1 M, which are analytical parameters statistically equivalent to those presented by the classical determination system.
    Sensors and Actuators B: Chemical. 01/2005;
  • [show abstract] [hide abstract]
    ABSTRACT: An amperometric tubular cell involving composite biosensors for the determination of beta-d-glucose in a flow injection analysis (FIA) system is proposed. Diverse configurations and parameters are evaluated to improve the system's response. The configuration producing less noise resulted when the biosensor was located closer to the auxiliary electrode, which also required coupling both electrodes within the system under a continuous flow regime. Further, we report on the influence of the active area of the biosensor and of the flow rate used. Statistical analyses of the data revealed two regions with a linear response range for the determination of beta-d-glucose, with a detection limit of 4.7 x 10(-4) M and in the low concentration region a sensitivity of 17.46 +/- 0.12 microAM(-1). At the beta-d-glucose concentrations studied there was no evidence of enzymatic saturation. An increment on the ionic strength of the sample and carrier passing through the analysis system decreases its sensitivity. The reproducibility of the analytical system in terms of its standard deviation was 2.9% with a 95% confidence level, having a lifetime that lasted at least 100 days. beta-d-Glucose was determined in different commercial medical glucose-containing solutions, the experimental results are in good agreement with those reported by the manufacturer.
    Biosensors and Bioelectronics 05/2004; 19(9):1057-65. · 5.44 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Potentiostatic polymerization of polypyrrole doped with dodecylsulfate anion (DS−) was carried out in situ over a tubular composite (graphite-epoxy resin) support in order to develop a potentiometric DS− sensor (TISE) suitable for flow injection analysis (FIA). The sensibility of the TISE was maximized using the SIMPLEX algorithm in terms of the concentration of the pyrrole monomer, the concentration of DS−, the potential imposed and polymerization time. Response times between 2 and 4 minutes were observed. The analytical parameters obtained with the flow system were compared with those obtained in batch studies. In both, flow and batch analysis, potential vs. DS− concentration curves displayed two linear regions with different slopes. Flow analysis for DS− ion brings a total linear range of 1.58×10−5 M to 3.88×10−3 M with a maximum sensibility of 36.4 mV/concentration decade, meanwhile in batch studies the total linear range found was of 6.31×10−6 M to 1.0×10−3 M with a maximum sensibility of 54.49 mV. The flow system response pH range was from 5 to 8. The reproducibility in terms of the relative error of the mean of different experiments was 1.58%. Two salient features of the system designed and built are worthy of mention: the sensor presented high selectivity to the dodecyl sulfate ion as compared to other inorganic anions including other anionic surfactants. The sensor lifetime in the FIA system by means of the sensibility changes was found to be of approximately four months.
    Electroanalysis 03/2004; 16(15):1236 - 1243. · 2.82 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The traditional method of calculating equilibrium constants in glacial acetic acid medium was developed by Kolthoff and Bruckenstein in 1957; thenceforth, and even presently, few alternatives have been made available to undertake such studies. This paper presents the results obtained with the use of the program Superquad to assess the equilibrium constants of various bases and their protonated perchlorate salts in glacial acetic media. A model of formation equilibria is proposed and fed into the program, considering the species present during an acid-base titration. The calculations of the equilibrium constants using Superquad for pyridine and diethylamine are statistically in agreement with those reported in the literature, (for pyridine: pK(B)=5.98+/-0.02, pK( PyHClO4)=5.47+/-0.02 and for diethylamine pK(B)=5.52+/-0.04, pK( DietHClO4)=4.52+/-0.07). With the use of Superquad, the values found for the aniline were pK(B)=6.95+/-0.06 and pK( AnilHClO4)=4.89+/-0.06.
    Analytical and Bioanalytical Chemistry 04/2003; 375(6):826-30. · 3.66 Impact Factor