Nuevos retos de la microextracción en fase líquida acoplada a cromatografía líquida para determinación de compuestos orgánicos

Laburpena

One of the more difficult stages in the development of an analytical method is the sample preparation. For this reason, an important part of the Analytical Chemistry research is focused towards the simplification of this step. In this sense, miniaturization and automation are key trends in the improvement of different practical aspects of the suitability of analytes for their instrumental measurement. Microextraction techniques can be divided into two large groups, those that isolate analytes into a solid phase, solid-phase microextraction (SPME), and those that extract them into a liquid phase, liquid-phase microextraction (LPME). Research in this PhD Thesis has focused on the development of procedures based on LPME, specifically dispersive liquid-liquid microextraction (DLLME), liquid-liquid microextraction (LLME) and cloud point extraction (CPE). Chromatographic techniques are very suitable for the analysis of extracts obtained through miniaturized sample treatment techniques, since they allow the separation of compounds with very similar molecular structures, which could not be differentiated in any other way. In this Doctoral Thesis, all the analytical methods developed involve liquid chromatographic (LC) separations, as they are the best option for the organic compounds studied. On the other hand, fluorimetric detection (FLD) and mass spectrometry (MS) have been the techniques selected for the monitoring of compounds separated by LC, taking into account the high sensitivity and selectivity provided by these detection systems. In this Thesis, MS in tandem (MS/MS) has been used, by means of the use of a triple quadrupole (QqQ) as mass analyzer, which has allowed the identification of the analytes without possibility of doubt, thanks to the characteristic fragmentation patterns under the selected conditions. Research presented focuses on the analysis of samples of very different nature involving problems that in one way or another concern society, since it deals with the detection of compounds of interest in the food and pharmaceutical industries, contaminants in different environmental compartments and biomarkers in biological fluids. Thus, plants, water and soil from different sources, as well as human urine have been the matrices under analysis. The compounds determined have been three forms of vitamin K (phylloquinone, menaquinone and menadione), herbicides (glyphosate, glufosinate and aminomethylphosphonic acid (AMPA)), inhibitors of the enzyme phosphodiesterase-5 (sildenafil, tadalafil, vardenafil and N-desmethylsildenafil) and biomarkers (glyoxal and methylglyoxal). The presentation of the developed work has been structured in five chapters: Chapter I. Determination of the glyoxal and methylglyoxal biomarkers, previously derivatized by reaction with 2,3-diaminonaphthalene to form the corresponding ?- quinoxalines, which are preconcentrated in 1-undecanol by DLLME assisted by the surfactant Triton X-114. The analysis of the extracts obtained from urine is carried out by LC-FLD. Chapter II. Determination of four phosphodiesterase-5 inhibitors in waters and human urines. The analytes are preconcentrated by DLLME and the enriched extract is analysed by LC-ESI-QqQ-MS/MS. Chapter III. Microwave-assisted CPE application, using Triton X-114, for the preconcentration of three forms of vitamin K, previously extracted from plant samples by ultrasound assisted extraction. The LC-ESI-QqQ-MS/MS combination was used for instrumental measurement. Chapter IV. Determination of glyphosate and its metabolite AMPA in waters and plants using LC-FLD. The herbicides were derivatized with 9-fluorenylmethyl chloroformate and pre-concentrated in methyl isobutyl ketone in the form of ionic pairs by means of LLME. Chapter V. Determination of glyphosate, glufosinate and AMPA in waters, plants and soils, applying the derivatization and preconcentration methodology developed in chapter IV and carrying out the analysis by LC-ESI-QqQ-MS/MS. The five methods of analysis presented have been validated following the International Guidelines for the validation of analytical methods.