Desarrollo de la cromatografía de líquidos a alta temperatura y de microondas para el análisis de alimentos

Resumen

Currently, in the analytical laboratories, there are plenty of analyses that require a separation prior to the determination of the analytes. The chromatographic techniques have appeared as the best approaches for carrying out this separation. Among all of the chromatographic techniques, liquid chromatography is compatible with virtually all of the analytes. For this reason, it is considered to be the most versatile chromatographic modality and, therefore, it has experienced a great development in the last few decades. The determination of carbohydrates, carboxylic acids and alcohols in food samples is essential since these compounds affect their sensory and nutritional quality. On the other hand, the content in some elements including heavy metals gives an assessment about the potential toxicological risk of food. The food industry requires from fast and accurate analysis techniques. In this Doctoral Thesis new tools for the study of the chemical composition of food have been developed and evaluated. The chosen analytes have been carbohydrates, alcohols, metals and arsenosugars. The study has been focused on the evaluation of several stationary phase heating modes. Thus, the use of a conventional gas chromatography (GC) oven allows working at temperatures higher than those reached by conventional HPLC ovens. In this case, the separation is carried out according to the so called High Temperature Liquid Chromatography (HTLC). Besides, a microwave oven has also been used thus giving rise to a new chromatographic technique: MicroWave High Performance Liquid Chromatography (MW-HPLC). The coupling of these chromatographic systems to several detectors such as ICP-AES, ICP-MS, ELSD, RI, and UV are presented as innovative tools for the food analysis. In a more detailed way, the objectives have been the following: a. Study of the resolution and efficiency improvement by HTLC over HPLC. b. Characterization of the HTLC system coupled to conventional detectors such as RI and ELSD, testing the effect of various parameters such as temperature on the separation efficiency. In addition, the possibility of working under temperature gradient conditions has been evaluated. c. Optimization of the system to adapt the HTLC technique to an inductively coupled plasma - atomic emission spectrometer, ICP-AES, and comparison of the analytical figures of merit with those obtained using HTLC-ELSD and HTLC-RI. d. Use of the HTLC-ICP-AES association for the simultaneous determination of organic compounds and metals. Indeed, this methodology has been applied to the determination of organic compounds such as sugars, alcohols and metals in foodstuff samples (milk, ice cream, fruit juices, alcoholic beverages¿). e. Study of the HTLC-ICP-MS coupling for the arsenic speciation and the application to real biological samples. f. Assessment of the use of microwave radiation in HPLC (MW-HPLC) as an alternative to the conventional oven heating. The above-mentioned objectives are innovative because this is the first time that HTLC has been adapted to an ICP-AES system to carry out the determination of organic compounds and metals in a single chromatographic run. In addition, the hyphenations HTLC-ELSD and HTLC-ICP-MS are also innovative to determine some of these species. Such associations show major advantages in terms of simplicity of the interface (it might be sufficient to adapt the exit of the column directly to either the spray chamber of the ICP system or the dispersive detector. Finally, it is also the first time that the MW radiation has been used to improve the efficiency of a separation by HPLC.