Identifier: TDX:797
Authors: Gómez Cortés, Verónica
Abstract:
Environmental analysis is a field with high interest in the analytical chemistry community. It is very important to assure and maintain the quality, from air as well as from water, to avoid that its composition cause any risk for the living organisms. Different industrial processes have contributed to improve health quality, but they can produce intermediates that if are introduced direct or indirectly to the waters can cause important problems of pollution. In that way, it is necessary to treat a big amount of industrial wastes, which should be continuously minimized. <br/> <br/>Advances in the environmental field have been focusing on the development of new techniques of easy use, with low sample manipulation, low costs and short analysis times that could be easily automatised and fast. Flow analysis techniques can be found in this classification.<br/><br/> The current analytical instruments can generate data with different dimensionality. The analytical signal can be a scalar (a single absorbance measure), a vector (single absorbance measurement along time), or a data matrix (spectrum recorded along time) per each analysed sample. These data have been classified, as zero-order data when the signal is a scalar, first-order data when is a vector, and second-order data when the signal is a matrix. Zero-order data are useful for cases in which we have a unique and specific response for the analyte of interest, meanwhile first-order data allow quantification of an analyte in the presence of interferents but they should be contained in the calibration samples. When the interferents are not known and they could not be present in the calibration samples, second-order data and second-order calibrations are used.<br/><br/>This doctoral thesis has been carried out for developing new analytical methodologies for determining subproducts of the tanning industry using sequential injection analysis (SIA) and second-order calibration.<br/><br/>SIA, Sequential Injection Analysis, is a flow injection system introduced in 1990 by Professor Jaromir Ruzicka, where the sample and reagents are introduced sequentially into the system, are mixed by diffusion process in the reactor and then they are pumped through the detector.<br/>A SIA system using a diode array spectrophotometer can generate second-order data, it means that the analytical signal is a data matrix for each sample on which we have absorbances in a wavelength interval in one axis and in a time interval in the other axis.<br/><br/> In this project, we present different practical applications using sequential injection analysis and second-order calibration using multivariate curve resolution alternating least squares (MCR-ALS) for determining and speciating chromium and for determining three acid dyes simultaneously. Furthermore we present two bibliographic overviews about chromium determination and multicomponent analysis in flow systems. We also developed an application of sequential injection chromatography (SIC) using multivariate curve resolution alternating least squares (MCR-ALS) for determining phenolic derivatives.<br/><br/> Chromium is an element widely used in the industry. Its determination presents high environmental interest because the toxicity of the Cr(VI) species as a carcinogenic agent, meanwhile Cr(III) is an essential element. In this Thesis we present four papers relative to chromium determination. The first paper Use of multivariate curve resolution for determination of chromium in tanning samples using sequential injection analysis, Analytical and Bioanalytical Chemistry 382 (2005) 328-334 is based on the basis to permit quantification of chromium with the system SIA-MCR-ALS. Depending on the capacity of reaction of Cr(III), different analytical sequences in the SIA system can be designed. Cr(III) was oxidized into Cr(VI) outside of the SIA system to increase Cr(III) sensibility. In that way, in the SIA system we induced a pH gradient to see the conversion of the two species of Cr(VI), chromate and dichromate. The second paper Factorial design for optimizing chromium determination in tanning wastewater, Microchemical Journal 83 (2006) 98-104 presents an automatic system for total chromium determination using different experimental designs to optimize the overall process. The third paper, Chromium speciation using sequential injection analysis and multivariate curve resolution, Analytica Chimica Acta 571 (2006) 129-135 is a paper in which the two main species of chromium, Cr(III) and Cr(VI), are determined simultaneously in a single analysis in the presence of interferents. The fourth paper, Chromium determinations and speciation since 2000, Trends in Analytical Chemistry, 25 (2006) 1006-1015 is a bibliographic study that describes the possibilities available for chromium determination and speciation.<br/><br/>Other analytes of interest in this field are dyes from wastewater due to its high toxicity and its low biodegradability. That is why studying the proportion of dyes in samples and its effect through time presents high relevance. Chromium and dyes are compounds of high interest in other application fields, such as, foods, printing and graphic design, etc. We present four scientific papers in this field with two practical objectives. On the one hand, control the amount of dyes that remains in solution after the dyeing process has been done. On the other hand, study different strategies to reduce the percentage of dyes in wastewater. The first paper, Sequential injection analysis with second-order treatment for the determination of dyes in the exhaustion process of tanning effluents Talanta 71 (2007) 1393-1398, describes the developed method for determining three acid dyes in a single step. This method was applied to water samples of leathers tanned with chromium salts and with vegetal agents. The second paper Matrix effect in second-order data. Determination of dyes in a tanning process using vegetable tanning agents Analytica Chimica Acta 600 (2007) 233-239 presents strategies to use when a sample presents matrix effects using second-order data. To solve the second objective, we studied the behaviour of dyes on activated carbon and present the results in the third paper Kinetic and adsorption study of acid dye removal using activated carbon Chemosphere 69 (2007) 1151-1158 where we studied the adsorption and the kinetic parameters of dyes being alone in solution or in a mixture of them. The fourth paper, Experimental designs for optimizing and fitting the adsorption of dyes onto activated carbon Submitted, we described a sequential methodology to obtain a response surface and optimize the adsorption process as a way of eliminating dyes in wastewater samples from the tanning industry. <br/><br/>In the last period of the Thesis, we explored different strategies to increase the capacity of simultaneous analysis using flow systems and second-order calibration. From this study, we obtained two papers. The first, Multicomponent analysis in flow systems, Trends in Analytical Chemistry, 26 (2007) 767-774, shows a general vision of multiple determinations in flow systems. The second paper, Coupling of sequential injection chromatography with multivariate curve resolution alternating least squares for enhancement of peak capacity, Analytical Chemistry 79 (2007) 7767-7774 shows a combination of two strategies proposed for multicomponent analysis, sequential injection chromatography (SIC) and second-order calibration with MCR-ALS. This study was carried out in collaboration with the Analytical Chemistry, Automation and Environment group of the University of the Balearic Islands.
Repositori URV