## 1 Introduction  
High extraction efficiencies, although always desirable, are essential in techniques that integrate on-line sample preparation and LC. This is the case of IT-SPME. In this modality of microextraction, the extractive phase is typically the coating of a capillary column used in replacement of the injection valve inert loop, so that the extraction takes place simultaneously with the sample loading. A subsequent change in the valve position allows the desorption and transfer of the retained analytes to the separative column by means of the mobile-phase. Today, IT-SPME is a well-established technique that has been successfully used in many fields of applications [1; 2; 3]. This technique is especially well-suited for miniaturized LC systems such as Capillary-LC (Cap-LC) and Nano-LC. This is because relatively large sample volumes can be loaded into the extractive capillary for on-line analyte enrichment overcomingthe lack of sensitivity derived from the fact that only low volumes of the samples can be injected in miniaturized LC systems. The utility of IT-SPME in Cap-LC has been demonstrated through a wide variety of applications mainly in the environmental and biomedical fields [4; 5; 6; 7] and, very recently, IT-SPME has been coupled to Nano-LC [8; 9]. Substantial progress in the area can be expected through the development of new sorbents for the improved extraction of a wide variety of analytes and matrices. In recent years, several materials have been used as sorbents for extraction and microextraction of organic compounds. Successful examples have been reported using a variety of polymers, ionic liquids, metal organic frameworks, covalent organic frameworks and different types of NPs such as carbon, metal or metal oxide NPs [10; 11]. Among them, nanostructured sorbents have gained significant interest due to their inherent advantages, especially their high specific surface for interaction with the target compounds and the possibility of increasing the affinity for the analytes through a variety of interactions [12; 13]. As regards solid-phase microextraction, most of the efforts made have been focused on the development of coatings for fibres [14], whereas only a few sorbents with nanomaterials for IT-SPME have been reported so far. Examples are the employment of titanium [15] or silica [16] capillaries chemically treated to produce nanostructured internal surfaces. From a different perspective, a polymeric phase can be reinforced with NPs. For example, in previous studies, we demonstrated that the functionalization of commercial polydimethylsiloxane (PDMS) coated columns with different types of carbon nanotubes (CNTs) may improve the extraction efficiency for a variety of compounds such as drugs and pollutants [5; 6]. More recently, polymeric coatings of tetraethyl orthosilicate (TEOS) and trimethoxyethylsilane (MTEOS) were functionalized with SiO\({}_{2}\) NPs and used for the extraction of herbicides of different polarities. The presence of SiO\({}_{2}\) NPs increased the extraction efficiency for most of the compounds tested [7]. As a continuation of those studies, in the present work we have synthetized a TEOS-MTEOS polymer modified with TiO\({}_{2}\) NPs. This type of NPs has been extensively investigated in SPME with fibres and other forms of microextraction [17]. However, their application to IT-SPME is still very limited [15]. The new TEOS-MTEOS/TiO\({}_{2}\) NPs composite has been tested for the IT-SPME of variety of organic pollutants, and the results have been compared with those obtained with the polymer modified with SiO\({}_{2}\) NPs, as well as with different commercially available capillaries coated with polymers. The commercial capillaries tested were TRB 35, FFAP and PS-DVB, with coatings of 35% polydiphenyl-65% polydimethyl siloxane (PDMS), nitroterephthalatic acid modified poly (ethyleneglycol) (PEG) and polystyrene-divinylbenzene (PS-DBV), respectively. The proposed phases were tested for different types of substances.