Three models using partial least squares regression of near infrared reflectance spectroscopy were developed for the first time to evaluate the concentration of total alkaloids as nicotine, total nitrogen and total ash in powdered samples of Cuban cigar tobacco. They had lower standard error of cross-validation (SECV) and standard error of prediction (SEP) than those using: (1) principal components regression; (2) multiple linear regression and (3) other partial least squares models previously published for this and other tobacco types. SECV values in mass fraction units were: 0.0010, 0.0011 and 0.0048, respectively. The coefficients of determination (R2) in calibration were: 0.99, 0.94 and 0.96, respectively. Standard error of prediction values were: 0.0011, 0.0012 and 0.0049, respectively. The r2 obtained when comparing the predicted values using the validation set with the reference data was nearly the same as in calibration. The equation for total alkaloids as nicotine was good for quantification, and for process control, development and applied research according to the quotients range/standard error of prediction and standard deviation/standard error of prediction, respectively. Equations for the other analytes were as good as the one for alkaloids, but suitable only for screening purposes. Joint F-tests on the regression coefficients from ordinary least squares and iterative reweighted least squares fittings among predicted and reference data indicated slopes and intercepts enclosing 1 and 0, respectively. The relative systematic errors between the near infrared spectroscopy predicted values and the reference methods are close to the same figures reported previously for traditional analytical procedures under intermediate precision and reproducibility conditions; hence, the models are suitable for this industrial context.

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Recebido em 4/4/13; aceito em 1/7/13; publicado na web em 9/8/13 PORTABLE GAS DATA LOGGER BASED ON TEMPERATURE MODULATION OF A SINGLE MOS COMMERCIAL SENSOR. A simple, portable and low-cost system for odor detection was developed using a single MOS commercial sensor and a microcontroller. The temperature modulation technique was implemented applying a DC signal pulse to the sensor heater by a bipolar transistor. Two odorant profiles, ethanol and acetic acid vapors, were obtained and distinguished based on their amplitude versus time responses. Response for acetic acid was not reported by the sensor manufacturer. An ethanol vapor calibration curve was also obtained. Experimental data showed a potential behavior according to the theoretical equation of the MOS sensors. Values of logK=0.457 and α=-0.213 for a 95% confidence level were obtained.Keywords: portable odorant data logger; odor detection; embedded system. INTRODUCCIÓNDesde sus orígenes el hombre ha utilizado su sentido del olfato para diagnosticar enfermedades, comprobar el estado de los alimentos o identificar peligros.1 Con el desarrollo científico-técnico y debido a la necesidad de realizar estas medidas en ambientes nocivos, de difícil acceso o para obtener resultados más precisos y rápidos, se han desarrollado instrumentos que sustituyen o apoyan al hombre en estas tareas. Actualmente, se reportan diferentes tipos de sistemas para mediciones de gases y vapores, que incluyen desde los cromatógrafos gaseosos, analizadores de gases y alcoholímetros hasta otros métodos que emplean la propia nariz humana como los olfatómetros y escentómetros. 2Una alternativa interesante frente a estos equipos de laboratorio son los instrumentos conocidos como sistemas de olfato electrónico o narices electrónicas.3 Las aplicaciones de estos instrumentos son variadas y se reporta su empleo en el campo de la industria alimenticia, 4 diagnóstico médico 5 y detección de parámetros medioambientales 6,7 así como en la industria aeroespacial, cosmética y la rama militar y otras. 8,9 En particular en la industria vinícola se conocen investigaciones que emplean estos sistemas para detectar y reconocer el grado de envejecimiento de vinos 10 y detectar la presencia de ácido acético. 11También se conocen aplicaciones para discriminar muestras de vinos con diferentes concentraciones de etanol. 12Estos sistemas pueden utilizar sensores de diferente naturaleza como los sensores de Metal-Oxido-Semiconductor (MOS), los basados en materiales poliméricos, piezoeléctricos, ópticos, MOSFETs y otros.3 No obstante, en una amplia cantidad de trabajos se reporta el empleo de los sensores comerciales MOS basados en SnO 2 .3 Esto se debe a su disponibilidad en el mercado, relativo bajo costo y que no requieren de circuitos acondicionadores complejos. Actualmente existen empresas que comercializan este tipo de sensores como la casa Figaro de Japón. 13Se ha reportado que la respuesta transitoria de los sensores es más rica en información a la hora de realizar el análisis.14 Esta respuesta puede obtene...

Some acquired experiences concerning the teaching of Chemical Metrology in Latin-America for almost fifteen years are presented. They include postgraduate and undergraduate activities developed in seven countries of this continent. The combination of theoretic and practical activities and the sequence of learning from metrological, statistical and chemometrical backgrounds up to practical activities in personal computers are basic and motivate the learning process. Care is taken in order to promote the metrological approach and thinking in Analytical Chemistry. The learning of computing techniques plays an important role, combining graphic and numerical techniques for data analysis. The role of examples during the teaching process is analyzed and recognized. The introduction of a general model of errors permits to approach different topics on a metrological basis. Similarly, linking of performance characteristics of analytical procedures and validation concepts is essential. The understanding of traceability prepares students for organizational actions. Proper understanding of interlaboratory studies is attained on a practical basis. The metrological approach of uncertainty based on the Theory of Errors permits to develop the topic. A better comprehension of written standards is obtained from practical examples. Undergraduate students acquire a basic metrological knowledge very well. Recommendations for undergraduate and postgraduate programs are pointed out.