## 6 Prospects and Trends  
Recent trends in sample preparation techniques comprise miniaturization, automation, high-throughput performance, on-line coupling with analytical instruments as well as low-cost operation through extremely low or no solvent consumption. Among other techniques mentioned in this review, SPME has the potential to meet these challenges [50]. Through miniaturization of sample preparation steps time and operation costs can be saved. The main advantage however is the possibility to determine trace and ultratrace analytes in complex matrices. In addition to SPME techniques, further selective extraction procedures have been developed. They all show clear trends toward simplification of sampling and sample preparation methods, an increase in reliability and precision, and the elimination of the cleanup step. The development of more sensitive and selective phases may be a step towards further miniaturization of these techniques. Increasing interest also lies in the field of automating sample preparation. Automation can result in faster procedures as well as improved precision and cost-effectiveness. Over the last decade, sample preparation devices have been automated and coupled to separation and detection systems specifically designed for automation. Due to the lack of automation, SPME tends to be coupled more often to GC than to LC. Moreover, more recent techniques such as SBSE are not yet as widely accepted as SPME due to the difficulty ofachieving full automation. Another challenge related to new SPME techniques that has to be overcome is the carry-over effect occurring for example in SPDE, in-tip SPME and MEPS techniques due to the remaining of analytes on the inner surface of the needle after heat desorption [50, 63, 64, 387]. Another aspect that should be considered for optimization is the moderate enrichment capacity of these techniques [50]. Research regarding SPME is not only based on the development of new devices but also on the study of derivatization strategies, new coatings with higher extraction efficiencies, selectivity and stability, and the study of novel calibration processes [2]. During the SPME process there are many different parameters that can be applied to achieve specific methods. Derivatization for example is a valuable tool in many cases to achieve efficient extraction. With regard to chemical consumption and waste generation, a recent trend however is to avoid derivatization techniques where possible [98]. The variety of commercially available fiber coatings is constantly growing which open up the range for further applications. However, in addition to these commercially available sorbents, further promising coating procedures have been developed. This approach opens up new fields of application. Furthermore, efforts are made to overcome limitations in biocompatibility, on-site compatibility, selectivity and sensitivity of currently available SPME coatings [103, 104]. Besides physical coating processes which are compatible with nearly all kinds of sorbent materials there is a clear trend towards procedures developed for specific components. Most attention in past years has been given to the application of nanomaterials [115, 370]. Nanostructured MIP-based coatings will continue to be of particular interest. Great attention is currently given to such specific SPME coatings as a basis for development of more designable structures. Even when issues like selectivity for target analytes and applicability for samples with complex matrix compositions have to be solved [24]. Quantitation is currently the major challenge for SPME procedures to gain wider application. This review showed that calibration techniques are still under development [22]. The model calculation methods laid down in chapter 2.5 provide a meaningful approach to overcome these challenges. A better understanding of SPME processes will be the basis of further improvements. Nonetheless, a number of norms have already been implemented and indicate that the application of calibration methods in SPME is possible.