ELECTROPHORESIS最新文献

This work focuses on the separation of oligonucleotides (ONs) in a free solution by capillary electrophoresis—mass spectrometry (CE-MS). Specifically, we evaluated a combination of separation in acidic background electrolytes (BGEs), nanospray ionization, and time-of-flight mass spectrometry in positive mode. A mixture of synthetic ONs, ranging in length from 15 to 78 nt, was employed as the test compounds. The key to a good separation selectivity of ONs lies in the different protonation of individual nucleobases. To this end, we assessed the acidity constant (pK_a) of the nucleobases in nucleotides experimentally as 3.3 for adenine, 4.4 for cytosine, 2.5 for guanine, and < 2 for thymine. From a set of separations in the 2–9 pH range, it was found that optimum peak shape and resolution are achieved in the interval of acidic pH 2–2.5. The BGE can be conveniently composed of either formic acid (FA) or a combination of ammonium hydroxide and FA. Nanospray ionization provided ions with charge numbers ranging from +4 to +8, proportional to the length of the ON. For short sequences, sheath liquid (SL) comprising 0.5%–1% (v/v) FA + 20% (v/v) methanol was sufficient in order to generate ions in positive mode MS, whereas a stronger SL of 5% (v/v) FA + 20% (v/v) methanol was required for longer ON sequences of approximately > 40 nt.

Substandard and falsified medicines pose a significant public health threat, particularly in low-income countries. Ensuring pharmaceutical quality is crucial to mitigate risks associated with ineffective and harmful medications. Among others, developing and implementing robust and cost-effective analytical methods is an important and quick strategy for ensuring the quality of medicines. This study aimed to develop a robust and cost-effective capillary zone electrophoresis method with UV detection for insulin analysis in active pharmaceutical ingredient and formulations. A multilayer capillary coated with polybrene and poly(sodium 4-styrenesulfonate) improved repeatability. The method was optimized by systematically evaluating running buffer composition, pH, ionic strength, and voltage, achieving optimal separation with a 60 mM phosphate buffer at pH 8.0. It demonstrated excellent precision, accuracy, linearity, and robustness. Application of the method to insulin commercial samples verified compliance with pharmacopoeial standards. The method could be a reliable and accessible alternative for quality control of insulin in resource-limited settings, supporting efforts to combat substandard pharmaceuticals and protect public health. Moreover, the method aligns with green chemistry principles, as it eliminates the need for organic solvents, either as solvent or as a component of the running buffer.

A novel microdroplet mixer is proposed by combining the asymmetric offset structure with tunable shrink in the microfluidic chip. The mixer consists of a coaxial flow region in the dispersed-phase channel and an asymmetrical offset aggregation region in the downstream channel, which shortens the mass transfer distance between the solutions to be mixed through the “sandwich” type of initial distribution, and utilizes the tunable shrink to reduce the shear force and break the symmetric vortex during the generation of the microdroplets, prolonging the pre-mixing time. Through finite element simulation, the effects of dispersed-phase flow velocity, continuous-phase flow velocity, the relative angles and offset distances between the continuous and dispersed-phases, and the necking width and length of the tunable shrink on the mixing efficiency inside the droplets were investigated. The internal mixing inside the microdroplet decrease with the dispersed-phase flow velocity, whereas the increase of the continuous-phase flow velocity favors the mixing enhancement. By optimizing the above-mentioned effects, the mixing efficiency achieves as high as approximately 97%, demonstrating the excellent mixing inside the microdroplets in the novel asymmetric micromixer. The proposed microdroplet mixer illustrates advantages of rapid mixing, simple patterned geometry, and easy to fabricate, demonstrating a promising technique for flexibly fluid mixing inside the microdroplet on a microfluidic chip.

Nonlinear electrophoresis (EP) has seen significant advancements over the past five decades, evolving into a potent electrokinetic phenomenon with transformative potential for analytical chemistry, particularly in the areas of bioanalysis and separations. This review chronicles the historical development of nonlinear EP, from its foundational Russian-language publications in the 1970s to its current applications enabling highly discriminatory separations of particles ranging from nanoparticles to large cells, exploiting subtle analyte differences. This review article is organized in three distinct eras: the 1970s, from 1980 to 2000, and from 2000 to the present. The latter is covered in terms of the advances in theory and modeling and the advances in experimental applications. The established regimes of classical nonlinear EP, currently utilized for electrophoretic separation of viruses, cells, and various micro- and nanoparticles, are discussed. Despite these breakthroughs, significant research opportunities remain, including the development of analytical expressions for dielectric particles at intermediate Peclet numbers (1 < Pe < 10), the application of AC signals for purely nonlinear separations, and understanding the migration of highly charged particles with thick electrical double layers. This article aims to provide experimentalists with a clear and accessible overview of the history and key advancements of nonlinear EP, highlighting its flexibility and positioning it as a major future player in bioanalytical chemistry.

The separation of live and dead cells is crucial for the diagnosis of early-stage diseases and efficacy test of drug screening, etc. We demonstrate the biological application of our recently developed AC insulator-based dielectrophoresis (AC iDEP) technique for the separation of live and dead yeast cells in a virtually infinitely long ratchet microchannel. This separation arises from the variation of surface charge and in turn electrokinetic velocity when yeast cells lose viability, as compared to the varying dielectrophoretic responses in conventional dielectrophoretic methods. The live and dead yeast cells can be focused toward the channel centerline and ratchet base, respectively, under AC voltages within a selected frequency and amplitude window. The performance of this cell viability-based AC iDEP separation is evaluated using the separation efficiency, which is reasonably predicted by a numerical model.