Parallel, fluorous open-tubular chromatography using microstructured fibers.

Although commonly used in gas chromatography, open-tubular columns for liquid chromatography have seen their development hindered by a number of factors both theoretical and practical. Requiring small diameters, great lengths and specialized detection systems to achieve a proper chromatographic response, columns of this sort have largely been ignored despite the highly desirable column performance an optimized system would provide. Here, we introduce the use of microstructured fibers (MSFs) as a platform for the development of multiplexed open-tubular liquid chromatography (OTLC) columns. The multiple, parallel silica channels presented by the MSF act as a promising substrate for an OTLC column, as they have diameters near the ideal range for interactions (1-3 µm), minimize flow-induced backpressure through their many uniform paths, and increase the loading capacity compared to a single capillary channel of similar size. Additionally, with outer diameters comparable to regular fused silica capillaries, MSFs can easily be employed in conventional chromatographic systems, eliminating the need for specialized equipment. Finally, MSF columns of this type can be functionalized using silane coupling techniques to allow the introduction of a wide variety of stationary phase chemistries. While in this report we explore the potential and limitations of fluorine-functionalized MSFs as OTLC columns, other stationary phase materials could easily be substituted by choosing appropriate silanization reagents. Particular attention here will be paid to the physical and performance characteristics of the fabricated columns, as well as avenues for their improvement and implementation.

Fluorous monolith specificity: the effects of polymer density and secondary interactions on column performance and amenability to biological samples.

Continuing from the foundation laid by our previous work in the field, we present here an examination of the effects of monolith density and overall composition on the efficacy of performance in the realm of fluorous separations. By variation of the proportions of monomer and cross-linking agent relative to a static porogenic solvent composition, it was found that a composition of 30% polymer-forming material provides the optimal results in terms of resolution and peak shape for fluorous chromatography of a mixture of similarly labeled benzylamines. The presence of so-called "secondary interactions" that can compete with fluorous specificity in columns of this type were also examined and discussed, with similar results to those observed for commercial fluorous columns being noted. We suggest that these effects may actually be positive if they can be properly harnessed, as the ability to provide a second dimension for fluorous separations based on polarity may allow more complex analyses of labeled proteomic samples to be effectively undertaken. Finally, we present some initial results on the effectiveness of our optimized fluorous monoliths in a series of tagging and separation experiments using a custom-synthesized peptide. With successful resolution of labeled biological samples from their nonfluorous counterparts achieved, we discuss the potential expansion and further applicability of fluorous monoliths of this type in proteomic avenues, as well as their amenability to the greater analytical community.

Development of fluorinated, monolithic columns for improved chromatographic separations of fluorous-tagged analytes.

With applications that take advantage of highly selective fluorine-fluorine interactions appearing with greater frequency in the literature, the development of porous polymer monoliths from fluorous components is reported here for the purpose of chromatography of tagged analytes. With potential uses in fields as diverse as separation science and proteomics, facile fabrication of materials with fluorous specificity that can be applied in a high-throughput manner is greatly desirable. To this end, we have developed porous polymer capillary columns with varied fluorous content using a simple UV-initiated radical polymerization process and characterized them using flow-induced backpressure and scanning electron microscopy (SEM). With structural similarities assured (visually, and by backpressure variations of less than 42%), the monoliths were tested as chromatographic columns for the separation of a series of fluorous-tagged analytes under gradient conditions. It was found that columns made with fluorinated components exhibited greater selectivity for fluorous analytes than did equivalent, non-fluorinated monoliths, retaining analytes with either one or two fluorous tags for approximately 6% and 13% longer, respectively. This supports the idea of differences existing between fluorous and reverse-phase separation mechanisms, and encourages a broader range of potential applications for fluorous monoliths of this type.