Detectores espectroelectroquímicos en flujoaplicaciones analíticas al estudio de medios contaminados

Resumo

Today's society constantly demands the development of new analytical methods, more accurate, sensitive and reliable in an attempt to control the quality of food, drugs, water and the air we breathe, the productive processes and waste generated by our civilized way of life. In addition, it is required that these methods are easy to implement, it only suffices to press a button to get the result, so that a technician with basic training is able to process the necessary samples. A factor that has led to progress significantly in this direction has been the automation of the measures through the use of computers and microprocessors, which prevent the investigator the most tedious tasks of calculation and experiment care, among others, and frees him for more creative work, which requires his presence without appeal. Types of analytical techniques that can be easily automated are flow techniques, among which, chromatographic methods and flow injection analysis (FIA) techniques stand out. Both require sensing devices that detect the presence of chemical species of interest by measuring a characteristic property while circulating through the system. The measured property should be, if possible, a distinctive feature of the analyte with respect to the other species present in the sample, to avoid interference, and also it must be proportional to its concentration to allow quantification. The spectro-electrochemistry is a hybrid technique that combines two classic methods, electrochemistry and spectroscopy for chemical information. An essential feature of this technique is that both measures are obtained simultaneously and not sequentially, as with other hybrid techniques. Thus, non-stationary processes occurring near the electrode can be easily studied. Analytical advantages are also obtained, since by measuring two properties simultaneously, interference is more difficult to happen. Despite the widespread use of spectro-electrochemistry in many laboratories, it doesn't have much commercial instrumentation yet. Therefore, the combination of electrochemical and spectroscopic apparatus is made, differently, in each laboratory. The spectro-electrochemical cell is the interface between techniques, although it has been described how to build them, but, until now, there is no standard model used by most of the scientific community. This thesis describes how to design and manufacture a simple spectro-electrochemical flow cell, easy to build and with highly configurational versatility. It has been proven the possibility of using it as a spectro-electrochemical detector for determining electro-generated potassium ferricyanide by injection of potassium ferrocyanide samples at a flow system. Furthermore, it has been shown that this type of mixed sensors provides higher sensitivity levels that when two detectors sequentially-arranged are used. To demonstrate the applicability of this sensor in environmental-related studies, two analytical methods have been developed, one for speciation of inorganic soluble copper in water samples and one for determination of imazapyr herbicide in aqueous solutions. The proposed speciation method of Cu(I) and Cu(II) shows how the use of a mixed detector independently quantifies both copper oxidation states through two different techniques: spectrophotometric determination of Cu(II) with cuprizone, and amperometric detection of Cu(I). Both measures are synchronized to prevent interference between them. Moreover, a spectro-electrochemical flow method is also proposed for the determination of imazapyr by spectrophotometry in the UV wavelength. The sensitivity of this method is greatly enhanced by the electrochemical polarization of the working electrode present in the flow-cell, reaching adequate levels of detection for maximum tolerance levels set by EPA and FDA, without previous extraction and/or preconcentration stages.