Fast separation of enantiomers by capillary electrophoresis using a combination of two capillaries with different internal diameters

Characterization of linearly coupled capillaries with various inner diameters in the context of capillary electrophoresis

As a result of continuous instrumental progress, capillary electrophoresis has become an established separation technique. However, the choice of the suitable capillary inner diameter is sometimes difficult due to different instrumental requirements concerning injection, separation, or detection. To overcome this problem, we assembled two capillaries with different inner diameters, meaning that the inner diameter of the capillary at the injection side was different from that at the detection side. Since this was a rather uncommon approach, we focused on the associated effects in this proof-of-concept study. For the experiments, a non-aqueous model system was used, consisting of an acetonitrile-based background electrolyte and the two ferrocene derivates, ferrocenemethanol and decamethylferrocene. Using capillary flow injection analysis hyphenated to capacitively coupled contactless conductivity detection, it could be shown that fragmented capillaries of the same inner diameter had slightly lower volume flow rates than non-fragmented capillaries. With non-aqueous capillary electrophoresis hyphenated to UV detection, it was found that the coupling of capillaries with different inner diameter had a much stronger effect on the capillary electrophoresis flow than combinations with the same inner diameter. Additionally, if the inner diameter of the second capillary was larger than the inner diameter of the first capillary, a higher theoretical plate number and an increased sensitivity were found. Furthermore, it was found that there was no significant peak tailing introduced by the coupling.

Graphic abstract

Polyimide removal, cleaving, and fusion splicing of cylindrical and square fused silica capillaries for new separation and detection layouts in capillary electrophoresis and chromatography

Fusion splicing is an already mature technology used to join the ends of optical fibers in the telecommunication industry. However, there is a lack of reliable and well-described protocols to join the ends of fused silica microtubes or capillaries using fusion splicing. In this work, a step-by-step procedure is proposed and demonstrated to find the optimal operation conditions to splice the ends of fused silica capillaries by fusion. The two most appropriate and known technologies were tested and optimized: the microfurnace technique (or hot filament technique) and the electric arc technique. It is shown that both produce good splices when the capillaries are well cleaved. For this reason, the removal of the external coating, which is important for good cleavage, was also revised. The cleaving techniques were also compared among themselves. As a result, fusion splices of cylindric-to-cylindric, cylindric-to-square, and square-to-square capillaries are demonstrated. They have potential applications in new detection schemes and separation layouts in capillary electrophoresis, electrophoresis-based hydrodynamic concentrators, chromatography, cell sorters, and microfluidics in general.

Fast screening of aflatoxins in dairy cattle feeds with CE-LIF method combined with preconcentration technique of vortex assisted low density solvent-microextraction

Aflatoxin contamination in agricultural products poses a great threat to humans and livestock. The aim of this study was to establish a simple, rapid, highly sensitive, and inexpensive method for the simultaneous detection of aflatoxin B₁ , B₂ , G₁ , and G₂ in agricultural products. We used a vortex assisted low density solvent-microextraction (VALDS-ME) technique for sample preconcentration and sample detection was achieved with a CE-LIF method. Aflatoxins were separated in an uncoated fused-silica capillary with the MEKC mode and were excited by a 355 nm UV laser to produce native fluorescence for detection. The obtained LOD and LOQ for the four aflatoxins were in the range of 0.002-0.075 and 0.007-0.300 μg/L, respectively, and the analysis time was within 6.5 min. Using the established method, aflatoxins were screened in naturally contaminated dairy cattle feed samples including alfalfa, bran, and corn kernel. The result shows that the alfalfa and bran samples were contaminated with aflatoxins to varying degrees. Compared with other analytical techniques for aflatoxin screening in agricultural products, this CE-LIF method combined with VALDS-ME preconcentration technique is simple, rapid, highly efficient, and inexpensive.