Pablo A. Kler

Zero-dead-volume interfaces for two-dimensional electrophoretic separations: Microfluidics and Miniaturization

We present the study on the sample transfer characteristics of two different microfluidic interfaces for 2D‐CE . These interfaces were manufactured using two different microfabrication technologies: one was obtained via the classical photolithography—wet etching—anodic‐bonding process; and the other was obtained via the selective laser‐induced etching process. The comparison of the two interfaces, and an intact capillary as a reference, was made via the CE separation of amino acids (arginine and lysine) under different bulk flow conditions, with and without applying bias potential to the secondary channels. The influence on peak shapes, migration times, and repeatabiliy were evaluated.

Short Communication:Zero‐dead‐volume interfaces for two–dimensional electrophoretic separations

We present the study on the sample transfer characteristics of two different microfluidic interfaces for 2D‐CE . These interfaces were manufactured using two different microfabrication technologies: one was obtained via the classical photolithography—wet etching—anodic‐bonding process; and the other was obtained via the selective laser‐induced etching process. The comparison of the two interfaces, and an intact capillary as a reference, was made via the CE separation of amino acids (arginine and lysine) under different bulk flow conditions, with and without applying bias potential to the secondary channels. The influence on peak shapes, migration times, and repeatabiliy were evaluated.

Design keys for paper-based concentration gradient generators

The generation of concentration gradients is an essential operation for several analytical processes implemented on microfluidic paper-based analytical devices. The dynamic gradient formation is based on the transverse dispersion of chemical species across co-flowing streams. In paper channels, this transverse flux of molecules is dominated by mechanical dispersion, which is substantially different than molecular diffusion, which is the mechanism acting in conventional microchannels. Therefore, the design of gradient generators on paper requires strategies different from those used in traditional microfluidics. This work considers the foundations of transverse dispersion in porous substrates to investigate the optimal design of microfluidic paper-based concentration gradient generators (μPGGs) by computer simulations. A set of novel and versatile μPGGs were designed in the format of numerical prototypes, and virtual experiments were run to explore the ranges of operation and the overall performance of such devices. Then physical prototypes were fabricated and experimentally tested in our lab. Finally, some basic rules for the design of optimized μPGGs are proposed. Apart from improving the efficiency of mixers, diluters and μPGGs, the results of this investigation are relevant to attain highly controlled concentration fields on paper-based devices.

Fundamental aspects of electromigrative separation techniques

Electromigrative separation techniques currently present an excellent option for the analysis of important analytes for various industrial and scientific application fields. A large number of different separation modes exist, which are based on different physicochemical properties (i.e., different separation mechanisms) of the analytes and working buffers. These allow development of efficient and specific methods for the targeted applications mostly using the same equipment. Tailoring selectivity is possible with the addition of secondary selectors acting by complexation, ion-pairing, or affinity binding among others. Sensitivity and selectivity can be addressed using various detection systems, including, most often optical, conductivity and mass spectrometric detection. A clear benefit of electromigrative separation techniques is their comparatively low operation and maintenance costs, due to the low consumption of solvents and other disposable materials, but also due to the robustness of the equipment, with few mobile parts. All these advantages have driven electromigrative separations to be among the most popular analytical techniques for portable and miniaturized devices for targeted and in-place analysis. In addition, the high ratio between analytical performance versus operational cost coerced the industry to develop high throughput and automated equipment for high numbers of samples, both in classic and miniaturized formats. Finally, there is a last but major benefit of electromigrative separation techniques: in contrast to chromatographic techniques, a well validated collection of mathematical models exists that describes comprehensively all physicochemical processes taking place during electromigration. All these models are not only able to explain the analyte migration behavior and the performance of different separation mechanisms but they also enable the scientific community to understand and predict separation effects, mechanisms, and phenomena. It is especially the combination of well-chosen experimental designs and theoretical considerations that make electromigrative separation a prospering field of research, enabling novel applications in various fields such as pharmaceutical, biotechnological, and food science. In this topical collection, we thus focus on these fundamentals of electromigrative separation techniques on the one hand. Examples in this special issue are, e.g., unusual stacking phenomena, theory of affinity electrophoresis, and quantitative aspects of isotachophoresis. On the other hand, evolution of the techniques has to be supported and further developed by instrumental innovations. Two major topics are evolving recently: coupling electromigrative separation technique with mass spectrometric detection, and two-dimensional separations. The first enabled reaching high sensitivity Published in the topical collection Fundamental Aspects of Electromigrative Separation Techniques with guest editors Carolin Huhn and Pablo A. Kler.