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Background: Saliva samples collected from one 58 year old male and one 35 year old female during 7 days of fasting were analyzed by direct immersion of both C18 and mixed-mode biocompatible solid-phase microextraction fibers, in combination with a LC–MS method using a benchtop orbitrap instrument in both positive and negative ionization modes, in order to evaluate the difference in terms of metabolite coverage. Results: The mixed-mode coating provided better results, with the simultaneous extraction of a higher number of both hydrophilic and hydrophobic metabolites. The ability of detected features to distinguish differences between the individuals and changes in saliva metabolome induced by diet was also demonstrated. Conclusion: Saliva may be useful for medical diagnostics as it is non-invasive. The use of biocompatible solid-phase microextraction fibers can play an important role as an alternative sample preparation method for untargeted LC–MS metabolomics studies on human saliva because it provides simultaneous extraction of metabolites with a wide range of polarity, thus allowing the detection of changes in metabolic pathways with unsupervised statistical analyses.

Conventional in vitro or ex vivo bioanalytical quantitative sample preparation methods for the determination of compounds in biological tissues are often coupled with challenges in obtaining an assay representative of the system of interest. The rising interest in in vivo microsampling bioanalytical methods is due to the unique advantages they offer over their in vitro counterparts. In vivo solid-phase microextraction (SPME), a diffusion-based microsampling tool, has been successfully applied in recent studies to various biological systems. This review presents recent trends in tissue bioanalysis using in vivo SPME as a sample preparation tool. Efforts were made to discuss the various bioapplications of the method while highlighting possible strategies for improved sensitivity where needed. In vivo SPME devices currently employed for the various applications have also been described. In addition, we highlight selectivity of a new class of biocompatible coatings that can potentially improve the coverage of metabolites for untargeted metabolomics.

Background: A high-throughput bioanalytical method using 96-blade thin film microextraction (TFME) and LC–MS/MS for the analysis of repaglinide (RPG) and two of its main metabolites was developed and used for an in vitro metabolism study. Results: The target analytes were extracted from human microsomal medium by a 96-blade-TFME system employing the low-cost prototype ‘SPME multi-sampler’ using C18 coating. Method validation showed recoveries around 90% for all analytes and was linear over the concentration range of 2–1000 ng ml-1 for RPG and of 2–500 ng ml-1 for each RPG metabolite. Conclusion: The method was applied to an in vitro metabolism study of RPG employing human liver microsomes and proved to be very useful for this purpose.

Solid phase microextraction (SPME) is well-established technology in bioanalysis. Current review discusses the features of SPME, which determine the non- or low-invasiveness of the method in biomedical analysis. In the first section we analyze the factors, which have significant influence on the SPME sampling device performance in the view of sampling safety and efficiency. In the later sections applicability of various SPME approaches for analysis of easily accessible samples routinely used for analysis (e.g., urine, blood) as well as limited availability samples (tissues) is discussed. Moreover, the examples of sampling alternative matrices such as hair, saliva, sweat or breath are presented. The advantages and limitation of the technology in the view of future development of SPME are also reviewed.