En este trabajo, se construyo y evaluo la respuestaelectroquimica de un electrodo de membran aheterogenea selectivo a cimetidina incorporando un complejo de par ionicocimetidina - acidofosfotungstico (CMT-AFT) como materialelectroactivo, dibutilftalato (DBP) comoplastificante y policloruro de vinilo (PVC) comosoporte. Se optimizaron los parametros que afectan el funcionamiento del electrodo, tales como: composicion de la membrana, concentracion de la disolucion interna y pH. El electrodo mostro una respuesta rapida y estable con un intervalo lineal desde 1,00x10-4 hasta 1,00x10-1 M encimetidina al serutilizadoen un rango de pH entre 2,73 – 5,00 unidades, unapendiente de 56,63 ± 0,06 mV pordecada y un limite de deteccion de 3,98x10-5 M a 25,00 ± 1,00 ° C. El electrodoexhibiounabuenaselectividad para la cimetidina con respecto a un numero de ionesinorganicoscomunes. El electrodo de membranafueaplicadoen ladeterminacion de cimetidina en formulacione sfarmaceuticas mediante potenciometria directa obteniendose resultados que no difieren significativamente con los declarados por las empresasfarmaceuticas.

El objetivo general de la presente investigacion fue la validacion de un metodo analitico para la determinacion espectrofotometrica de fenoles totales en muestras de agua naturales empleando la microextraccion con gota directamente suspendida. Se determinaron los parametros de calidad del metodo analitico Posteriormente se procedio a evaluar la veracidad del mismo mediante la aplicacion del estudio de efecto matriz y las pruebas de recuperacion. Finalmente, los parametros obtenidos fueron comparados con los reportados por el metodo estandar 5530C. Se encontro que la linealidad del metodo fue de 99,91%, limite de deteccion y cuantificacion de 0,2380 y 0,7932 µg/L respectivamente, un rango dinamico lineal comprendido entre 0,2380-350 µg/L, y la desviacion estandar relativa obtenida en el estudio de precision se encontro entre 1,20 y 4,25 %. En el estudio de efecto matriz se evidencio que no existe una diferencia significativa entre las pendientes de la curva de calibrado y adicion patron. En los estudios de recuperacion sobre las muestras de agua del lago se obtuvieron excelentes porcentajes comprendidos entre el 98,92-101,89 %. La comparacion realizada permitio evidenciar las ventajas que presenta el metodo validado con respecto al metodo estandar permitiendo una reduccion significativa de los volumenes de solvente y muestra necesarios para la determinacion de fenoles. Palabras clave: Fenoles totales; determinacion espectrofotometrica; microextraccion con gota directamente suspendida; metodo analitico. Abstract The general objective of this research was the validation of an analytic method for the spectrophotometric determination of total phenols in natural water using directly suspended droplet microextraction. Quality parameters of the analytic method were obtained by the construction of the calibration curve. Afterwards, the veracity of the method was evaluated through application of the matrix study effect and recovery tests. Finally the obtained parameters were compared to the ones reported by the standard method. The method’s linearity was found to be 99.91%, while the detection and quantification limits were of 0.2830 and 0.7937 µg/L respectively; the linear dynamic range was found to be between 0.2380-350 µg/L and the relative standard deviation between 1.20 and 4.25%. During the matrix effect study it was evidenced that there is no significant difference between the slopes of the calibration and the standard addition curve. In the recovery studies over the samples of water from the lake, excellent percentages were obtained comprehended between 98.92-101.89%. The comparison allowed to evidence the advantages that the validated method presents over the standard method permitting a significant reduction in the volumes of solvent and samples necessary for the determination of phenols. Keywords: Total phenols; spectrophotometric determination; directly suspended droplet microextraction; analytic method.

The presence and persistence of drugs in natural waters is an issue of high environmental interest, because of the biological activity of these emergent contaminants. In this work a gas chromatography-mass spectrometry analytical method was applied to a persistence study of ibuprofen, ketoprofen, diclofenac and clofibric acid in raw and lake water samples stored at room temperature under sunlight and dark conditions. Pharmaceuticals degradation follow a pseudo first order kinetic and their half-lives calculated in every experimental condition. The most rapid degradation rate was observed in non-filtered open recipients samples exposed to sunlight, where environmental factors such as adsorption on particulates, biodegradation and sunlight were present. Under sunlight, ketoprofen was quickly degraded with half-lives from 7.1 to 11.9 hours, while clofibric acid had the higher persistence (t1/2 = 130.7 – 495.1 days).

An analytical method for the determination of diflufenican, mepanipyrim, pretilachlor, and fipronil in water samples was developed using single drop microextraction in the direct immersion mode and gas chromatography–mass spectrometry. A factorial fractionated design of type 26–1 at two levels was performed, to study the influence of experimental variables such as ionic strength, pH, agitation speed, extraction time, drop volume, and sample volume. To establish the optimal conditions for the variables that were significant, a Doehlert design was performed. The optimum conditions of extraction were 1 μL of heptane immersed in 4.0 mL of sample with continuous agitation at 500 rpm for 30 min at room temperature. The developed method proved to have good linearity for the range studied. The detection limits were 0.07 μg L−1 for diflufenican, 0.03 μg L−1 for mepanipyrim, 0.08 μg L−1 for pretilachlor, and 1.39 μg L−1 for fipronil. The method was validated on river water samples, showing the absence of matrix effect and recoveries ranged from 90.1 to 107.8 %. The results show that the method developed is accurate, sensitive, rapid, simple, and low cost, so it is recommended for application in the analysis of these different classes of pesticides in water samples.

A method for determination of trace amounts of the fungicides kresoxim-methyl and trifloxystrobin in water samples, previous single-drop microextraction, was developed using gas chromatography-mass spectrometry. The effects of organic solvent, stirring speed, drop volume, ionic strength, sample volume, extraction time as well as the extraction temperature were studied. Both fungicides were extracted using 2 mu L of n-heptane. The linear concentration range of application was 0.2-10.0 mu g/L (r = 0,998-0,999) for both compounds, with detection limits of 4.0 ng/L for kresoxim-methyl and 7.0 ng/L for trifloxystrobin. The method was validated by analysis of spiked matrix samples. Recovery levels were between 83.0 and 109.6%. In view of its simplicity, low cost and sensitivity, the proposed method is applicable for the quantification of residues of kresoxim-methyl and trifloxystrobin in water samples.

En este trabajo se describe un método de análisis de kresoxim-metil y trifloxystrobin en muestras de agua mediante microextracción con gota suspendida y cromatografía de gases-espectrometría de masa. Se investigó la influencia del disolvente de extracción, velocidad de agitación, fuerza iónica, volumen de muestra, tiempo de extracción, volumen de la gota y temperatura de extracción en la respuesta analítica. Ambos fungicidas fueron extraídos con 2 μL de n-heptano. El método presentó buena linealidad para el intervalo entre 0,2 a 10 μg/L (r = 0,998-0,999). Se encontraron límites de detección de 4,0 ng/L para el kresoxim-metil y 7,0 ng/L para el trifloxis trobin. El método fue validado para muestras de agua encontrándose porcentajes de recuperación entre 83,0- 109,6%. La metodología es sencilla, de bajo costo, adecuada sensibilidad y por consiguiente recomendable para el análisis de residuos de kresoxim-metil y trifloxystrobin en muestras de agua.

A method for the determination of trace amounts of acidic herbicides in water samples was developed. The analytical procedure involves in situ derivatization of analytes to their methyl esters with dimethyl sulfate, sampling using single drop microextraction (SDME) and gas chromatography-mass spectrometry (GC-MS). The effects of pH, ionic strength, extraction time, solvent of extraction as well as derivatization conditions were studied. Methyl esters were extracted using 2 mu L of n-heptane. The response was linearly dependent on the concentration in the range 0.05-10.0 ng mL(-1). Limits of detection were achieved at the level of 1.8-3.0 ng L-1. Derivatization-SDME/GC-MS analysis yielded good precision (RSD between 7.0 and 15.2%). The method was validated by analysis of spiked matrix samples.

Two montmorillonites, SWy-2 (Wyoming, USA) and STx-1 (Texas, USA) (henceforth referenced as SW and ST) were acid activated, pillared with aluminum or iron and then impregnated with Co. Catalysts using the raw clays were also prepared. The synthesized catalysts were characterized by X-ray diffraction, thermal analysis, surface area, acidity determinations and temperature programmed reduction. The catalytic activity was measured using the hydrodesulfurization of thiophene at 350°C. Acid and pillaring treatments increased the surface area, porosity and acidity. In all catalysts, microporosity and mesoporosity were observed. The surface area and porosity of the catalysts were not affected by Co incorporation, however the acidity decreased. The reduction profiles showed the formation of several surface species of cobalt with aluminum and iron in both Al- and Fe-pillared clays. The activity for the hydrodesulfurization of thiophene depended on the chemical properties and textural characteristics of the support. The most active Co catalysts were those supported on acid activated clays (11 and 45% for Co/HSW and Co/HST), followed by those supported on Al-pillared clays (7 and 15% for Co/AlSW and Co/AlST) and Fe-pillared clays (2 and 17% for Co/FeSW and Co/FeST) and on the raw clays, which showed the lowest conversions (2 and 6% for Co/SW and Co/ST).

In this work Co, Mo and CoMo catalysts supported on a montmorillonite clay (STx-1, Texas, USA) in its natural and Al-pillared forms were prepared. These catalysts in their unreduced and reduced forms were tested over the dehydrogenation of ethylbenzene to study the effect of the metal reduction. The catalysts were prepared by impregnation with aqueous solutions of CoCl2·6H2O and (NH4)6Mo7O24·4H2O and characterized by N2 adsorption, X-ray diffraction, temperature programmed reduction and CO chemisorption. The total metal content of cobalt and/or molybdenum was 4 wt.% in the monometallic and bimetallic catalysts, varying the Co–Mo mass ratio in 1:3, 2:2 and 3:1 (Co:Mo atomic ratios of 0.54, 1.63 and 4.84) in the latter. The surface areas of the natural and Al-pillared clays were 72 and 123 m2/g, while the areas of the Co, Mo and CoMo catalysts supported on ST and Al-ST were 48–69 and 77–89 m2/g. The reduction profiles revealed the presence of different Co and Mo species and the existence of metal-support interactions. The use of cobalt chloride formed particles of large sizes and Cl− blocks the active sites. The reduced catalysts showed greater activity than the unreduced catalysts at 400 °C. The most active catalysts were the one that contained 4 wt.% of Mo (in the monometallic) and that with the higher Mo content (in the bimetallic).