O Proceso analítico

Titulación: Grao en Química -- Materia: Química Analítica IEsta unidade didáctica enfócase de maneira que permita proporcionar unha visión global da Química Analítica e a súa terminoloxía básica, mostrando a importancia da Química Analítica para a resolución de problemas de diversos ámbitos. Este enfoque faise sobre o esquema do proceso analítico como medio de resolución dunha determinada problemática analítica real. Deste xeito, partindo dun esquema sinxelo, explícase o obxectivo e as distintas etapas do proceso analítico: definición do problema a resolver, selección do método máis adecuado e as operacións derivadas desta selección, toma e tratamento da mostra, medida do (ou dos) analito(s), tratamento e interpretación dos resultados experimentais obtidos, e finalízase a súa explicación coa toma de decisións. Durante a formulación e desenvolvemento do tema déixase claro que a simple determinación da composición dunha mostra non é o obxectivo principal da Química Analítica, senón que o obxectivo desta disciplina é a obtención de información útil de calidade para resolver o problema exposto que foi o que propiciou o inicio do proceso analítico. Ademais, neste tema resáltase que o método seleccionado para realizar unha determinación analítica debe depender do tipo de información que se necesita obter, e que non sempre compensa elixir a metodoloxía máis complicada ou a máis custosa.Universidade de Santiago de Compostela. Servizo de Normalización Lingüístic

Tratamento dos datos analíticos

Titulación: Licenciatura en Química -- Materia: Química Analítica IIEsta unidade didáctica é a primeira toma de contacto do alumnado co estudo do tratamento dos datos analíticos e a comprobación da súa calidade. Este estudo poderase completar máis adiante dentro do programa desta materia cando se presente o resto dos parámetros de calidade dos métodos analíticos. A importancia deste tema radica en que unha vez obtidos os datos analíticos, o primeiro aspecto que se ten que considerar é a verificación da calidade dos mesmos en termos de exactitude e precisión. A presenza ineludible de erros aleatorios impón o concepto de variabilidade dos datos, e obriga ó tratamento estatístico dos resultados co fin de estimar a fiabilidade e a robustez do método analítico. Ademais, a análise non se pode considerar finalizada ata que os datos obtidos non sexan procesados e expresados de maneira que poidan extraer toda a información que se require para a resolución do problema analítico. Como a unidade didáctica anterior está dedicada a proporcionar unha visión global da Química Analítica centrada sobre o esquema do proceso analítico,a orde lóxica das seguintes unidades didácticas debería basearse na disposición cronolóxica das súas distintas etapas. Porén, esta unidade, que en realidade debería ser impartida ao final do programa, por ser o tratamento de datos unha das últimas etapas do proceso analítico, sitúase ao principio. A ruptura desta orde lóxica débese a un criterio práctico compartido pola xeneralidade dos docentes que imparten esta materia na nosa universidade e noutras, tanto españolas coma estranxeiras. Por exemplo, non é doado explicar a varianza asociada ó proceso de mostraxe (unidade didáctica III) se previamente non se introduce o concepto de erro, os tipos de erros e os parámetros estatísticos que se poden utilizar para avalialos. Do mesmo xeito, cando se define límite de detección e de cuantificación dun método analítico (unidade didáctica IV) será necesario explicar previamente os erros asociados á incerteza dunha determinación analítica.Universidade de Santiago de Compostela. Servizo de Normalización Lingüístic

Determination of Volatile Compounds in Four Commercial Samples of Japanese Green Algae Using Solid Phase Microextraction Gas Chromatography Mass Spectrometry

Green algae are of great economic importance. Seaweed is consumed fresh or as seasoning in Japan. The commercial value is determined by quality, color, and flavor and is also strongly influenced by the production area. Our research, based on solid phase microextraction gas chromatography mass spectrometry (SPME-GC-MS), has revealed that volatile compounds differ intensely in the four varieties of commercial green algae. Accordingly, 41 major volatile compounds were identified. Heptadecene was the most abundant compound from Okayama (Ulva prolifera), Tokushima (Ulva prolifera), and Ehime prefecture (Ulva linza). Apocarotenoids, such as ionones, and their derivatives were prominent volatiles in algae from Okayama (Ulva prolifera) and Tokushima prefecture (Ulva prolifera). Volatile, short chained apocarotenoids are among the most potent flavor components and contribute to the flavor of fresh, processed algae, and algae-based products. Benzaldehyde was predominant in seaweed from Shizuoka prefecture (Monostroma nitidum). Multivariant statistical analysis (PCA) enabled simple discrimination of the samples based on their volatile profiles. This work shows the potential of SPME-GC-MS coupled with multivariant analysis to discriminate between samples of different geographical and botanical origins and form the basis for development of authentication methods of green algae products, including seasonings

Sintesis y aplicacion de dos resinas quelatantes: PAMF y PDTC para la preconcentracion de metales en aguas naturales Determinacion por EAA con llama

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Indirect fibre-optic colorimetric determination of ascorbic acid using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and cloud point extraction

A new method has been developed for the indirect determination of ascorbic acid (AA) in commercial syrup preparations based on cloud point extraction (CPE) separation and preconcentration, and determination by molecular absorption spectrometry. The colorimetric method was based on the reduction of Fe(III) to Fe(II) and complexation of Fe(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP), followed by its extraction into Triton X-114. Selectivity of the method was increased with the use of EDTA as a masking agent. The absorbance was measured at 742 nm. Various influencing factors on the separation and preconcentration of AA have been investigated systematically, and the optimized operation conditions were established. The proposed method allows the determination of AA in the range 5200 mu g L1 with a relative standard deviation of 3.0%. The detection limit was found to be 0.9 mu g L1 for AA. This method has been applied to the determination of ascorbic acid in commercial pharmaceutical preparations. Copyright (c) 2011 John Wiley & Sons, Ltd

The cientificWorldJOURNAL Research Article Stabilizing Agents for Calibration in the Determination of Mercury Using Solid Sampling Electrothermal Atomic Absorption Spectrometry

Tetramethylene dithiocarbamate (TMDTC), diethyldithiocarbamate (DEDTC), and thiourea were investigated as stabilizing agents for calibration purposes in the determination of mercury using solid sampling electrothermal atomic absorption spectrometry (SS-ETAAS). These agents were used for complexation of mercury in calibration solutions and its thermal stabilization in a solid sampling platform. The calibration solutions had the form of methyl isobutyl ketone (MIBK) extracts or MIBK-methanol solutions with the TMDTC and DEDTC chelates and aqueous solutions with thiourea complexes. The best results were obtained for MIBK-methanol solutions in the presence of 2.5 g L −1 TMDTC. The surface of graphite platforms for solid sampling was modified with palladium or rhenium by using electrodeposition from a drop of solutions. The Re modifier is preferable due to a higher lifetime of platform coating. A new SS-ETAAS procedure using the direct sampling of solid samples into a platform with an Re modified graphite surface and the calibration against MIBK-methanol solutions in the presence of TMDTC is proposed for the determination of mercury content in solid environmental samples, such as soil and plants

Routine Analyses of Trace Elements in Geological Samples using Flow Injection and Low Pressure On-Line Liquid Chromatography Coupled to ICP-MS: A Study of Geochemical Reference Materials BR, DR-N, UB-N, AN-G and GH

International audienceWe describe analytical procedures for trace element determinations developed at the CNRS Service d'Analyse des Roches et des Minéraux (SARM) and report results obtained for five geochemical reference materials: basalt BR, diorite DR‐N, serpentinite UB‐N, anorthosite AN‐G and granite GH. Results for rare earth elements, U and Th are also reported for other reference materials including dunite DTS‐1, peridotite PCC‐1 and basalt BIR‐1. All rocks were decomposed using alkali fusion. Analyses were done by flow injection ICP‐MS and by on‐line low pressure liquid chromatography (LC)‐ICP‐MS for samples containing very low REE, U and Th concentrations. This latter method yielded limits of determination much lower than data by direct introduction and eliminated possible isobaric interference on these elements. Although results agree with most of the working values, when available, results for some elements differed slightly from the recommended concentrations. In these cases, we propose new values for Co, Y and Zn in basalt BR, Zr in diorite DR‐N, Sr and U in granite GH, and Ga and Y in anorthosite AN‐G. Furthermore, although the Sb concentration measured in AN‐G was very close to our limit of determination, our value (0.3 ± 0.1 μg g−1) is much lower than the reported working value of 1.4 ± 0.2 μg g−1. These new values would need to be confirmed by a new inter‐laboratory programme to further characterise these reference materials.Results obtained for REE, Th and U concentrations using the on‐line low pressure LC‐ICP‐MS yielded good limits of determination (ng g−1to sub‐ng g−1for rocks and ng l−1to sub‐ng l−1for natural waters) and accurate results. The efficiency of the matrix separation allowed accurate measurements of Eu without the need to correct the BaO isobaric interference for samples having Ba/Eu ratios as high as 27700. For REE concentrations in PCC‐1 and DTS‐1, differences with values reported in the literature are interpreted as resulting from possible heterogeneity of the reference materials. Thorium and U values are proposed for these two samples, as well as for AN‐G and UB‐