2D separations on a 1D chip: gradient elution moving boundary electrophoresis-chiral capillary zone electrophoresis

Recent advances in microchip enantioseparation and analysis

This review summarizes recent developments (over the past decade) in the field of microfluidics-based solutions for enantiomeric separation and detection. The progress in various formats of microchip electrodriven separations, such as MCE, microchip electrochromatography, and multidimensional separation techniques, is discussed. Innovations covering chiral stationary phases, surface coatings, and modification strategies to improve resolution, as well as integration with detection systems, are reported. Finally, combinations with other microfluidic functional units are also presented and highlighted.

Separation and Detection of Trace Fentanyl from Complex Mixtures Using Gradient Elution Moving Boundary Electrophoresis

The current opioid epidemic remains an ongoing challenge, exacerbated by the extreme potency of synthetic opioids (e.g., fentanyl and fentanyl analogues), leading to an increase in adulterated heroin-related deaths. The increasing prevalence of fentanyl and fentanyl analogues in mixtures with heroin and other adulterants, excipients, and bulking agents has placed an emphasis on trace analysis methods for their detection from complex drug mixtures. Here, gradient elution moving boundary electrophoresis (GEMBE), a robust and miniaturized electrophoretic separation technique, was employed for the separation and detection of fentanyl and nine (9) fentanyl analogues from mixtures. GEMBE incorporated a short capillary (5 cm × 15 μm i.d.) for the electrophoretic separation of analytes with an opposing bulk counterflow. As the velocity of the counterflow was varied, analytes with differing electrophoretic mobilities entered the separation channel at different times and were analyzed as moving boundaries by contactless conductivity detection. The continuous injection of sample, driven by a controlled and variable pressure, both provided selectivity of the analytes and prevented contaminants or particulate within the sample from entering the separation capillary. Fentanyl was successfully separated and detected down to 2.5 μmol/L and demonstrated only 50% to 60% signal suppression in dilute binary mixtures with heroin and other common adulterants and excipients at 30:1 (compound/fentanyl) concentration ratios. In addition, GEMBE was successfully applied to a few adjudicated case samples of fentanyl-related mixtures exhibiting dyes and visible particulate. The short capillaries, contactless detection format utilized here, and continuous injection of sample allow for a small footprint platform that is easy-to-use for forensic analyses.

Using electrophoretic exclusion to manipulate small molecules and particles on a microdevice

Electrophoretic exclusion, a novel separations technique that differentiates species in bulk solution using the opposing forces of electrophoretic velocity and hydrodynamic flow, has been adapted to a microscale device. Proof-of-principle experiments indicate that the device was able to exclude small particles (1 μm polystyrene microspheres) and fluorescent dye molecules (rhodamine 123) from the entrance of a channel. Additionally, differentiation of the rhodamine 123 and polystyrene spheres was demonstrated. The current studies focus on the direct observation of the electrophoretic exclusion behavior on a microchip.

Recentchiral selectors for separation in HPLC and CE

Enantiomers (stereoisomers) can exhibit substantially different properties if present in chiral environments. Since chirality is a basic property of nature, the different behaviors of the individual enantiomers must be carefully studied and properly treated. Therefore, enantioselective separations are a very important part of separation science. To achieve the separation of enantiomers, an enantioselective environment must be created by the addition of a chiral selector to the separation system. Many chiral selectors have been designed and used in various fields, such as the analyses of drugs, food constituents and agrochemicals. The most popular have become the chiral selectors and/or chiral stationary phases that are of general use, i.e., are applicable in various separation systems and allow for chiral separation of structurally different compounds. This review covers the most important chiral selectors / chiral stationary phases described and applied in high performance liquid chromatography and capillary electrophoresis during the period of the last three years (2008–2011).