In recent years one of the most important trends in Analytical Chemistry has been the development of new analytical methodologies based on the miniaturization, simplification and automatization of the analytical process, in order to reduce the environmental impact of the analysis without compromising the sensitivity and selectivity. In this respect miniaturized liquid chromatography (LC) systems, such as capillary liquid chromatography (CapLC) and nanoliquid chromatography (NanoLC) are important achievements. These techniques are environmental friendly because the amount of material involved is limited and organic solvents, electricity and the wastes generated are lower than in conventional scale LC. In addition, CapLC and NanoLC provide an improvement of the sensitivity and even selectivity with respect to conventional LC. On the other hand, sample treatment is one of the most important steps of analytical process; as it is usually necessary to eliminate most endogenous compounds and to concentrate analytes, which are often present at low concentrations in the sample. Sample treatment is typically the most time-consuming step of the analytical process. This is because conventional off-line sample preparation techniques generally require laborious procedures that are susceptible to produce analyte loss and contamination. In addition, most of them are difficult to automatize. Therefore, these methodologies are gradually being replaced by solid-phase microextraction (SPME), a green approach to sample preparation which minimizes solvent consumption and generation of wastes. SPME is also less time consuming and more cost effective than traditional procedures. In-tube solid-phase microextraction (IT-SPME) is an interesting alternative to other SPME techniques, because it combines miniaturization, automation and reduction of solvent consumption, and it can be also coupled to LC systems. The limited number of extraction columns available is the most important limitation of IT-SPME, paticularly coupled to CapLC and NanoLC. Therefore, it is necessary to develop new sorbents for IT-SPME. The research carried out in the course of the present thesis has been mainly focused on the development of new strategies for the implementation of IT-SPME through new configurations of coupling and the synthesis of new extractive phases or the reutilization of waste (ashes). More specifically, the research has been intended to facilitate the on-line coupling of IT-SPME to miniaturized LC equipments, as well as to develop in situ non-invasive strategies for the analysis of different pollutants and wastes. Special attention has been developed to polar compounds because of their high mobility in the environment. In some cases, the studies have been extended to their degradation products. Therefore, this thesis is intended to improve knowledge about IT-SPME, exploring new materials as extractive phases, as well as to consolidate the coupling with miniaturized LC, especially NanoLC and others techniques amenable for in situ or non-invasive studies, and from a perspective of the Green Analytical Chemistry principles.