Silver, zinc, and copper nanoparticles were reductively crystallized on thymine-containing single... more Silver, zinc, and copper nanoparticles were reductively crystallized on thymine-containing single-stranded DNA decanucleotides, in aqueous solutions containing the corresponding metal ions and sodium borohydride, at 4 °C, pH 11.8, and 15 mM of NaCl. Iron nanoparticles were not formed under these conditions. Formation of aggregates was monitored by UV-Vis spectrophotometry, and characterized by scanning electron microscopy and dynamic light scattering. The absorption spectra for most Ag + -containing samples showed a major band centered around 425 nm and a shoulder between 500 and 600 nm, indicative of the presence of silver particles in a wide size distribution, in the 0.1–5 μm range. This was verified by micrographs and size distribution observed in scattering profiles. Silver-particle morphology indicates formation of cubic structures instead of spherical geometries. For the case of zinc and copper nanoparticles, quasi-spherical structures of approximately 100 nm were crystallized along the DNA chains by reduction reaction, and then released to the bulk solvent. Thymine residues show a higher effectiveness in nucleation of metallic cations in comparison to other DNA nucleobases, particularly in their deprotonated form, at high pH values. Adenines flanking central runs of deprotonable bases in the model oligonucletide chain affect the production of silver crystals on the DNA decamers. pH value and NaCl concentration have a significant effect on the production of silver particles, as alkaline and moderate-ionic-strength conditions are required to crystallize such structures. The tuning of size and morphology of metallic nanoparticles by the proper choice of oligonucleotide sequence and physical conditions may have interesting applications in the field of nanobiotechnology.
According to the experience of the successful implementation of proficiency tests (PT) by using t... more According to the experience of the successful implementation of proficiency tests (PT) by using the certified reference value as the assigned value, a new scheme of evaluation is presented by suggesting the use of the uncertainty associated with the certified value. The technical performance of laboratories is evaluated by the parameter quadratic mean error (QME), which is the square root
IOP Conference Series: Materials Science and Engineering, 2016
The main goal of method validation is to demonstrate that the method is suitable for its intended... more The main goal of method validation is to demonstrate that the method is suitable for its intended purpose. One of the advantages of analytical method validation is translated into a level of confidence about the measurement results reported to satisfy a specific objective. Elemental composition determination by wavelength dispersive spectrometer (WDS) microanalysis has been used over extremely wide areas, mainly in the field of materials science, impurity determinations in geological, biological and food samples. However, little information is reported about the validation of the applied methods. Herein, results of the in-house method validation for elemental composition determination by WDS are shown. SRM 482, a binary alloy Cu-Au of different compositions, was used during the validation protocol following the recommendations for method validation proposed by Eurachem. This paper can be taken as a reference for the evaluation of the validation parameters more frequently requested to get the accreditation under the requirements of the ISO/IEC 17025 standard: selectivity, limit of detection, linear interval, sensitivity, precision, trueness and uncertainty. A model for uncertainty estimation was proposed including systematic and random errors. In addition, parameters evaluated during the validation process were also considered as part of the uncertainty model.
The standardization of secondary electrolytic conductivity cells requires the use of a certified ... more The standardization of secondary electrolytic conductivity cells requires the use of a certified reference material. The accepted certification method involves electrochemical impedance spectroscopy (EIS) to estimate the material's solution resistance. This method normally assumes that the impedance's imaginary component can be neglected; and hence, the measured impedance approximates the real impedance. Thus, a linear extrapolation of the impedance versus the period (inverse frequency) yields solution resistance. However, experimental impedance data usually do not exhibit a linear behavior over the spectra of frequency, which strongly suggest that the ideal capacitive assumption may not strictly apply. To account for the observed nonlinear behavior, we have proposed to introduce the concept of a constant phase element (CPE) to the analysis of impedance. This approach leads to the development of a relationship that improves the fitting of experimental data and improves the accuracy of the estimation, by establishing a critical frequency where extrapolation should be done. Finally, we are presenting simulated results to demonstrate how sizeable capacitive effects can influence the determination of solution resistance, and a final analysis to estimate the impact on constant cell or electrolytic conductivity values.
Magnetic iron oxide nanoparticles of controlled size distribution were electrochemically synthesi... more Magnetic iron oxide nanoparticles of controlled size distribution were electrochemically synthesized applying a dissymmetric pattern of potential pulses to iron-based electrodes in aqueous media. The best pattern was determined through a design of experiments based on a previous voltammetric study. The applied method conveys an optimization of previous methods which employed direct or symmetric alternate potentials. XRD results indicate that magnetite phase is favored to anodic potentials larger-0.2 V versus SSE. TEM images show quasi spherical particles with size ranging from 10 to 50 nm, depending on the synthesis conditions, which agrees with size estimated from diffractograms. EDS indicate that the electrolyte is not totally eliminated by washing although its content is lower than 1 %.
A partir del año 2000 se incremento en México la demanda por la acreditación de los laboratorios ... more A partir del año 2000 se incremento en México la demanda por la acreditación de los laboratorios analíticos de ensayos y calibraciones bajo la plataforma de la norma ISO-17025. La Norma ISO 17025 es aplicable a todas las organizaciones que realizan ensayos y/o calibraciones. Éstas incluyen, por ejemplo, los laboratorios de primera, segunda y tercera parte, y laboratorios donde el ensayo y/o la calibración hacen parte de la inspección y certificación del producto.
The main goal of method validation is to demonstrate that the method is suitable for its intended... more The main goal of method validation is to demonstrate that the method is suitable for its intended purpose. One of the advantages of analytical method validation is translated into a level of confidence about the measurement results reported to satisfy a specific objective. Elemental composition determination by wavelength dispersive spectrometer (WDS) microanalysis has been used over extremely wide areas, mainly in the field of materials science, impurity determinations in geological, biological and food samples. However, little information is reported about the validation of the applied methods. Herein, results of the in-house method validation for elemental composition determination by WDS are shown. SRM 482, a binary alloy Cu-Au of different compositions, was used during the validation protocol following the recommendations for method validation proposed by Eurachem. This paper can be taken as a reference for the evaluation of the validation parameters more frequently requested to get the accreditation under the requirements of the ISO/IEC 17025 standard: selectivity, limit of detection, linear interval, sensitivity, precision, trueness and uncertainty. A model for uncertainty estimation was proposed including systematic and random errors. In addition, parameters evaluated during the validation process were also considered as part of the uncertainty model.
La metrología está presente en todos los ámbitos de las ciencias, y la trazabilidad metrológica g... more La metrología está presente en todos los ámbitos de las ciencias, y la trazabilidad metrológica garantiza que los resultados obtenidos en un laboratorio o empresa puedan ser comparables en cualquier parte del mundo. En electroquímica, es poco lo que se ha incluido la metrología. Se presentan ideas para introducir la metrología en los laboratorios de electoquímica del país.
Silver, zinc, and copper nanoparticles were reductively crystallized on thymine-containing single... more Silver, zinc, and copper nanoparticles were reductively crystallized on thymine-containing single-stranded DNA decanucleotides, in aqueous solutions containing the corresponding metal ions and sodium borohydride, at 4 °C, pH 11.8, and 15 mM of NaCl. Iron nanoparticles were not formed under these conditions. Formation of aggregates was monitored by UV-Vis spectrophotometry, and characterized by scanning electron microscopy and dynamic light scattering. The absorption spectra for most Ag + -containing samples showed a major band centered around 425 nm and a shoulder between 500 and 600 nm, indicative of the presence of silver particles in a wide size distribution, in the 0.1–5 μm range. This was verified by micrographs and size distribution observed in scattering profiles. Silver-particle morphology indicates formation of cubic structures instead of spherical geometries. For the case of zinc and copper nanoparticles, quasi-spherical structures of approximately 100 nm were crystallized along the DNA chains by reduction reaction, and then released to the bulk solvent. Thymine residues show a higher effectiveness in nucleation of metallic cations in comparison to other DNA nucleobases, particularly in their deprotonated form, at high pH values. Adenines flanking central runs of deprotonable bases in the model oligonucletide chain affect the production of silver crystals on the DNA decamers. pH value and NaCl concentration have a significant effect on the production of silver particles, as alkaline and moderate-ionic-strength conditions are required to crystallize such structures. The tuning of size and morphology of metallic nanoparticles by the proper choice of oligonucleotide sequence and physical conditions may have interesting applications in the field of nanobiotechnology.
According to the experience of the successful implementation of proficiency tests (PT) by using t... more According to the experience of the successful implementation of proficiency tests (PT) by using the certified reference value as the assigned value, a new scheme of evaluation is presented by suggesting the use of the uncertainty associated with the certified value. The technical performance of laboratories is evaluated by the parameter quadratic mean error (QME), which is the square root
IOP Conference Series: Materials Science and Engineering, 2016
The main goal of method validation is to demonstrate that the method is suitable for its intended... more The main goal of method validation is to demonstrate that the method is suitable for its intended purpose. One of the advantages of analytical method validation is translated into a level of confidence about the measurement results reported to satisfy a specific objective. Elemental composition determination by wavelength dispersive spectrometer (WDS) microanalysis has been used over extremely wide areas, mainly in the field of materials science, impurity determinations in geological, biological and food samples. However, little information is reported about the validation of the applied methods. Herein, results of the in-house method validation for elemental composition determination by WDS are shown. SRM 482, a binary alloy Cu-Au of different compositions, was used during the validation protocol following the recommendations for method validation proposed by Eurachem. This paper can be taken as a reference for the evaluation of the validation parameters more frequently requested to get the accreditation under the requirements of the ISO/IEC 17025 standard: selectivity, limit of detection, linear interval, sensitivity, precision, trueness and uncertainty. A model for uncertainty estimation was proposed including systematic and random errors. In addition, parameters evaluated during the validation process were also considered as part of the uncertainty model.
The standardization of secondary electrolytic conductivity cells requires the use of a certified ... more The standardization of secondary electrolytic conductivity cells requires the use of a certified reference material. The accepted certification method involves electrochemical impedance spectroscopy (EIS) to estimate the material's solution resistance. This method normally assumes that the impedance's imaginary component can be neglected; and hence, the measured impedance approximates the real impedance. Thus, a linear extrapolation of the impedance versus the period (inverse frequency) yields solution resistance. However, experimental impedance data usually do not exhibit a linear behavior over the spectra of frequency, which strongly suggest that the ideal capacitive assumption may not strictly apply. To account for the observed nonlinear behavior, we have proposed to introduce the concept of a constant phase element (CPE) to the analysis of impedance. This approach leads to the development of a relationship that improves the fitting of experimental data and improves the accuracy of the estimation, by establishing a critical frequency where extrapolation should be done. Finally, we are presenting simulated results to demonstrate how sizeable capacitive effects can influence the determination of solution resistance, and a final analysis to estimate the impact on constant cell or electrolytic conductivity values.
Magnetic iron oxide nanoparticles of controlled size distribution were electrochemically synthesi... more Magnetic iron oxide nanoparticles of controlled size distribution were electrochemically synthesized applying a dissymmetric pattern of potential pulses to iron-based electrodes in aqueous media. The best pattern was determined through a design of experiments based on a previous voltammetric study. The applied method conveys an optimization of previous methods which employed direct or symmetric alternate potentials. XRD results indicate that magnetite phase is favored to anodic potentials larger-0.2 V versus SSE. TEM images show quasi spherical particles with size ranging from 10 to 50 nm, depending on the synthesis conditions, which agrees with size estimated from diffractograms. EDS indicate that the electrolyte is not totally eliminated by washing although its content is lower than 1 %.
A partir del año 2000 se incremento en México la demanda por la acreditación de los laboratorios ... more A partir del año 2000 se incremento en México la demanda por la acreditación de los laboratorios analíticos de ensayos y calibraciones bajo la plataforma de la norma ISO-17025. La Norma ISO 17025 es aplicable a todas las organizaciones que realizan ensayos y/o calibraciones. Éstas incluyen, por ejemplo, los laboratorios de primera, segunda y tercera parte, y laboratorios donde el ensayo y/o la calibración hacen parte de la inspección y certificación del producto.
The main goal of method validation is to demonstrate that the method is suitable for its intended... more The main goal of method validation is to demonstrate that the method is suitable for its intended purpose. One of the advantages of analytical method validation is translated into a level of confidence about the measurement results reported to satisfy a specific objective. Elemental composition determination by wavelength dispersive spectrometer (WDS) microanalysis has been used over extremely wide areas, mainly in the field of materials science, impurity determinations in geological, biological and food samples. However, little information is reported about the validation of the applied methods. Herein, results of the in-house method validation for elemental composition determination by WDS are shown. SRM 482, a binary alloy Cu-Au of different compositions, was used during the validation protocol following the recommendations for method validation proposed by Eurachem. This paper can be taken as a reference for the evaluation of the validation parameters more frequently requested to get the accreditation under the requirements of the ISO/IEC 17025 standard: selectivity, limit of detection, linear interval, sensitivity, precision, trueness and uncertainty. A model for uncertainty estimation was proposed including systematic and random errors. In addition, parameters evaluated during the validation process were also considered as part of the uncertainty model.
La metrología está presente en todos los ámbitos de las ciencias, y la trazabilidad metrológica g... more La metrología está presente en todos los ámbitos de las ciencias, y la trazabilidad metrológica garantiza que los resultados obtenidos en un laboratorio o empresa puedan ser comparables en cualquier parte del mundo. En electroquímica, es poco lo que se ha incluido la metrología. Se presentan ideas para introducir la metrología en los laboratorios de electoquímica del país.
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