Overview of extraction methods for analysis of vitamin D and its metabolites in biological samples.

In the last decade the scientific and medical community was confronted with a renewed interest in vitamin D and its metabolites, interest prompted by new discoveries regarding the association between members of the vitamin D family and a great number of physiological functions and pathological states. An impressive number of research projects have helped clear the path towards a better understanding of the functions of vitamin D and have resulted in the development of numerous methods of analysis. This review focuses on the various extraction methods used for analysis of vitamin D in research or clinical settings. Two main extractive methods are usually employed: liquid-liquid extraction and solid-phase extraction. Some methods use no extraction step and direct analysis is performed at the cost of significantly increased matrix interference. On the other hand, other methods use combined extraction techniques, and even additional derivatization steps in order to increase the sensitivity and accuracy of the analysis. The method of choice ultimately depends on the research question and the purpose of the study.

Analytical methods used in conjunction with solid-phase microextraction: a review of recent bioanalytical applications.

Integration of sampling and sample preparation with various analytical instruments is a highly desirable feature for any analytical method. This is most conveniently achieved by using microextraction techniques or various microdevices. Among these techniques, solid-phase microextraction (SPME) is particularly remarkable due to its simplicity and effectiveness. This review discusses the most recent applications of SPME in bioanalysis, grouped according to the analytical instrument that SPME is coupled to. It is shown that one of the most important aspects of such analytical methods is the ability of SPME to perform direct and selective extraction of analytes from complex biological samples. By far, the most popular method continues to be SPME coupled to GC. Nevertheless, the last 2 years have witnessed significant advances in other areas, such as successful automation of SPME coupled to liquid chromatography and the development of new coatings suitable for direct extraction from biological samples. Furthermore, a few bioanalytical applications based on direct coupling of SPME to MS, ion mobility spectrometry, CE and analytical chemiluminescence have been reported.

Biocompatible solid-phase microextraction coatings based on polyacrylonitrile and solid-phase extraction phases.

The applications of solid-phase microextraction (SPME) are continuously expanding, and one of the most interesting current aspects consists of applying SPME for fast analysis of biological fluids. The goal of this study is to develop biocompatible SPME coatings that can be utilized for in vivo and in vitro extractions, in direct contact with a biological matrix such as blood or tissue. The biocompatibility of the proposed new coatings is confirmed by X-ray photoelectron spectroscopy, and their performance is tested by developing an SPME/HPLC method for analysis of verapamil, loperamide, diazepam, nordiazepam, and warfarin in buffer solutions and in human plasma. The coatings prove to be biocompatible by not adsorbing proteins and are successfully applied for fast drug analysis and assay of drug plasma protein binding.

Fast in vivo microextraction: a new tool for clinical analysis.

BACKGROUND: We sought to develop a technique with the potential to partly replace current methods of analysis based on blood draws. To achieve this goal, we developed an in vivo microextraction technique that is faster than conventional methods, interferes minimally with the investigated system, minimizes errors associated with sample preparation, and limits exposure to hazardous biological samples. METHODS: Solid-phase microextraction devices based on hydrophilic polypyrrole and polyethylene glycol coatings were used for direct extraction of drugs from the flowing blood of beagle dogs, over a period of 8 h. The drugs extracted on the probes were subsequently quantified by liquid chromatography coupled to tandem mass spectrometry. Two calibration strategies--external and standard on the fiber--were used to correlate the amount extracted with the in vivo concentration. RESULTS: Diazepam and its metabolites were successfully monitored over the course of a pharmacokinetic study, repeated 3 times on 3 beagles. The fast microextraction technique was validated by comparison with conventional plasma analysis, and a correlation factor of 0.99 was obtained. In addition to total concentrations, the method was useful for determining free drug concentrations. CONCLUSIONS: The proposed technique has several advantages and is suitable for fast clinical analyses. This approach could be used not only for drugs, but for any other endogenous or exogenous compounds.