Ibuprofen is a widely used pharmaceutical because of its therapeutic properties; it is considered a safe medicament, thus it does not require medical prescription to be sold. However, in order to ensure consumer's health it is indispensable that the pharmaceutical industry relies on analytic methods for its quantification. Potentiometry has proven to be a successful technique using second type electrodes, which in agreement with Nernst's equation can detect anions activity. On consideration of this, this research work presents the development of a second type electrode based on the silver/silver ibuprofenate pair. This involved modifying a pure silver wire using a sodium ibuprofenate solution, to obtain the redox pair. The following analytic parameters were obtained with the aid of the modified electrode: a sensitivity of -0.049 V decade [ibuprofenate]-1, 8 µmol L-1 for the detection limit and a quantification limit of 1.2 µmol L-1. The repeatability value in terms of the relative standard deviation was 5.9%. After performing an interferences analysis using some ions and excipients, it was corroborated that there were none, thus allowing appropriate quantification on a real sample.

In the present work the development of an amperometric transducer in order to build a free cholesterol biosensor in planar configuration is reported. The one single use disposable biosensors were constructed by screen printing process which is compatible with automated methodologies of production. Based in the incorporation of tetracyanoquinodimethane (TCNQ), Prussian blue (PB) or ferrite (Fe3O4) as mediator or electrocatalytic agent, three types of electrochemical transducers were evaluated. The cholesterol biosensors require a sample volume of 7.2 µL, exhibits good reproducibility and selectivity and cover a lineal answer of 2-16 mM with detection limits from 0.3 to 1.6 mM. The characteristics of biosensors are satisfactory for the decentralized analysis of the lipid in blood since enclose the range of clinical interest (3.5-6.5 mM).

En el presente trabajo se reporta el desarrollo de un transductor amperométrico con la finalidad de construir un biosensor de colesterol en configuración plana. Basados en la incorporación de tetracianoquinodimetano (TCQN), azul de Prusia (AP) o ferrita (Fe3O4) como mediador o agente electrocatalítico, fueron evaluados tres tipos de transductores electroquímicos. Los biosensores desechables de un solo uso fueron fabricados por serigrafía, la cual es compatible con metodologías automatizadas de producción. Los biosensores de colesterol requieren un volumen de muestra de 7.2 µL, exhiben buena reproducibilidad y selectividad y cubren una linealidad de 2-16 mM con un límite de detección de 0.3 a 1.6 mM. Las características de los biosensores son satisfactorias para el análisis descentralizado del lípido en sangre ya que cubren el intervalo de interés clínico (3.5-6.5 mM).

In this work a description of different methods and strategies for the teaching of experimental general and analytical chemistry can be found. These didactic methods and strategies were applied in Analytical Chemistry Section of Escuela Nacional de Estudios Profesionales, Campus Cuautitlán, from Universidad Nacional Autónoma de México, and in the Basic Sciences and Engineering Division of Universidad Autónoma Metropolitana, Campus Iztapalapa, between 1978 and 2004. The methods and strategies were effective for the teaching of experimental chemistry and the development of abilities to solve specific problems by experimental path; nevertheless, the new generations have difficulties to learn in the same way; then new methods and strategies for the teaching of experimental chemistry should be developed for the students of the 21st Century.

En este trabajo se presenta una descripción de los diferentes métodos y estrategias empleadas para la enseñanza de la química general y analítica. Estos métodos didácticos y estrategias se aplicaron en la sección de Química Analítica de la Escuela Nacional de Estudios Profesionales, Campus Cuautitlán, de la Universidad Nacional Autónoma de México, y en la División de Ciencias Básicas e Ingenierías de la Universidad Autónoma Metropolitana, Campus Iztapalapa, entre 1978 y 2004. Los métodos y estrategias fueron efectivos para la enseñanza experimental de la química y para el desarrollo de habilidades para resolver problemas específicos por la vía experimental; no obstante, las nuevas generaciones han tenido problemas para aprender de esa manera, así que deben generarse nuevos métodos y estrategias para la enseñanza experimental de la química del siglo XXI.

The rigorous treatment of the equilibrium state of a monoprotic acid solution (or a monoprotic base) is presented in order to justify the simplifications that permit the teaching hall presentation with a worksheet.

Se presenta el tratamiento riguroso del estado de equilibrio de una disolución de un ácido (o una base) monoprótico para justificar las simplificaciones que permiten la enseñanza en el aula utilizando una hoja de cálculo.

The structure of analytical chemistry designed by Prof. Gaston Chariot in France, about 1940, begins with a very simple model of chemical reaction, understood as a process in which a donor gives only one kind of particles to an acceptor. When this model is assimilated by the student then the study of chemical reactions that exchange two or more type of particles is presented. Gradually the model incorporates the study of more and more complex reactions and processes, as precipitation, redox, non aqueous solvents, and separations, among others. This approach permits to plan and resolve complex problems of analytical and industrial chemistry. In the present work we show the analogies of the analytical chemistry proposed by G. Charlot and the principles of constructivism applied nowadays to the teaching of sciences.

A quantitative methodology to determine formation constants that takes into consideration the 27Al-NMR signals of Al(III)-H2O systems has been analyzed, where area fractions beneath the peaks recorded were associated with the corresponding species fractions. The values of the formation constants were compared with the model obtained by potentiometric studies. In agreement with previous reports, the -log*β values obtained by NMR and potentiometry, at 0.020 M ≤ [Al(III)]total ≤ 0.500 M are 12.96 ± 0.02 for Al(OH)3, 13.50±0.02 for Al3(OH)4(5+), and 109.70±0.09 for Al13(OH)32(7+), by assuming that Al(OH)²+ has a value of 5.29. Additionally the equilibrium constant values obtained allowed fitting of the conductimetry titrations in the 6.00(10-³) M ≤ [Al(III)]total ≤ 0.120 M. The algorithm presented in this work gives a support to establish that the area fractions of NMR signals are proportional to the species concentration fractions.

Una metodología para determinar constantes de formación por medio de señales de 27Al-NMR para sistemas Al(III)-H2O se aplicó, en donde las fracciones de área bajo los picos se asoció con las fracciones de las especies correspondientes. Los valores de constantes de formación obtenidos de esta forma se compararon con los obtenidos con estudios potenciométricos. Los valores obtenidos de -log*β obtenidos por NMR y potenciometría a partir de sistemas con 0.020 M ≤ [Al(III)]total ≤ 0.500 M son 12.96 ± 0.02 para Al(OH)3, 13.50 ± 0.02 para Al3(OH)4(5+), y 109.70 ± 0.09 para Al13(OH)32(7+), considerando que Al(OH)2+ tiene un valor de 5.29, y concuerdan con reportes previos. Además, estos valores de constantes de equilibrio permiten ajustar curvas de valoración conductimétricas, en las cuales 6.00(10-³) M ≤ [Al(III)]total ≤ 0.120 M. Este algoritmo da fundamento para establecer que las fracciones de área de las señales de NMR son proporcionales a las fracciones de concentración de las especies.